Basic concepts of size deviations and tolerances. Basic concepts of dimensions, limit deviations and tolerances. Where deviations apply and how they are indicated

METHODOLOGICAL INSTRUCTIONS

performing laboratory and control work on the discipline

"Fundamentals of metrology, standardization and certification"

for students of the specialty 31.14.00 - "Electrification and Automation of Agriculture", 26.02.00 - "Woodworking Technology", 31.10.00 - "Land Cadastre".

Tyumen 2010

Compiled by: Nemkov M.V. – Cand. tech. Sciences, Associate Professor

Golovkin A.V. – Cand. teacher Sciences, Associate Professor

Christel M.A. - assistant

Golovkina E.A. - Applicant

Reviewer: Belov A.G. - Cand. tech. Sciences, Associate Professor

Guidelines for the performance of laboratory and control work in the discipline "Fundamentals of Metrology, Standardization and Certification" are made in accordance with the State Educational Standard in the field of "Agroengineering".

A method for calculating typical connections and assigning limit deviations and fits in mechanical engineering is presented, taking into account the Unified System of Tolerances and Fits. The methodological instruction contains the initial data for performing laboratory and control work on variants and normative standard material.

The methodical instruction is intended for students of specialties 31.14.00 - "Electrification and automation of agriculture", 26.02.00 - "Woodworking technology", 31.10.00 - "Land cadastre".

INTRODUCTION

With the modern development of science and technology, the organization of production, standardization, based on the widespread introduction of the principles of interchangeability, is one of the most effective means of promoting progress in all areas of economic activity and improving the quality of products.

One of the main tasks of a mechanical engineer is the creation of new and modernization of existing products, the preparation of drawing documentation that helps to ensure the necessary manufacturability and high quality of products. The solution of this problem is directly related to the choice of the required accuracy of manufacturing products, the calculation of dimensional chains, the choice of tolerances for deviations from the geometric shape and location of surfaces.

PURPOSE OF THE WORK

To consolidate the theoretical provisions of the course "Fundamentals of Metrology, Standardization and Certification", to instill skills in using reference material, to acquaint students with the main types of tolerance and landing calculations.

3.1.1. For a smooth cylindrical connection of nominal diameter D, determine:

limit dimensions,

Tolerances

The largest, smallest and average gaps,

landing permit,

Executive dimensions of limit gauges.

3.1.2. The location of the tolerance fields is shown graphically.

3.1.3. The student makes calculations, draws tolerance fields, draws up a report based on the results of the calculation and practical work.

3.2.1. To study the methodology for calculating dimensional chains, which ensures complete interchangeability.

3.2.2. Determine the nominal value, limit deviations and tolerance of the master link.

3.2.3. Draw a diagram of a dimensional chain graphically.

3.3.1. To study the method of calculating the tolerances and landings of bearings.

3.3.2. Select the fit of the inner and outer rings of the rolling bearing.

3.3.3. Show graphically the location of the tolerance fields.

3.4.1. To study the methodology for determining tolerances and fits of threaded connections.

3.4.2. Determine the limiting dimensions of metric thread elements.

3.4.3. Draw a diagram of the location of the tolerance fields.

3.5.1. To study the method of calculating tolerances and landings of splined joints.

3.5.2. Determine the tolerances and limit dimensions of the elements of the spline connection.

3.5.3. Draw a diagram of the location of the tolerance fields.

3.5.4. Provide an assembly drawing of the spline connection.

3.6.1. To study the method of calculating the tolerances and landings of keyed connections.

3.6.2. Determine the tolerances and limit dimensions of the keyed connection elements.

3.6.3. Draw a diagram of the location of the tolerance fields.

3.6.4. Provide an assembly drawing of the keyed connection.

material support

4.1. Methodical instructions.

4.2. Exercise ( applications 1 - 7).

4.3. Reference material ( Myagkov V.D. Tolerances and landings. Directory. Leningrad: Mashinostroenie, 1982.).

Work organization

Laboratory and control work consists of six tasks in the main sections of the course "Fundamentals of Metrology, Standardization and Certification". Tasks are composed in thirty versions. The number of each student's option is determined by the teacher during the orientation lecture.

In addition to formulating tasks and presenting options for tasks, the guidelines also include the necessary theoretical material, the methodology for determining tolerances and fits of the types of joints under consideration, examples of tasks, part of the reference material ( applications). As a literary source necessary for solving all types of problems, the Handbook edited by V.D. Myagkov "Tolerances and Landings", Leningrad: Mashinostroenie, 1982 (2 volumes) is proposed.

A report on the results of laboratory and control work is drawn up and submitted to the teacher before the start of the examination session.

Task number 1

Measuring instruments

measuring instrument- technical device intended for measurements, having metrological characteristics. By design they are divided into:

- Measure - is a measuring instrument designed to reproduce
(single-digit - weight, multi-digit - scale bar, standard
samples, a set of measures - a set of weights, etc.)

- Measuring device - is a measuring instrument for
generating a signal of information available for perception
observer.

- Measuring setup - is a set of functional
combined measuring instruments designed to develop
signal information in the form of information that is easy to understand.

- Measuring system - is a set of measuring instruments,
interconnected by communication channels, intended for
generating a signal of information in a form convenient for automatic
processing.

Indicators of measuring instruments (passport data):

- Scale division price - the difference in the values of the quantities corresponding to
two adjacent scale marks (for example, 1mm - for a measuring ruler,
0.1mm - for calipers, etc.);

- Indication range - range of the scale, limited by its
start and end readings (e.g. 0-1 mm for
micrometer - full one turn of the arrow);

- Limit of measurements - largest or smallest range value
measurements (for example, up to 10 mm - for a micrometer);

- Accuracy of measuring instruments - quality of measuring instruments,
characterizing the proximity to zero of their errors (for a measuring ruler
1mm, for calipers - 0.1mm).

The types of measurements are classified according to the following types:

In terms of accuracy:

- Equivalent(a series of measurements performed with the same accuracy
SI and under the same conditions;

- unequal(a series of measurements performed by several measuring instruments with different accuracy and under different conditions);

By the number of measurements:

- Single(measurement taken once);
Multiple(measurement consisting of a series of single measurements)

In relation to the change in the measured value:

- Static(measurement of time-invariant physical

values);

- dynamic(measurement of a physical quantity changing in size); According to the expression of the measurement result:

- Absolute(measurements based on direct measurements
quantities);

- relative(measurement of the ratio of magnitude to a single
value acting as a unit)

According to the methods of obtaining measurement results:

- Direct(measurement, the value of a physical quantity is obtained

directly);

- Indirect(measurement at which the value of the physical
quantities are determined on the basis of direct measurements of other
physical quantities);

Measurement methods are classified according to the following criteria:

According to the general methods of obtaining measurement results;

- direct method measurements (direct measurement);

- Indirect measurement method (measurement through other quantities);
According to the measurement conditions:

- Contact measurement method (device element in contact with the object of measurement, for example, a thermometer);

- Contactless measurement method - the device element is not in contact with the object, for example, a locator

According to the method of comparing the measured value:

- Direct evaluation method- the value of the quantity
determined directly by SI, for example, a thermometer

- Measure comparison method - measured value is compared

with a reproducible measure, e.g. weight measurement on a balance scale.

Measurement error:

Absolute error - the difference between the measurement result and the true (actual) value of the measured value, (for example, 0.5 mm - for a measuring ruler with a scale division of 1 mm, for devices it is indicated in the passport);

Relative error- this is the absolute error, expressed in fractions of the measured value in%. For example, the measured length of an object is 50mm, with an error of 0.5mm, the relative error will be (0.5: 50) x 100% = 1%

Length measurement:

Measuring instrument - measuring ruler 1m. Measuring metal rulers are made of steel spring heat-treated tape with a light-polished surface up to 1 m long with a division value of 1 mm.

1. Measure the length and width of the table.

2. Measure the length and width of the notebook (book).

What is it measuring instrument

Type of measurements;

Measurement method;

Temperature measurement:

The measuring instrument is a thermometer.

1. Measure the air temperature in the room.

2. Measure the outside air temperature.

Determine (name) using the application:

What is it measuring instrument by design;

Indicators of measuring instruments;

Type of measurements;

Measurement method;
- relative and absolute errors;

Mass measurement:

Measuring instrument - cup dial scales.

1. Measure the mass of one book.

2. Measure the mass of three books

Determine (name) using the application:

What is it measuring instrument by design;

Indicators of measuring instruments;

Type of measurements;

Measurement method;

Relative and absolute errors;

Sample Diameter Measurement:

The measuring instrument is a caliper.

1. Measure the diameter of the handle.

2. Measure the diameter of the pencil.

Define (name), (using table 1):

What is it measuring instrument by design;

Indicators of measuring instruments;

Type of measurements;

Measurement method;

Relative and absolute errors;

Table 1 - Technical characteristics of tools

Tool	Type, model	Manufacturer	Nonius report, mm	Measurement range, mm	Permissible error, mm
Calipers	ShTs-1	Caliber	0,1	0-125	±0.06
ShTs-2	LIPO	0,05; 0,1	0-150	±0.06
CHIZ	0-250	±0.08
ShTs-3	LIPO	0,1	0-160	±0.06
CHIZ	0-400	±0.09
stiz	250-630	±0.09
stungenreismus	SHR-250	KRIN	0,05	0-250	±0.05
SHR-400	0,05	40-400	±0.05
ShR-630	0,1	60-630	±0.10
Depth gauge	SHG-160	KRIN	0,05	0-160	±0.05
SHG-250	0-250
SHG-400	0-400

Measurement of blood pressure, pulse rate and respiration:

Measuring instrument - tonometer, stopwatch.

1. Measure the pulse.

2. Measure the respiratory rate.

Determine (name) using the application:

What is it measuring instrument by design;

Indicators of measuring instruments;

Type of measurements;

Measurement method;

Relative and absolute errors;

Sample Thickness Measurement:

The measuring instrument is a micrometer.

1. Measure the thickness of a sheet of paper.

2. Measure the thickness of the book cover.

Define (name), (using table 2):

What is it measuring instrument by design;

Indicators of measuring instruments;

Type of measurements;

Measurement method;

Relative and absolute errors;

Table 2 - Technical characteristics of micrometric instruments

Tool	Type, model	Manufacturer	Graduation mm	Measurement range, mm	Permissible error, mm
Micrometer smooth	MK-25	Caliber	0,01	0-25	±0.004
MK-50	25-50
MK-75	50-75
MK-100	75-100
MK-125	KRIN	0,01	100-125	±0.005
MK-150	125-150
MK-175	150-175
MK-200	175-200
Micrometric depth gauge	GM-100	KRIN	0,01	0-100	±0.005
GM-150	0-150
Inside micrometer	HM50-75	CHIZ	0,01	50-75	±0.004
HM75-100	75-175	±0.006
HM75-600	75-600	±0.015

Length and width measurement:

The measuring instrument is a tape measure. Measuring metal tapes are made of invar, stainless steel and bright polished steel tape with lengths of 1, 2, 5, 10, 20, 30, 40, 50, 75, 100 m. They are produced in the 2nd and 3rd accuracy classes. Permissible deviations | The actual length of the millimeter divisions of the tape measures should be no more than ± 0.15 and ± 0.20 mm, centimeter - no more than ± 0.20 and ± 0.30 mm, decimeter and meter - no more than ±0.30 and ±0.40 mm for the 2nd and 3rd accuracy classes, respectively.

1. Measure the length of the chalkboard.

2. Measure the width of the chalkboard.

3. Determine the area of the board

Determine (name) using the application:

What is it measuring instrument by design;

Indicators of measuring instruments;

Type of measurements;

Measurement method;

Relative and absolute errors;

Task number 2

"Tolerances and fits of smooth cylindrical joints"

Limit sizes.

Tolerances.

landing permit.

Tolerance and landing system

Tolerance and landing system they call a set of series of tolerances and landings, naturally built on the basis of experience, theoretical and experimental studies and designed in the form of standards. The system is designed to select the minimum necessary, but sufficient for practice, options for tolerances and fittings of typical connections of machine parts, makes it possible to standardize cutting tools and gauges, facilitates the design, production and achievement of interchangeability of products and their parts, and also determines the achievement of their quality.

The ISO system of tolerances and fits for typical machine parts is built according to uniform principles. Landings are provided in the hole system ( SA) and in the shaft system ( SW) (fig.4 ). Landings in the hole system- landings in which various gaps and interferences are obtained by connecting various shafts with the main hole ( Fig.4, a ), which is denoted H. Fits in the shaft system- landings in which various gaps and interferences are obtained by connecting various holes to the main shaft ( Fig.4, b ), which stands for h.

Figure 4 - Examples of the location of tolerance fields for landings

in the hole system (a) and in the shaft system (b)

For all fits in the hole system, the lower deviation of the hole EI=0, i.e. the lower limit of the tolerance field of the main hole, always coincides with the zero line. For all fits in the shaft system, the upper deviation of the main shaft es=0, i.e. the upper limit of the shaft tolerance field always coincides with the zero line. The tolerance field of the main hole is laid up, the tolerance field of the main shaft is down from the zero line, i.e. to the part material.

Such a system of tolerances is called one-sided limit.

In the hole system, there are fewer holes of various sizes than in the shaft system, and therefore, the range of cutting tools required for hole processing is smaller. Concerning the hole system has become predominant.

For the formation of fits with different gaps and interferences in the ISO system for sizes up to 500 mm, 27 options for the main deviations of shafts and holes are provided. Basic deviation- this is one of two deviations (upper or lower) used to determine the position of the tolerance field relative to the zero line ( fig.5 ).

Each letter indicates a number of basic deviations, the value of which depends on the nominal size.

The main deviations of the holes are designed to provide fits in the shaft system similar to fits in the hole system. They are equal in absolute value and opposite in sign to the main deviations of the shafts denoted by the same letter.

Figure 5 - Main deviations accepted in the ISO system

In each product, parts of different values are produced with different accuracy. To normalize the required levels of accuracy, the qualifications for the manufacture of parts and products are established. Under quality understand a set of tolerances characterized by constant relative accuracy for all nominal sizes of a given range (for example, from 1 to 500 mm). Accuracy within one quality depends only on the nominal size.

The ISO system has 19 qualifications: 01,0,1,2, ..., 17. For grades 5-17, when moving from one grade to the next, coarser one, the tolerances increase by 60%. Every five qualifications, tolerances increase 10 times.

For each qualification built tolerance series, in each of which different sizes have the same relative accuracy.

To build tolerance series, each of the size ranges, in turn, is divided into several intervals. For nominal sizes from 1 to 500 mm, 13 intervals are established: up to 3, over 3 to 6, over 6 to 10 mm, ..., over 400 to 500 mm. For all sizes combined into one interval, for example, for sizes over 6 to 10 mm, the tolerance values \u200b\u200bare taken the same.

Caliber

The suitability of parts with a tolerance of IT6 to IT17, especially in mass and large-scale production, is most often checked by limit gauges. A set of working limit gauges for controlling the dimensions of smooth cylindrical parts consists of a through gauge ETC(it controls the size limit corresponding to the maximum material of the object being checked, fig.6 ) and non-going caliber NOT(they control the limit size corresponding to the minimum material of the object being checked). With the help of limit gauges, it is not the numerical value of the controlled parameters that is determined, but the suitability of the part, i.e. find out whether the controlled parameter goes beyond the lower or upper limit, or is between two available limits.

Figure 6 - Scheme for choosing nominal sizes

limiting smooth calibers

The part is considered fit if the passing gauge (going side of the gauge) passes under the action of its own weight or a force approximately equal to it, and the non-going gauge (non-going side) does not pass through the controlled surface of the part. In this case, the actual size of the part is between the given limit sizes. If the pass gauge fails, the part is a repairable defect; if the non-going gauge passes, the part is an irreparable defect, since the size of such a shaft is less than the smallest allowable limit size of the part, and the size of such an opening is greater than the largest allowable limit size.

To control gauges-brackets are used control gauges K-I, which are impassable and serve for withdrawal from operation due to wear of the through-hole working brackets.

Clamps are mainly used to control the shafts. The most common one-sided double-limit brackets ( fig.7 ).

Figure 7 - One-sided double-limit brackets

Caliber tolerances

GOST 24853-81 for smooth gauges establishes the following manufacturing tolerances: H- working gauges (plugs) for holes ( Hs- the same calibers, but with spherical measuring surfaces); H 1- gauges (brackets) for shafts; H p- control gauges for staples ( fig.8 ).

For passing gauges that wear out during the control process, in addition to the manufacturing tolerance, a wear tolerance is provided. For sizes up to 500 mm gauge wear ETC with a tolerance of up to IT8 inclusive, it can go beyond the tolerance field of the part by an amount Y for traffic jams and Y 1 for staples; for calibers ETC with tolerances from IT9 to IT17, wear is limited by the passage limit, i.e. Y= 0 and Y 1 = 0.

For all pass gauges tolerance fields H(Hs) and H 1 shifted inside the tolerance field of the product by an amount Z for plug gauges and Z1 for clip gauges.

The values Z, Y, Z 1 , Y 1 , H, H s , H 1 , H p required to perform the calculation and practical work are given in application 2.

Figure 8 - Diagrams of the location of tolerance fields for calibers:

a - for the hole;

b - for the shaft

An example of the calculation work

For a smooth cylindrical connection H7/h6 with a nominal diameter D = 24 mm, we determine:

1. Limit sizes.

2. Tolerances.

3. Largest, smallest and average gaps.

4. landing permit.

5. Executive dimensions of limit gauges.

The location of the tolerance fields is shown graphically.

1. We determine the limiting dimensions.

Landing 24 H7/h6 is a clearance fit in the hole system. Tolerance field of the main hole H7 for diameter 24 mm determined by table 1.27 [1 ]:

ES = +0.021 mm;

Shaft tolerance field (6th grade) for diameter 24 mm determined by table 1.28 [1 ]:

es = 0;

ei = -0.013 mm.

Let's determine the limiting dimensions of the hole:

D max = D + ES = 24.000 + 0.021 = 24.021(mm);

D min \u003d D + EI \u003d 24.000 + 0 \u003d 24.000 (mm).

Let's determine the limiting dimensions of the shaft:

d max = d + es = 24.000 +0 = 24.000 (mm);

d min \u003d d + ei \u003d 24.000 + (-0.013) \u003d 23.987 (mm).

2. Determine the tolerances.

Determine the hole diameter tolerance:

TD = D max - D min = 24.021 - 24.000 = 0.021 (mm);

Td = d max - d min = 24.000 - 23.987 = 0.013 (mm).

3. Determine the largest, smallest and average gaps.

Maximum gap:

S max \u003d D max - d min \u003d 24.021 - 23.987 \u003d 0.034 (mm).

Smallest clearance:

S min \u003d D min - d max \u003d 24.000 - 24.000 \u003d 0 (mm).

Average clearance:

S m \u003d (S max + S min) / 2 \u003d (0.034 + 0) / 2 \u003d 0.017 (mm).

4. Determination of fit tolerance.

We determine the tolerance in landing with a gap:

TS \u003d S max - S min \u003d 0.034 - 0 \u003d 0.034 (mm).

5. We determine the executive dimensions of the limit gauges.

5.1. We determine the dimensions of the calibers-plugs.

For hole diameter 24 mm with tolerance field H7(7th grade) is determined according to GOST 24853 -81:

H = 4 µm = 0.004 mm;

Z = 3 µm = 0.003 mm;

Y = 3 µm = 0.003 mm.

The largest size of the through passage new caliber-cork:

PR max \u003d D min + Z + H / 2 \u003d 24.000 + 0.003 + 0.004 / 2 \u003d 24.005 (mm).

The smallest size of the through passage of a new plug gauge:

PR min \u003d D min + Z - H / 2 \u003d 24.000 + 0.003 - 0.004 / 2 \u003d 24.001 (mm).

The smallest size of a worn plug gauge:

PR out \u003d D min - Y \u003d 24.000 - 0.003 \u003d 23.997 (mm).

The largest size of the non-going new plug gauge:

NOT max \u003d D max + H / 2 \u003d 24.021 + 0.004 / 2 \u003d 24.023 (mm).

The smallest size of a non-going new plug gauge:

NOT min \u003d D max - H / 2 \u003d 24.021 - 0.004 / 2 \u003d 24.019 (mm).

5.2. We determine the dimensions of the gauges-brackets.

For shaft diameter d = 24 mm with tolerance field h6(6th grade) is determined according to GOST 24853 -81:

H 1 \u003d 4 μm \u003d 0.004 mm;

Z 1 \u003d 3 μm \u003d 0.003 mm;

Y 1 \u003d 3 μm \u003d 0.003 mm.

H p \u003d 1.5 μm \u003d 0.0015 mm.

The largest size of the through passage of the new caliber-brackets:

PR max \u003d d max - Z 1 + H 1 / 2 \u003d 24.000 - 0.003 + 0.004 / 2 \u003d 23.999 (mm).

The smallest size of the through passage of the new caliber-bracket:

PR min \u003d d max - Z 1 - H 1 / 2 \u003d 24.000 - 0.003 - 0.004 / 2 \u003d 23.995 (mm).

The largest size of the worn-through caliber-bracket:

PR out \u003d d max + Y 1 \u003d 24.000 + 0.003 \u003d 24.003 (mm).

The largest size of the non-going new caliber-bracket:

NOT max \u003d d min + H 1 / 2 \u003d 23.987 + 0.004 / 2 \u003d 23.989 (mm).

The smallest size of the non-going new caliber-bracket:

NOT min \u003d d min - H 1 / 2 \u003d 23.987 - 0.004 / 2 \u003d 23.985 (mm).

Dimensions of control gauges:

K-PR max \u003d d max - Z 1 + Hp / 2 \u003d 24.000 - 0.003 + 0.0015 / 2 \u003d 23.99775 (mm).

K-PR min \u003d d max - Z 1 - Hp / 2 \u003d 24.000 - 0.003 - 0.0015 / 2 \u003d 23.99625 (mm).

K-NOT max \u003d d min + Hp / 2 \u003d 23.987 + 0.0015 / 2 \u003d 23.98775 (mm).

K-NOT min \u003d d min - Hp / 2 \u003d 23.987 - 0.0015 / 2 \u003d 23.98625 (mm).

K-I max \u003d d max + Y 1 + Hp / 2 \u003d 24.000 + 0.003 + 0.0015 / 2 \u003d 24.00375 (mm).

K-I min \u003d d max + Y 1 - Hp / 2 \u003d 24.000 + 0.003 - 0.0015 / 2 \u003d 24.00225 (mm).

6. The location of the tolerance fields is shown on rice. 9.

Figure 9 - Location of tolerance fields

Attachment 1

Task options

for work

Option	Nominal dimensions, mm	Connection types	Option	Nominal dimensions, mm	Connection types
		H7/k6			H7/h6
		H7/i7			G6/h7
		G6/h6			H6/h7
		K8/h7			H6/g6
		H6/i s 6			G6/h7
		K7/h8			H6/f6
		H7/k7			F8/h7
		H6/i s 6			H7/g6
		H7/h7			J s 6/h6
		K6/h6			K6/h7
		E8/h7			M6/h7
		H6/f6			H6/k6
		G7/h8			M6/h7
		H7/d7			H6/i s 6
		H6/f6			M8/h7

Annex 2

Gauge tolerances and deviations

(according to GOST 24853-81)

Qua-	Designation	Size intervals, mm
whether-	sizes and	St. 18 to 30	St.30 to 50	St.50 to 80	Over 80 to 120	Over 120 to 180
theta	tolerances	dimensions and tolerances, microns
	Z		2,5	2,5
	Y	1,5
	Z1		3,5
	Y 1
	H, Hs	2,5	2,5
	H1
	Hp	1,5	1,5		2,5	3,5
	Z, Z1		3,5
	Y, Y 1
	H, H1
	Hs	2.5	2,5
	Hp	1,5	1,5		2,5	3,5
	Z, Z1
	Y, Y 1
	H
	H1
	H s , H p	2,5	2,5

Task number 3

"Tolerances and fittings of rolling bearings"

Accuracy class.

bearing number.

An example of the calculation work

For a radial single-row bearing, construct tolerance fields with deviations. Loading - circulating. The shaft is solid.

Initial data:

1. Accuracy class - 0.

2. Bearing number - 224.

4. The nature of the loading - with moderate shock and vibration.

1. According to GOST 8338 - 75 for bearing No. 224 are determined:

d = 120 mm - diameter of the inner ring;

D = 215 mm - diameter of the outer ring;

B = 40 mm - bearing width;

r = 3.5 mm is the coordinate of the mounting chamfer of the bearing ring.

2. Determine the intensity of the load on the seating surface of the solid shaft neck:

P r = R × Kn × F × Fa / b = 6000 × 1 × 1 × 1 / 0.033 = 181818 (N/m) » 182 (kN/m),

where = 1.0 for a load with moderate shocks and vibrations; F=1 with a solid shaft; Fa = 1 for radial bearings; b=B-2r\u003d 40 - 2 × 3.5 \u003d 33 (mm) \u003d 0.033 (m).

3. The found value of the load intensity P r \u003d 182 kN / m corresponds to the shaft tolerance fields j s 5 and j s 6. With an accuracy class of 0, the recommended tolerance fields are n6; m6; k6; js6; h6; g6. The shaft tolerance field chosen in this way is j s 6.

By tab. 1.29 [1 ] for d = 120 mm tolerance field j s 6 correspond to:

es = + 0.011 mm;

ei = – 0.011 mm.

Deviations of the diameter of the inner ring of the bearing d = 120 mm for accuracy class 0 are accepted according to GOST 520 - 89:

upper deviation - 0;

lower deviation - 0.020 mm.

4. For accuracy class 6, one of the recommended housing hole tolerance fields is selected. The preferred tolerance field is H7.

By tab. 1.27 [1 ] for D = 215 mm tolerance field H7 correspond to:

ES=+0.046mm;

The deviation of the diameter of the outer ring of the bearing D = 215 mm for accuracy class 0 are accepted according to GOST 520 - 89:

upper deviation - 0;

lower deviation - 0.030 mm.

4. The layout of the tolerance fields is shown on pic 11 .

Figure 11 - Schemes for the location of tolerance fields

a) for connecting the shaft with the inner ring of the bearing;

b) to connect the outer ring of the bearing with the housing.

Annex 3

Task options

for work

Option	No. bearing bearing	Accuracy class	R, H	Characteristics of loading	Option	No. bearing bearing	Accuracy class	R, H	Characteristics of loading
				FROM					At
				FROM					FROM
				At					FROM
				At					At
				FROM					At
				FROM					FROM
				At					FROM
				At					At
				FROM					At
				FROM					FROM
				At					FROM
				At					At
				FROM					At
				FROM					FROM
				At					FROM

Appendix 4

Bearing dimensions, mm

(according to GOST 8338 - 75)

bearing no.	d	D	B	r	bearing no.	d	D	B	r
				0,5					3,5
				1,0					4,0
				2,0					5,0
				2,0					5,0
				3,0					6,0
				3,0					1,5

Parameter is an independent or interrelated quantity that characterizes any product or phenomenon (process) as a whole or their individual properties. Parameters define the technical characteristics of a product or process, mainly in terms of performance, basic dimensions, design.

Quantitatively, the geometric parameters of parts are evaluated by means of linear dimensions.

The size- numerical value of a linear quantity (diameter, length, etc.) in the selected units of measurement (in mechanical engineering, as a rule, in millimeters).

By purpose, the dimensions are divided into dimensions that determine the size and shape of the part, and coordinating dimensions. Coordinating dimensions (for parts of complex shape and in nodes) determine the relative position of the critical surfaces of the parts necessary for the correct operation of the mechanism or their position relative to certain surfaces of lines and points, called constructive bases.

When processing the surface, the parts are coordinated relative to the technological bases, and when measuring, they are coordinated relative to the measuring bases. In this case, the principle of unity of bases is important. From these dimensions, functional dimensions are distinguished - that is, dimensions that directly affect the performance of machines and service functions of components and parts, and technological dimensions that are necessary directly for the manufacture of the part and its control.

Nominal size - the size obtained by the calculation method according to one of the performance criteria (strength, stiffness, etc.), selected from design, technological, operational, aesthetic and other considerations. This size serves as the starting point for deviations, and the limiting dimensions are determined relative to it. For the parts that make up the connection, it is common, and is called the nominal size of the connection.

The nominal dimensions obtained by calculation are rounded so that they correspond to the values of the series of normal linear dimensions. The series of normal linear dimensions (Renard series) are built on the basis of the preferred numbers, which are decimal series, geometric progressions with denominators = 1.6 for the R 5 series; = 1.25 for the R10 series; -1.12 for row R 20; =1.06 for the R 40 series. When choosing, preference is given to a series with a larger gradation, i.e. row R5 should be preferred to row R 10, etc.

The actual size is the size established by the measurement with the allowable error. In order for a product to meet its intended purpose, its dimensions must be maintained between two allowable sizes, the difference of which forms a tolerance.

The two maximum allowable sizes, between which the actual size must be or one of which can be equal, are called the limit sizes. The larger of the two size limits is called the largest size limit, and the smaller is called the smallest size limit. The nominal size of the hole is indicated by the Latin capital letter D max and D min, shaft - d max and d min. (See fig.1).

Comparison of the actual size with the limit dimensions gives an idea of the suitability of the part, for which GOST 25346-82 establishes the concept of through and non-through size limits. The maximum material limit or through limit is the maximum amount of material, namely the largest shaft size limit and the smallest hole size limit.

The minimum material limit or impassable limit is the minimum amount of metal, namely the smallest shaft size limit and the largest hole size limit.

For convenience, the nominal size of the part is indicated, and each of the two limiting sizes is determined by its deviation from this nominal size. The absolute value and the sign of the deviation are obtained by subtracting the nominal size from the corresponding limit size.

About Hole

Rice. 1.1. Tolerance fields of the hole and shaft when landing with a clearance (hole deviations are positive, shaft deviations are negative).

Limit deviations are divided into upper and lower. The upper limit deviation of the hole ES and the shaft es is the algebraic difference between the largest limit and nominal dimensions, the lower limit deviation of the hole EI and the shaft ei is the algebraic difference between the smallest limit and nominal dimensions.

For hole: ES = D max – D,

For the shaft: es = d max - d,

ei = dmin – d.

Deviation is positive, if the limit size is greater than the nominal one, and negative if the limit size is less than the nominal one.

On engineering drawings, the nominal, limiting dimensions and their deviations are indicated in mm, without indicating units, for example:

Angular dimensions and their maximum deviations are given in degrees, minutes and seconds, with units indicated, for example 42 0 30’25”.

Limit deviations in the tolerance tables are indicated in micrometers. If the absolute values of the deviations are equal, they are indicated once with the sign () next to the nominal size, for example, 60 0.2.

A deviation equal to 0 is not indicated on the drawings, only one deviation is applied - positive in place of the upper or negative in place of the lower limit deviation, for example 200 +0.2; 200 -0.2

The difference between the largest and smallest limit sizes or the absolute value of the algebraic difference between the upper and lower deviations is called the size tolerance (T). The tolerance is always positive. It determines the specified manufacturing accuracy. With its increase, the quality of the part deteriorates, and the cost decreases.

To simplify, tolerances can be displayed graphically as tolerance fields. In this case, the axis of the product is always located under the diagram. Tolerance field - a field limited by upper and lower deviations. The tolerance field is determined by the tolerance value and its position relative to the nominal size. Zero line - a line corresponding to the nominal size, from which dimensional deviations are plotted in the graphic representation of tolerances and fits. With a horizontal zero line, positive deviations are plotted upwards from it, and negative deviations downwards.

Fig. 1.2 Tolerance fields of the hole and shaft

Connections.

Machines and mechanisms consist of parts that, in the process of work, must make relative movements or are in relative rest. In most cases, machine parts are certain combinations of geometric bodies limited by surfaces of the simplest shapes: flat, cylindrical, conical, etc.

Two parts, the elements of which are included in each other, form a connection. Such parts are called mating parts, and the surfaces of the connected elements are called mating surfaces. The surfaces of those elements that are not included in the connection with the surfaces of other parts are called non-mating surfaces. Connections are subdivided according to the geometric shape of the mating surfaces. The connection of parts having mating cylindrical surfaces with a circular cross section is called smooth cylindrical.

In the connection of elements of two parts, one of the elements is internal (female), the other is external (male). In the system of tolerances and fits of smooth joints, any external element is conditionally called a shaft, and any internal element is called a hole. These terms also apply to non-conjugated elements.

The difference in the dimensions of the hole and the shaft before assembly determines the nature of the connection of the parts, or fit, i.e., greater or lesser freedom of relative movement of the parts or the degree of resistance to their mutual displacement.

The difference between the hole and shaft sizes, if the hole size is larger than the shaft size, is called the gap S=D-d.

The difference between the dimensions of the shaft and the hole before assembly, if the size of the shaft is larger than the size of the hole, called interference N = d-D.

The gap characterizes the greater or lesser freedom of relative movement of the connection parts.

Preload - the degree of resistance to the mutual displacement of parts in the connection, i.e. the strength of their fixed connection.

If necessary, the clearance can be expressed as an interference fit with a (-) sign;

S \u003d (-N), and interference as a gap with a sign (-); N=(-S).

LECTURE #2

Methods for normalizing parameters in design.

Normalization steps:

–– choice of nominal value;

–– setting limit values or limit deviations

Rated values - are chosen based on the requirements for strength, rigidity, kinematic accuracy of the machine, etc.

Limit values - are assigned to ensure the normal operation of mates of 2 or more parts (in dimensional chains).

Normalization methods:

–– research: provides the correctness and quality of the solution for new problems; very costly.

– analog method: used for trivial problems. Provides time savings. Based on experience - calculation of fits with clearance, interference, rolling bearings, etc.

On the working drawing of machine parts, the designer puts down nominal size - a common size for all connected parts, determined based on strength, rigidity or design considerations. It serves as the starting point for deviations.

Can a designer make any size nominal?

In accordance with GOST 6636-69 "Normal linear dimensions" it must be rounded up to those available in this GOST. Rows of normal linear dimensions are geometric progressions. There are four of them, they are designated Ra5, Ra10, Ra20, Ra40.

Ra5	Ra10	Ra20	Ra40

1,6	1,25	1,12	1,06

Preference is given to sizes from the rows with the largest gradation - the 5th row is the most preferable.

Reducing the number of sizes leads to a decrease in the sizes of cutting and measuring tools, dies, fixtures, and typification of technological processes is ensured.

Actual (true) size - the size that is obtained after the manufacture and measurement of the part, part, size with an allowable error.

d is the nominal size;

d d - the actual size, for the suitability of the part, it ranges from d max to d min:

These are the limit sizes.

Pass limit - limit size corresponding to the maximum amount of material (d max and D min)

impassable limit - limit size corresponding to the minimum amount of material (d min and D max)

Let's simplify the task. We will count the dimensions from one plane.

Limit contours have the form of a nominal surface (contour) and correspond to the largest d max and smallest d min dimensions of the part.

Lines of the limit contour of the part P.K

This drawing can be further simplified, because. the main task is to ensure the accuracy of the nominal size.

It can be seen from the figure that the largest allowable variation in dimensions is characterized by a tolerance.

Size tolerance - the difference between the largest and smallest limit sizes (T-Tolerance)

Hole tolerance

Shaft tolerance

The tolerance is always T>0. It determines the allowable variation in the dimensions of suitable parts in a batch. (Manufacturing tolerance)

Size deviation – difference between the size and the corresponding nominal size (E,e-ecart)

Lower deviation - the difference between the smallest limit and nominal sizes (I, i - inferieur):

hole shaft

Upper deviation - the difference between the largest limit and nominal size (S, s - superieur):

hole shaft

Lower and upper - limit deviations.

Actual deviation - algebraic difference between actual and nominal sizes:

hole shaft

Limit dimensions = nominal dimensions + deviation.

Hole

Tolerance field - the zone between the largest and smallest limit sizes, depicted graphically.

Zero line - a line on the tolerance field diagram corresponding to the nominal size or nominal contour.

We will postpone the deviations along the y-axis. These will be the coordinates relative to the zero line of the limit contours. Deviations can have a "+" and "-" sign, the tolerance field relative to the zero line will be located differently. (Shaft example)

The tolerance value can be determined through deviations:

Tolerance – algebraic difference of upper and lower deviation (>0)

Deviations can be e>0, e<0, е=0

Schematic representation of tolerance fields.

The construction of tolerance fields is carried out on a scale. Tolerance fields are shown as rectangles. Relative to the zero line, the rectangle is located in such a way that the upper side determines the upper deviation, the lower side determines the lower one. Deviations with signs are put down at the tops of the two right corners of the rectangles (µm). Graphically, the height of the rectangle represents the tolerance value. The length of the rectangle is arbitrary.

Zero line, defines the nominal size (in mm)

In directories d, D - in mm; deviations es, ei, ES, EJ and tolerances TD, Td in µm, 1 µm = 10 -6 m = 10-3 mm.

Example. Build a tolerance field and put down deviations, determine the limiting dimensions.

d = 40 mm; EJ=0; TD = 39 µm (H8); es = -25 µm; Td = 25 µm

Hole

The size- numerical value of a linear quantity (diameter, length, etc.) in the selected units of measurement.

There are actual, nominal and limit sizes.

actual size- the size established by measurement using a measuring instrument with a permissible measurement error.

The measurement error is the deviation of the measurement result from the true value of the measured quantity. true size- the size obtained as a result of manufacture and the value of which we do not know.

Nominal size- the size with respect to which the limiting dimensions are determined and which serves as the starting point for deviations.

The nominal size is indicated on the drawing and is common to the hole and shaft forming the connection and is determined at the product development stage based on the functional purpose of the parts by performing kinematic, dynamic and strength calculations, taking into account structural, technological, aesthetic and other conditions.

The nominal size thus obtained must be rounded up to the values established by GOST 6636-69 "Normal linear dimensions". The standard in the range from 0.001 to 20,000 mm provides for four main rows of sizes: Ra 5, Ra 10, Ra 20, Ra 40, as well as one additional row of Ra 80. In each row, the dimensions change according to the geometric profession with the following denominator values corresponding to the rows: (A geometric progression is a series of numbers in which each subsequent number is obtained by multiplying the previous one by the same number - the denominator of the progression.)

Each decimal interval for each row contains, respectively, the row number 5; ten; twenty; 40 and 80 numbers. When setting nominal sizes, preference should be given to rows with a larger gradation, for example, a row Ra 5 should be preferred to the row Ra 10 row Ra 10 - in a row Ra 20 etc. The series of normal linear dimensions are based on the series of preferred numbers (GOST 8032-84) with some rounding. For example, according to R5 (denominator 1.6), values 10 are taken; 16; 25; 40; 63; 100; 250; 400; 630 etc.

The standard for normal linear dimensions is of great economic importance, consisting in the fact that with a reduction in the number of nominal sizes, the required range of measuring cutting and measuring tools (drills, countersinks, reamers, broaches, gauges), dies, fixtures and other technological equipment is reduced. At the same time, conditions are created for organizing the centralized production of these tools and equipment at specialized machine-building plants.

The standard does not apply to technological interoperational dimensions and to dimensions associated with calculated dependencies with other accepted dimensions or dimensions of standard components.

Limit dimensions - two maximum allowable sizes between which the actual size must be or which may be equal.

When it is necessary to manufacture a part, the size must be given by two values, i.e. limit values. The larger of the two sizes is called the largest size limit and the smaller one smallest size limit. The size of a suitable part element must be between the largest and smallest allowable limit sizes.

To normalize the accuracy of a size means to indicate its two possible (permissible) size limits.

It is customary to designate the nominal, actual and limit sizes, respectively: for holes - D, D D, D max , D min ; for shafts - d, d D, d max , d mln .

Comparing the actual size with the limit ones, one can judge the suitability of the part element. The conditions of validity are the ratios: for holes D min D D; for shafts D min The limiting dimensions determine the nature of the connection of parts and their permissible manufacturing inaccuracy; in this case, the limiting dimensions may be greater or less than the nominal size or coincide with it.

Deviation- algebraic difference between the size (limit or actual) and the corresponding nominal size.

To simplify the sizing in the drawings, instead of limiting dimensions, limit deviations are affixed: upper deviation- algebraic difference between the largest limit and nominal sizes; lower deviation - algebraic difference between the smallest limit and nominal sizes.

The upper deviation is indicated ES(Ecart Superieur) for holes and es- for shafts; the lower deviation is indicated El(Ecart Interieur) for holes and ei- for shafts.

According to definitions: for holes ES=D max -D; EI=Dmin-D; for shafts es=d max -d; ei= d mln -d

The peculiarity of deviations is that they always have a sign (+) or (-). In a particular case, one of the deviations can be equal to zero, i.e. one of the limiting dimensions may coincide with the nominal value.

admission size is called the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations.

The tolerance is designated IT (International Tolerance) or T D - hole tolerance and T d - shaft tolerance.

According to the definition: hole tolerance T D =D max -D min ; shaft tolerance Td=d max -d min . Dimension tolerance is always a positive value.

The size tolerance expresses the spread of actual dimensions from the largest to the smallest limit dimensions, physically determines the amount of the officially permitted error of the actual size of the part element in the process of its manufacture.

Tolerance field is a field bounded by upper and lower deviations. The tolerance field is determined by the tolerance value and its position relative to the nominal size. With the same tolerance for the same nominal size, there may be different tolerance fields.

For a graphical representation of the tolerance fields, which makes it possible to understand the ratio of nominal and maximum dimensions, maximum deviations and tolerance, the concept of a zero line has been introduced.

Zero line the line corresponding to the nominal size is called, from which the maximum deviations of dimensions are plotted in the graphic representation of the tolerance fields. Positive deviations are laid up, and negative deviations are laid down from it (Fig. 1.4 and 1.5)

When assembling two parts that are included in one another, there are external-enclosing and internal-covered surfaces. One of the dimensions of the contacting surfaces is called the enclosing dimension, and the other is the covered dimension. For round bodies, the female surface is collectively called the hole, and the male surface is the shaft, and the corresponding dimensions are called the hole diameter and the shaft diameter.

A movable or fixed connection of parts can be made due to deviations of the mating dimensions of the shaft or hole in one direction or another from their nominal dimensions.

The estimated size affixed to the drawing is called the nominal size (Fig. 439). Nominal dimensions are given in millimeters.

Actual Size called the actual size obtained by direct measurement after processing the part.

limiting called the dimensions between which the actual size of the same element of the part of the manufactured batch can fluctuate. The larger one is called the largest size limit, and the smaller one is called the smallest size limit.

If the nominal size in the drawing has only one limit size, for example 25 +0.4 or 25 -0.1, then this means that the other limit size is the same as the nominal one. The plus sign indicates that the maximum size is greater than the nominal, and the minus sign indicates that the maximum size is less than the nominal.

Valid deviation is the difference between the actual and nominal sizes.

Upper deviation is the difference between the largest limit size and the nominal one.

lower deviation is the difference between the smallest limit and nominal sizes.

admission called the difference between the largest and smallest limit sizes.

Clearances, tensions and landings. Clearance is the positive difference between the size of the hole and the size of the shaft. The size of the gap determines the greater or lesser degree of freedom of the mutual movement of the mating parts.

An interference is a negative difference between the dimensions of the hole and the shaft, which creates (after assembly) a fixed connection.

landing called the nature or type of connection of two parts inserted one into the other.

All landings are divided into two groups: landings are mobile and landings are fixed.

rolling fit called the connection of two parts, ensuring the freedom of their relative movement.

Fixed landing is called the connection of two parts, providing an appropriate degree of strength of their connection.

There are the following types of landings, which differ from each other by a larger or smaller gap or a larger or smaller interference.

Movable landings Fixed landings

sliding with hot gr

Movements D Pressing Pr

Chassis X Easy-press plate

Easy-running L Blind G

Wide stroke W Tight

Tense H Dense R

Tolerance system. There are two tolerance systems: the hole system and the shaft system.

The hole system is characterized by the fact that in it for all landings of the same degree of accuracy (of the same class), referred to the same nominal diameter, the limiting dimensions of the hole remain constant. The implementation of various landings in the hole system is achieved by a corresponding change in the limiting dimensions of the shaft. In a hole system, the smallest hole size limit is its nominal size.

The shaft system is characterized by the fact that in it for all landings of the same system and degree of accuracy (of the same class), referred to the same nominal diameter, the limiting dimensions of the shaft remain constant. The implementation of various landings in the shaft system is achieved by a corresponding change in the limiting dimensions of the hole. In the shaft system, the largest shaft size limit is its nominal size.

The hole tolerance in the hole system is always directed in the direction of increasing the hole (into the body), and the shaft tolerance in the shaft system is always directed in the direction of decreasing the shaft (into the body). The base of the systems is indicated: the hole - by the letter A, the shaft - by the letter B. The hole in the shaft system and the shaft in the hole system are indicated by letters and numbers of the corresponding fit and accuracy class.

In mechanical engineering, the hole system is predominantly adopted.

5.1.3. The concept of dimensions and deviations

It is more convenient to consider the basic concepts of interchangeability in terms of geometric parameters using the example of shafts and holes and their connections.

Shaft - a term conventionally used to refer to the outer elements of parts, including non-cylindrical elements.

Hole - a term conventionally used to refer to the internal elements of parts, including non-cylindrical elements.

Quantitatively, the geometric parameters of parts are evaluated by means of dimensions.

Size - the numerical value of a linear quantity (diameter, length, etc.) in the selected units of measurement.

Dimensions are divided into nominal, actual and limit.

Definitions are given in accordance with GOST 25346-89 "Unified system of tolerances and landings. General provisions, series of tolerances and basic deviations."

The nominal size is the size against which deviations are determined.

The nominal size is obtained as a result of calculations (strength, dynamic, kinematic, etc.) or is selected from some other considerations (aesthetic, structural, technological, etc.). The size obtained in this way should be rounded to the nearest value from a series of normal sizes (see section "Standardization"). The main share of the numerical characteristics used in technology is linear dimensions. Due to the large proportion of linear dimensions and their role in ensuring interchangeability, series of normal linear dimensions have been established. Rows of normal linear dimensions are regulated in the entire range, which is widely used.

The basis for normal linear dimensions are the preferred numbers, and in some cases their rounded values.

The actual size is the element size set by the measurement. This term refers to the case when a measurement is made to determine the suitability of the dimensions of a part to specified requirements. Measurement is the process of finding the values of a physical quantity empirically using special technical means, and measurement error is the deviation of the measurement result from the true value of the measured quantity. True size - the size obtained as a result of processing the part. The value of the true size is unknown, since it is impossible to perform a measurement without error. In this regard, the concept of "true size" is replaced by the concept of "actual size".

Limit sizes - two maximum allowable sizes of the element, between which the actual size must be (or which may be equal to). For the limit size, which corresponds to the largest volume of material, i.e., the largest limit size of the shaft or the smallest limit size of the hole, the term maximum material limit is provided; for the limit size, which corresponds to the smallest volume of material, i.e., the smallest limit size of the shaft or the largest limit size of the hole, the limit of the minimum material.

Largest size limit - the largest allowable element size (Fig. 5.1)

Smallest size limit - the smallest allowable size of an element.

From these definitions it follows that when it is necessary to manufacture a part, its size must be given by two allowable values - the largest and the smallest. A suitable part must have a size between these limit values.

Deviation - the algebraic difference between the size (actual or limit size) and the nominal size.

The actual deviation is the algebraic difference between the actual and the corresponding nominal dimensions.

Limit deviation - the algebraic difference between the limit and nominal sizes.

Deviations are divided into upper and lower. The upper deviation E8, ea (Fig. 5.2) is the algebraic difference between the largest limit and nominal sizes. (ER is the upper deviation of the hole, er is the upper deviation of the shaft).

The lower deviation E1, e (Fig. 5.2) is the algebraic difference between the smallest limit and nominal sizes. (E1 - bottom deviation of the hole, e - bottom deviation of the shaft).

Tolerance T is the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations (Fig. 5.2).

Standard tolerance P - any of the tolerances established by this system of tolerances and landings.

Tolerance characterizes the accuracy of the size.

Tolerance field - a field limited by the largest and smallest limit sizes and determined by the tolerance value and its position relative to the nominal size. With a graphical representation, the tolerance field is enclosed between two lines corresponding to the upper and lower deviations relative to the zero line (Fig. 5.2).

It is almost impossible to depict deviations and tolerances on the same scale with the dimensions of the part.

The so-called zero line is used to indicate the nominal size.

Zero line - a line corresponding to the nominal size, from which dimensional deviations are plotted in the graphic representation of tolerance and fit fields. If the zero line is located horizontally, then positive deviations are plotted upwards from it, and negative deviations downwards (Fig. 5.2).

Using the above definitions, the following characteristics of shafts and holes can be calculated.

Schematic designation of tolerance fields

For clarity, it is convenient to present all the considered concepts graphically (Fig. 5.3).

In the drawings, instead of limiting dimensions, limit deviations from the nominal size are affixed. Considering that deviations can

can be positive (+), negative (-) and one of them can be equal to zero, then there are five cases of the position of the tolerance field in a graphic image:

1) upper and lower deviations are positive;

2) the upper deviation is positive, and the lower one is zero;

3) the upper deviation is positive and the lower deviation is zero;

4) the upper deviation is zero, and the lower deviation is negative;

5) upper and lower deviations are negative.

On fig. 5.4, but the listed cases for the hole are given, and in fig. 5.4, b - for the shaft.

For the convenience of normalization, one deviation is distinguished, which characterizes the position of the tolerance field relative to the nominal size. This deviation is called the main one.

The main deviation is one of two limit deviations (upper or lower), which determines the position of the tolerance field relative to the zero line. In this system of tolerances and landings, the main deviation is the closest to the zero line.

From formulas (5.1) - (5.8) it follows that the requirements for dimensional accuracy can be normalized in several ways. You can set two limit sizes, between which there must be

a - holes; b- shaft

measures of fit parts; you can set the nominal size and two maximum deviations from it (upper and lower); you can set the nominal size, one of the limit deviations (upper or lower) and the size tolerance.

The surfaces along which parts are connected during assembly are called conjugated , the rest - incompatible, or free . Of the two mating surfaces, the female surface is called hole , and the covered shaft (Fig. 7.1).

In this case, in the designations of the parameters of the holes, capital letters of the Latin alphabet are used ( D, E, S), and shafts - lowercase ( d, e,s).

The mating surfaces are characterized by a common size called nominal connection size (D, d).

Valid part size is the size obtained during manufacture and measurement with an allowable error.

Limit dimensions are the maximum ( D max and d max) and minimum ( D min and d min ) allowable dimensions, between which the actual size of a suitable part must be located. The difference between the largest and smallest limit sizes is called admission hole size TD and shaft Td .

TD(Td)=D max (d max ) – D min (d min ).

The size tolerance determines the specified boundaries (limit deviations) of the actual size of the good part.

Tolerances are depicted as fields limited by the upper and lower size deviations. In this case, the nominal size corresponds to zero line . The deviation closest to the zero line is called main . The main deviation of the holes is indicated in capital letters of the Latin alphabet A, B, C, Z, shafts - lowercase a, b, c, … , z.

Hole tolerances TD and shaft Td can be defined as the algebraic difference between the upper and lower limit deviations:

TD(Td) = ES(es) – EI(ei).

The amount of tolerance depends on the size and the required level of precision in the manufacture of the part, which is determined by quality (degree of accuracy).

quality is a set of tolerances corresponding to the same degree of accuracy.

The standard establishes 20 qualifications in decreasing order of accuracy: 01; 0; one; 2…18. Qualities are indicated by a combination of capital letters IT with serial number of qualification: IT 01, IT 0, IT 1, …, IT 18. With an increase in the qualification number, the tolerance for the manufacture of a part increases.

The cost of manufacturing parts and the quality of the joint work depend on the correct appointment of the quality. The following are recommended areas for applying qualifications:

- from 01 to 5 - for standards, gauge blocks and gauges;

- from 6 to 8 - for the formation of landings of critical parts, widely used in mechanical engineering;

- from 9 to 11 - to create landings of irresponsible nodes operating at low speeds and loads;

- from 12 to 14 - for tolerances on free dimensions;

- from 15 to 18 - for tolerances on workpieces.

On the working drawings of parts, tolerances are affixed next to the nominal size. In this case, the letter specifies the main deviation, and the number specifies the degree of accuracy. For example:

 25d6;  25 H7;  30 h8 ;  30 F8 .

7.2. The concept of landings and landing systems

landing called the nature of the connection of two parts, determined by the freedom of their relative movement. Depending on the relative position of the tolerance fields, the hole and the landing shaft can be of three types.

1. With guaranteed clearance S on condition: D min ≥ d max :

- maximum clearance S max = D max – d min ;

- minimum clearance S min = D min – d max .

Landings with a gap are designed to form movable and fixed detachable connections. Provide ease of assembly-disassembly of nodes. In fixed connections, they require additional fastening with screws, dowels, etc.

2. With guaranteed tension N on condition: D max d min :

- maximum tension N max = d max – D min ;

- minimum tension N min = d min – D max .

Interference fits provide the formation of permanent connections more often without the use of additional fastening.

3. transitional landings , at which it is possible to obtain both a gap and an interference fit in the joint:

- maximum clearance S max = D max – d min ;

- maximum tension N max = d max – D min .

Transition fits are designed for fixed detachable connections. Provide high centering accuracy. Require additional fastening with screws, dowels, etc.

ESDP provides landings in the hole system and in the shaft system.

Landings in the hole system main hole H with different shaft tolerance fields: a, b, c, d, e, f, g, h(landing with a gap); j S , k, m, n(transitional landings); p, r, s, t, u, v, x, y, z(pressure landings).

Fits in the shaft system are formed by a combination of the tolerance field main shaft h with different hole tolerances: A, B, C, D, E, F, G, H(landing with a gap); J s , K, M, N(transitional landings); P, R, S, T, U, V, X, Y, Z(pressure landings).

Landings are put down on the assembly drawings next to the nominal size of the conjugation in the form of a fraction: in the numerator, the tolerance for the hole, in the denominator, the tolerance for the shaft. For example:

30 or 30

.

It should be noted that in the designation of the landing in the hole system in the numerator, the letter H, and in the shaft system in the denominator - the letter h. If the designation contains both letters H and h, for example  20 H6/h5 , then in this case the hole system is preferred.

It has been established by metrological practice that it is impossible to make absolutely exact dimensions of a part, and there is no need to always have a very accurate value of the size of the machined part.

It must be remembered that the more precisely the size must be processed, the more expensive the production. Apparently, it is not necessary to explain in particular that in various mechanisms and machines there are parts that must be processed with particular care, and there are parts for which careful manufacture is not required. Therefore, there is a need to talk about dimensional accuracy.

As in every case, with regard to dimensional accuracy, there are a number of concepts and definitions that are necessary in order to speak the same language and express your thoughts in a shorter way.

Consider a number of practically used definitions and concepts of dimensions and their deviations.

Size - the numerical value of a physical quantity obtained as a result of measuring a characteristic or parameter of an object (process) in the selected units of measurement. In most cases, it is the difference between the states of an object or process in terms of a selected parameter, characteristic, indicator over time compared to a measure, a standard, a true or actual value of a physical quantity.

Actual size - the size established by the measurement with an allowable error. The size is only then called valid when it is measured with an error that can be allowed by any regulatory document. This term refers to the case when a measurement is made to determine the suitability of the dimensions of an object or process for certain requirements. When such requirements are not established and measurements are not made for the purpose of product acceptance, the term measured size is sometimes used, i.e. the size obtained from the results of the measurement, instead of the term "actual size". In this case, the measurement accuracy is selected depending on the goal set before the measurement.

The true size is the size obtained as a result of processing, manufacturing, the value of which is unknown to us, although it exists, since it is impossible to measure completely without error. Therefore, the concept of "true size" is replaced by the concept of "actual size", which is close to the true one under the conditions of the goal.

Limit sizes are the maximum allowable sizes between which the actual size must be or which can be equal. From this definition, it can be seen that when it is necessary to manufacture a part, then its size should be given by two values, i.e. valid values. And these two values \u200b\u200bare called the largest limit size - the larger of the two limit sizes and the smallest limit size - the smaller of the two limit sizes. A suitable part must have a size between these limit sizes. However, specifying the requirements for manufacturing accuracy with two dimensions is very inconvenient when drawing up drawings, although in the USA this is how the size is specified. Therefore, in most countries of the world, the concepts of "nominal size", "deviations" and "tolerance" are used.

Nominal size - the size with respect to which the limit sizes are determined and which serves as the starting point for deviations. The size indicated on the drawing is nominal. The nominal size is determined by the designer as a result of calculations of overall dimensions or strength or stiffness, or taking into account design and technological considerations.

However, it is impossible to take for the nominal any size that turned out during the calculation.

It must be remembered that the economic efficiency of metrological support is achieved when it is possible to get by with a small range of sizes without compromising quality. So, if you imagine that the designer will put on the drawing any nominal size, for example, the size of the holes, then it will be practically impossible to produce drills centrally in tool factories, since there will be an infinite number of drill sizes.

In this regard, the industry uses the concepts of preferred numbers and series of preferred numbers, i.e. values to which calculated values should be rounded. Usually rounded up to the nearest higher. This approach makes it possible to reduce the number of standard sizes of parts and assemblies, the number of cutting tools and other technological and control equipment.

Rows of preferred numbers around the world are accepted the same and are geometric progressions with denominators W; “VWVW 4 VlO, which are approximately equal to 1.6; 1.25; 1.12; 1.06 (a geometric progression is a series of numbers in which each subsequent number is obtained by multiplying the previous one by the same number - the denominator of the progression). These series are provisionally named R5; RIO; R20; R40.

Preferred numbers are widely used in standardization when it is necessary to set a number of values of normalized parameters or properties within certain ranges. The nominal values of linear dimensions in existing standards are also taken from the indicated series of preferred numbers with a certain rounding. For example, according to R5 (denominator 1.6), values 10 are taken; 16; 25; 40; 63; 100; 160; 250; 400; 630 etc.

Deviation - the algebraic difference between the limit and the real, i.e. measured sizes. Therefore, the deviation should be understood as how much the size differs from the allowable value when normalizing the requirements or according to the results of the measurement.

Since, when normalizing according to permissible deviations, there are two limiting sizes - the largest and smallest, then the terms upper and lower deviations are accepted when normalizing tolerances, i.e. indications of requirements within the size tolerance. The upper deviation is the algebraic difference between the largest limit and nominal sizes. The lower deviation is the algebraic difference between the actual and the smallest limit sizes when normalized by the tolerance value.

The peculiarity of deviations is that they always have a sign, either plus or minus. An indication in the definition of an algebraic difference shows that both deviations, i.e. both upper and lower can have positive values, i.e. the largest and smallest limit sizes will be greater than the nominal, or minus values (both less than the nominal), or the upper deviation may have a plus, and the lower - a minus deviation.

At the same time, there may be cases when the upper deviation is greater than the nominal one, then the deviation will take a plus sign, and the lower deviation is less than the nominal one, then it has a minus sign.

The upper deviation is indicated by ES at the holes and es at the shafts, and sometimes - BO.

The lower deviation is indicated by EI at the holes, ei at the shafts, or - BUT.

Tolerance (usually denoted T) - the difference between the largest and smallest limit sizes, or the absolute value of the algebraic difference between the upper and lower deviations. A feature of the tolerance is that it does not have a sign. This is, as it were, a zone of size values, between which the actual size must be, i.e. good part size.

Synonyms for this term can be as follows: "permissible value", "dimensions", "characteristic", "parameters".

If we are talking about a tolerance of 10 microns, then this means that in a batch of suitable parts there may be parts whose dimensions in the limiting case differ from each other by no more than 10 microns.

The concept of tolerance is very important and is used as a criterion for the accuracy of manufacturing parts. The smaller the tolerance, the more accurate the part will be made. The larger the tolerance, the coarser the detail. But at the same time, the smaller the tolerance, the more difficult, more complicated and hence the more expensive the manufacture of parts; the larger the tolerances, the easier and cheaper it is to manufacture the part. So there is a certain contradiction between developers and manufacturers. Designers want tolerances to be small (more accurate product) and manufacturers want tolerances to be large (easier to manufacture).

Therefore, the choice of tolerance must be justified. In all cases, where possible, large tolerances should be used, as this is economically beneficial for production, provided that the quality of the output product does not deteriorate.

Very often, along with the term "tolerance" and instead of it (not quite right), the term "tolerance field" is used, since, as mentioned above, tolerance is a zone (field) within which the dimensions of a good part are located.

The tolerance field, or the field of the permissible value, is a field limited by the upper and lower deviations. The tolerance field is determined by the tolerance value and its position relative to the nominal size.

Basic concepts of tolerances and landings

The mechanisms of machines and devices consist of parts that perform certain relative movements in the process of work or are connected motionlessly. Details that interact to some extent in a mechanism are called conjugated.
Absolutely accurate manufacturing of any part is impossible, just as it is impossible to measure its absolute size, since the accuracy of any measurement is limited by the capabilities of measuring instruments at this stage of scientific and technological progress, while there is no limit to this accuracy. However, the execution of parts of mechanisms with the highest accuracy is often impractical, primarily from an economic point of view, since high-precision products are much more expensive to manufacture, and for normal functioning in a mechanism, it is quite enough to make a part with less accuracy, i.e. cheaper.

Production experience has shown that the problem of choosing the optimal accuracy can be solved by setting for each part size (especially for its mating sizes) the limits within which its actual size can fluctuate; at the same time, it is assumed that the assembly, which includes the part, must correspond to its purpose and not lose its operability under the required operating conditions with the necessary resource.

Recommendations for the choice of maximum deviations in the dimensions of parts have been developed on the basis of many years of experience in the manufacture and operation of various mechanisms and devices and scientific research, and are set out in a unified system of tolerances and fits (ESDP SEV). Tolerances and landings established ESDP CMEA
Consider the basic concepts of this system.

The nominal size is called the main size, obtained from the calculation of strength, rigidity, or selected structurally and affixed to the drawing. Simply put, the nominal size of the part is obtained by designers and developers by calculation. (based on the requirements of strength, rigidity, etc.) and is indicated on the detail drawing as the main dimension.
The nominal connection size is common to the hole and shaft that make up the connection. According to nominal dimensions, drawings of parts, assembly units and devices are performed on one scale or another.

For unification and standardization, series of nominal sizes are established (GOST 8032-84 "Preferred numbers and series of preferred numbers"). The calculated or selected size should be rounded to the nearest value from the standard range. This especially applies to the dimensions of parts obtained with a standard or normalized tool, or connecting in relation to other standard parts or assemblies.
To reduce the range of cutting and measuring tools used in production, it is first of all recommended to use sizes ending in 0 and 5 and then on 0; 2; 5 and 8 .

The size obtained as a result of measuring the part with the greatest possible accuracy is called the actual one.
Do not confuse the actual size of a part with its absolute size.
Absolute size - the real (actual) size of the part; it cannot be measured by any ultra-precise measuring instruments, since there will always be an error, primarily due to the level of development of science, engineering and technology. In addition, any material body at a temperature above absolute zero "breathes" - microparticles, molecules and atoms are constantly moving on its surface, breaking away from the body and returning back. Therefore, even with ultra-precise measuring instruments at our disposal, it is impossible to determine the absolute size of the part; one can only talk about the real size in an infinitely small segment (moment) of time.
The conclusion is obvious - the absolute size of the part (as well as any body) is an abstract concept.

The dimensions between which the actual size of the manufactured part can be located are called the limit, while the largest and smallest limit sizes are distinguished.
A part made in the interval between the limiting dimensions is considered suitable. If its size goes beyond the limit - it is considered a marriage.
According to the limiting dimensions, the type of connection of parts and the permissible inaccuracy of their manufacture are established.
For convenience, the drawings indicate the nominal size of the part, and each of the two limiting sizes is determined by its deviation from this size. The value and sign of the deviation is obtained by subtracting the nominal size from the corresponding limit size.

The difference between the largest limit and nominal dimensions is called the upper deviation (denoted es or ES), the difference between the smallest limit and nominal - the lower deviation (denoted ei or EI).
The upper deviation corresponds to the largest limit size, and the lower one to the smallest.

All mating (interacting) in the mechanism, parts are divided into two groups - shafts and holes.
The shaft denotes the outer (male) element of the part. In this case, the shaft does not have to have a round shape: the concept of “shaft” includes, for example, a key, and the keyway in this case is called a “hole”. The main shaft is called, the upper deviation of which is equal to zero.
The dimensions of the shaft in the diagrams and in the calculations are indicated by lowercase (small) letters: d, dmax, dmin, es, ei, etc.

A hole designates an inner (female) feature of a part. As in the case of the shaft, the hole does not have to be round - its shape can be any. The main hole is called the hole, the lower deviation of which is zero.
The dimensions of the hole in the diagrams and in the calculations are indicated in capital (capital) letters: D, Dmax, Dmin, ES, EI, etc.

Tolerance (T) is the difference between the largest and smallest limit dimensions of the part. That is, tolerance is the interval between the maximum dimensions, within which the part is not considered a marriage.
Shaft size tolerance is denoted Td, holes - TD. Obviously, the larger the dimensional tolerance, the easier it is to manufacture the part.
The dimensional tolerance of a part can be defined as the difference between the limit sizes or as the sum of the limit deviations:

TD(d) = D(d)max – D(d)min = ES(es) + EI(ei) ,

in this case, the signs of limit deviations should be taken into account, since the tolerance on the size of the part is always positive (cannot be less than zero).

Landings

The nature of the connection, determined by the difference between the female and male dimensions, is called fit.
The positive difference between the diameters of the hole and the shaft is called clearance. (denoted by the letter S), and negative - interference (denoted by the letter N).
In other words, if the shaft diameter is less than the hole diameter, there is a gap, but if the shaft diameter exceeds the hole diameter, there is interference in the interface.
The gap determines the nature of the mutual mobility of the mating parts, and the tightness determines the nature of their fixed connection.

Depending on the ratio of the actual dimensions of the shaft and the hole, movable landings are distinguished - with a gap, fixed landings - with an interference fit and transitional landings, i.e., landings in which both a gap and an interference may be present (depending on what deviations have the actual dimensions of the mating parts from the nominal dimensions).
Landings in which a gap is necessarily present are called landings with a guaranteed gap, and landings in which an interference is required - with a guaranteed interference.
In the first case, the limiting dimensions of the hole and the shaft are chosen in such a way that there is a guaranteed gap in the interface.
The difference between the largest hole size limit (Dmax) and the smallest shaft size limit (dmin) determines the largest gap (Smax) :

Smax \u003d Dmax - dmin.

The difference between the smallest hole size limit (Dmin) and the largest shaft size limit (dmax) - the smallest gap (Smin) :

Smin \u003d Dmin - dmax.

The actual gap will be between the specified limits, i.e. between the maximum and minimum gap. The gap is necessary to allow movement of the connection and the placement of grease. The higher the number of revolutions and the higher the viscosity of the lubricant, the larger the gap should be.

In interference fits, the limiting dimensions of the shaft and hole are chosen in such a way that there is a guaranteed interference in the interface, limited by the minimum and maximum values \u200b\u200b- Nmax and Nmin:

Nmax = dmax – Dmin , Nmin = dmin – Dmax .

Transitional fit and may give a small amount of clearance or interference. Before the parts are made, it is impossible to say what will be in conjugation. It only becomes clear when assembling. The clearance should not exceed the value of the largest clearance, and the preload - the value of the maximum preload. Transition fits are used when it is necessary to ensure the exact centering of the hole and shaft.
Total in ESDP CMEA provided 28 types of basic deviations for shafts and the same number for holes. Each of them is indicated by a lowercase Latin letter (GOST 2.304 - 81) if the deviation refers to the shaft, or an uppercase letter if the deviation refers to the hole.
The letter designations of the main deviations are taken in alphabetical order, starting from the deviations that provide the largest gaps in the joint. A combination of various deviations of the shaft and the hole can be used to obtain landings of a different nature. (clearance, tightness or transitional).

Fits in hole system and shaft system

Landings set ESDP CMEA, can be implemented by hole or shaft systems.

The hole system is characterized by the fact that in it for all landings the limiting dimensions of the hole remain constant, and the landings are carried out by a corresponding change in the limiting dimensions of the shaft (i.e. the shaft is fitted to the bore). The size of the hole is called the main, and the size of the shaft is called the landing.

The shaft system is characterized by the fact that in it for all landings the limiting dimensions of the shaft remain constant, and the landings are carried out by changing the hole (i.e. the hole is adjusted to fit the shaft). The size of the shaft is called the main one, and the holes are called the landing.

In industrial enterprises, the hole system is mainly used, since it requires fewer cutting and measuring tools, i.e., it is more economical. In addition, it is technologically more convenient to fit the shaft to the hole, and not vice versa, since it is more convenient to process and control measurements of the outer surface, rather than the inner one.
The shaft system is usually used for the outer rings of ball bearings and in cases where several parts with different fits are mounted on a smooth shaft.

In mechanical engineering, the most common landings are arranged in descending order of tightness and increasing clearance: press (Pr), lightly pressed (Pl), deaf (G), tight (T), tense (N), dense (P), slip (S), movement (D), running (X), easy running (L), wide running (W).
Press fits give a guaranteed tight fit. Deaf, tight, tense and tight landings are transitional, and the rest have a guaranteed gap.
For a slip fit, the guaranteed clearance is zero.

To assess the accuracy of connections (landings), they use the concept of landing tolerance, which is understood as the difference between the largest and smallest gaps (in landings with a gap) or the largest and smallest tightness (in tight landings). In transitional landings, the landing tolerance is equal to the difference between the largest and smallest interferences or the sum of the largest interference and the largest clearance.
The fit tolerance is also equal to the sum of the tolerances of the hole and the shaft.

qualifications

The set of tolerances corresponding to the same degree of accuracy for all nominal sizes is called quality (I). In other words, quality is the degree of accuracy with which a part is made, while taking into account the size of this part.
Obviously, if a very large and a very small part are made with the same tolerance, then the relative accuracy of manufacturing a large part will be higher. Therefore, the system of qualifications takes into account the fact that (with the same tolerances) the ratio of the tolerance to the nominal size of a large part will be less than the ratio of the tolerance to the nominal size of a small part (Fig. 2), i.e., a conditionally large part is made more accurately with respect to their sizes. If, for example, for a shaft with a nominal diameter of 3 meters, a millimeter deviation from the size can be considered insignificant, then for a shaft with a diameter of 10 mm, such a deviation will be very noticeable.
The introduction of a system of qualifications avoids such confusion, since the accuracy of manufacturing parts is tied to their dimensions.

By ESDP CMEA qualifications are standardized in the form 19 rows. Each qualification is indicated by a serial number 01; 0; 1; 2; 3;...; 17 , increasing with increasing tolerance.
The two most accurate qualifications - 01 and 0 .
Link to qualifications ESDP CMEA may be abbreviated with the letters IT "International Approval" followed by the qualification number.
For example, IT7 means tolerance for 7 -th qualification.

In the CMEA system, the following symbols are used to designate tolerances with an indication of qualifications:

The letters of the Latin alphabet are used, while the holes are defined in uppercase letters, and the shafts in lowercase.
Hole in hole system (main hole) denoted by the letter H and numbers - the number of the qualification. For example, H6, H11 etc.
The shaft in the hole system is indicated by the landing symbol and numbers - the quality number. For example, g6, d11 etc.
The conjugation of the hole and the shaft in the hole system is indicated fractionally: in the numerator - the hole tolerance, in the denominator - the shaft tolerance.

Graphic representation of tolerances and landings

For clarity, they often use a graphical representation of tolerances and landings using the so-called tolerance fields (see Fig. 3).

The construction is carried out as follows.
From the horizontal line, conditionally depicting the surface of the part at its nominal size, limit deviations are plotted on an arbitrarily chosen scale. Usually, on the diagrams, the deviations are indicated in microns, but tolerance fields can also be built in millimeters if the deviations are large enough.

The line, which, when constructing schemes of tolerance fields, corresponds to the nominal size and serves as the starting point for dimensional deviations, is called zero (0-0) .
Tolerance field - a field limited by upper and lower deviations, that is, with a graphical representation of the tolerance field, zones are shown that are limited by two lines drawn at distances corresponding to the upper and lower deviations on the selected scale.
Obviously, the tolerance field is determined by the tolerance value and its position relative to the nominal size.
On the diagrams, the tolerance fields have the form of rectangles, the upper and lower sides of which are parallel to the zero line and display the maximum deviations, and the sides in the selected scale correspond to the size tolerance.

The diagrams indicate the nominal D and limit (Dmax, Dmin, dmax, dmin) dimensions, limit deviations (ES, EI, es, ei) tolerance fields and other parameters.

The maximum deviation, which is closer to the zero line, is called the main (top or bottom). It defines the position of the tolerance field relative to the zero line. For tolerance fields located below the zero line, the upper deviation is the main one.
For tolerance fields located above the zero line, the main one is the lower deviation.

The principle of formation of tolerance fields, adopted in ESDP, allows a combination of any major deviations with any qualifications. For example, you can create tolerance fields a11, u14, c15 and others not specified in the standard. The exception is the main deviations J and j , which are replaced by the main deviations Js , and js .

The use of all major deviations and qualifications allows you to get 490 tolerance fields for shafts and 489 for holes. Such wide possibilities for the formation of tolerance fields allow the use of ESDP in various special cases. This is its essential merit. However, in practice, the use of all tolerance fields is uneconomical, as it will cause an excessive variety of landings and special technological equipment.

When developing national systems of tolerances and landings based on systems ISO from the whole variety of tolerance fields, only those fields are selected that provide the needs of the country's industry and its foreign economic relations.

h and H - the upper and lower deviations of the shaft and the hole, equal to zero (tolerances with basic deviations h and H are taken for the main shafts and holes).
a - h (A - H) - deviations that form tolerance fields for landings with gaps.
js - n (Js - N) - deviations that form the tolerance fields of transitional landings.
p - zc (P - ZC) - deviations forming tolerance fields for interference fits.

Schematically, the main deviations are shown in Fig. four .

The tolerance field in the ESDP CMEA is formed by a combination of one of the main deviations with a tolerance for one of the qualifications. In accordance with this, the tolerance field is indicated by the letter of the main deviation and the quality number, for example 65f6; 65e11- for the shaft; 65P6; 65H7- for the hole.
The main deviations depend on the nominal dimensions of the parts and remain constant for all qualifications. The exception is the main deviations of the holes J, K, M, N and shafts j and k, which, with the same nominal sizes, in different qualifications have different values. Therefore, on the diagrams of the tolerance field with deviations J, K, M, N, j, k, usually divided into parts and shown as stepped.

Type specific tolerance fields js6, js8, js9 etc. They actually do not have a main deviation, since they are located symmetrically with respect to the zero line. By definition, the main deviation is the deviation closest to the zero line. This means that both deviations of such specific tolerance fields can be recognized as basic, which is unacceptable.

Of particular importance are the main deviations H and h, which are equal to zero (figure). Tolerance fields with such basic deviations are located from the face value "into the body" of the part; they are called the tolerance fields of the main hole and the main shaft.
Landing designations are constructed as fractions, and in the numerator there is always the designation of the tolerance field of the female surface (hole), and in the denominator - the tolerance field of the covered (shaft).

When choosing the quality of the connection and the type of fit, the designer should take into account the nature of the interface, operating conditions, the presence of vibration, service life, temperature fluctuations and manufacturing costs.
It is recommended to choose the quality and type of landing by analogy with those parts and assemblies whose work is well known, or be guided by the recommendations of reference literature and regulatory documents (OSTs).
In accordance with the quality of fit, the surface finish of the mating parts is selected.

Tolerances and fits are established for four ranges of nominal sizes:

small - before 1 mm;
medium - from 1 before 500 mm;
big - from 500 before 3150 mm;
very large - from 3150 before 10 000 mm.

The middle range is the most important because it is used much more frequently.

Designation of tolerances in the drawings

Indications and designations on the drawings of the maximum deviations of the shape and location of surfaces are regulated by GOST 2.308-79, which provides for these purposes special signs and symbols.
The main provisions of this standard, the signs and symbols used to indicate limit deviations, can be found in this document ( WORD format, 400 kB).