Qualities form the basis of the current system of admissions and landings. Quality represents a certain set of tolerances that, when applied to all nominal sizes, correspond to the same degree of accuracy.

Thus, we can say that it is the quality that determines how accurately the product as a whole or its individual parts is manufactured. The name of this technical term comes from the word " qualitas", which in Latin means " quality».

The set of tolerances that correspond to the same level of accuracy for all nominal sizes is called the qualification system.

The standard establishes 20 qualifications – 01, 0, 1, 2...18 . As the quality number increases, the tolerance increases, i.e., the accuracy decreases. Qualities from 01 to 5 are intended primarily for calibers. For landings, qualifications from 5th to 12th are provided.

Numerical tolerance values
Interval nominal sizes mm		Quality
		01	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
St.	Before	µm													mm
	3	0.3	0.5	0.8	1.2	2	3	4	6	10	14	25	40	60	0.10	0.14	0.25	0.40	0.60	1.00	1.40
3	6	0.4	0.6	1	1.5	2.5	4	5	8	12	18	30	48	75	0.12	0.18	0.30	0.48	0.75	1.20	1.80
6	10	0.4	0.6	1	1.5	2.5	4	6	9	15	22	36	58	90	0.15	0.22	0.36	0.58	0.90	1.50	2.20
10	18	0.5	0.8	1.2	2	3	5	8	11	18	27	43	70	110	0.18	0.27	0.43	0.70	1.10	1.80	2.70
18	30	0.6	1	1.5	2.5	4	6	9	13	21	33	52	84	130	0.21	0.33	0.52	0.84	1.30	2.10	3.30
30	50	0.6	1	1.5	2.5	4	7	11	16	25	39	62	100	160	0.25	0.39	0.62	1.00	1.60	2.50	3.90
50	80	0.8	1.2	2	3	5	8	13	19	30	46	74	120	190	0.30	0.46	0.74	1.20	1.90	3.00	4.60
80	120	1	1.5	2.5	4	6	10	15	22	35	54	87	140	220	0.35	0.54	0.87	1.40	2.20	3.50	5.40
120	180	1.2	2	3.5	5	8	12	18	25	40	63	100	160	250	0.40	0.63	1.00	1.60	2.50	4.00	6.30
180	250	2	3	4.5	7	10	14	20	29	46	72	115	185	290	0.46	0.72	1.15	1.85	2.90	4.60	7.20
250	315	2.5	4	6	8	12	16	23	32	52	81	130	210	320	0.52	0.81	1.30	2.10	3.20	5.20	8.10
315	400	3	5	7	9	13	18	25	36	57	89	140	230	360	0.57	0.89	1.40	2.30	3.60	5.70	8.90
400	500	4	6	8	10	15	20	27	40	63	97	155	250	400	0.63	0.97	1.55	2.50	4.00	6.30	9.70
500	630	4.5	6	9	11	16	22	30	44	70	110	175	280	440	0.70	1.10	1.75	2.80	4.40	7.00	11.00
630	800	5	7	10	13	18	25	35	50	80	125	200	320	500	0.80	1.25	2.00	3.20	5.00	8.00	12.50
800	1000	5.5	8	11	15	21	29	40	56	90	140	230	360	560	0.90	1.40	2.30	3.60	5.60	9.00	14.00
1000	1250	6.5	9	13	18	24	34	46	66	105	165	260	420	660	1.05	1.65	2.60	4.20	6.60	10.50	16.50
1250	1600	8	11	15	21	29	40	54	78	125	195	310	500	780	1.25	1.95	3.10	5.00	7.80	12.50	19.50
1600	2000	9	13	18	25	35	48	65	92	150	230	370	600	920	1.50	2.30	3.70	6.00	9.20	15.00	23.00
2000	2500	11	15	22	30	41	57	77	110	175	280	440	700	1100	1.75	2.80	4.40	7.00	11.00	17.50	28.00
2500	3150	13	18	26	36	50	69	93	135	210	330	540	860	1350	2.10	3.30	5.40	8.60	13.50	21.00	33.00

System of admissions and landings

A set of tolerances and fits, which is created on the basis theoretical research and experimental research, and also built on the basis of practical experience, is called a system of tolerances and landings. Its main purpose is to select tolerances and fits for typical joints of various machine and equipment parts that are minimally necessary but completely sufficient.

The basis for standardization of measuring instruments and cutting tools constitute exactly the most optimal gradations of tolerances and fits. In addition, thanks to them, the interchangeability of various parts of machines and equipment is achieved, as well as improving the quality of the finished product.

To design a unified system of tolerances and landings, tables are used. They indicate reasonable values ​​of maximum deviations for various nominal sizes.

Interchangeability

When designing various machines and mechanisms, developers proceed from the fact that all parts must meet the requirements of repeatability, applicability and interchangeability, as well as be unified and meet accepted standards. One of the most rational ways fulfillment of all these conditions is to use at the design stage the largest possible number of such components, the production of which has already been mastered by industry. This allows, among other things, to significantly reduce development time and costs. At the same time, it is necessary to ensure high accuracy interchangeable components, assemblies and parts in terms of their compliance with geometric parameters.

With this technical method, as a modular layout, which is one of the methods of standardization, it is possible to effectively ensure the interchangeability of units, parts and assemblies. In addition, it significantly facilitates repairs, which greatly simplifies the work of the relevant personnel (especially in difficult conditions), and allows you to organize the supply of spare parts.

Modern industrial production focused mainly on mass production of products. One of his mandatory conditions is the timely arrival on the assembly line of such components of finished products that do not require additional adjustment for their installation. In addition, interchangeability must be ensured that does not affect the functional and other characteristics of the finished product.

To main

section four

Tolerances and landings.
Measuring tool

Chapter IX

Tolerances and landings

1. The concept of interchangeability of parts

In modern factories, machine tools, cars, tractors and other machines are produced not in units or even in tens or hundreds, but in thousands. With such a production scale, it is very important that each part of the machine fits exactly into its place during assembly without any additional fitting. It is equally important that any part entering the assembly allows its replacement by another of the same purpose without any damage to the operation of the entire finished machine. Parts that satisfy such conditions are called interchangeable.

Interchangeability of parts- this is the property of parts to take their places in units and products without any preliminary selection or adjustment in place and perform their functions in accordance with the prescribed technical conditions.

2. Mating parts

Two parts that are movably or stationarily connected to each other are called mating. The size by which these parts are connected is called mating size. Dimensions for which parts are not connected are called free sizes. An example of mating dimensions is the diameter of the shaft and the corresponding diameter of the hole in the pulley; an example of free sizes would be outside diameter pulley

To obtain interchangeability, the mating dimensions of the parts must be accurately executed. However, such processing is complex and not always practical. Therefore, technology has found a way to obtain interchangeable parts while working with approximate accuracy. This method is for various conditions The work of a part establishes the permissible deviations of its dimensions, under which flawless operation of the part in the machine is still possible. These deviations, calculated for various operating conditions of the part, are built in a specific system called admission system.

3. Concept of tolerances

Size specifications. The calculated size of the part, indicated on the drawing, from which deviations are measured, is called nominal size. Typically, nominal dimensions are expressed in whole millimeters.

The size of the part actually obtained during processing is called actual size.

The dimensions between which the actual size of a part can fluctuate are called extreme. Of these, the larger size is called largest size limit, and the smaller one - smallest size limit.

Deviation is the difference between the maximum and nominal dimensions of a part. In the drawing, deviations are usually indicated by numerical values ​​at a nominal size, with the upper deviation indicated above and the lower deviation below.

For example, in size, the nominal size is 30, and the deviations will be +0.15 and -0.1.

The difference between the largest limit and nominal sizes is called upper deviation, and the difference between the smallest limit and nominal sizes is lower deviation. For example, the shaft size is . In this case, the largest limit size will be:

30 +0.15 = 30.15 mm;

the upper deviation will be

30.15 - 30.0 = 0.15 mm;

the smallest size limit will be:

30+0.1 = 30.1 mm;

the lower deviation will be

30.1 - 30.0 = 0.1 mm.

Manufacturing approval. The difference between the largest and smallest limit sizes is called admission. For example, for a shaft size, the tolerance will be equal to the difference in the maximum dimensions, i.e.
30.15 - 29.9 = 0.25 mm.

4. Clearances and interference

If a part with a hole is mounted on a shaft with a diameter , i.e., with a diameter under all conditions less than the diameter of the hole, then a gap will necessarily appear in the connection of the shaft with the hole, as shown in Fig. 70. In this case, landing is called mobile, since the shaft can rotate freely in the hole. If the shaft size is i.e. always larger size holes (Fig. 71), then when connecting the shaft will need to be pressed into the hole and then the connection will turn out preload

Based on the above, we can draw the following conclusion:
the gap is the difference between the actual dimensions of the hole and the shaft when the hole is larger than the shaft;
interference is the difference between the actual dimensions of the shaft and the hole when the shaft is larger than the hole.

5. Fit and accuracy classes

Landings. Plantings are divided into mobile and stationary. Below we present the most commonly used plantings, with their abbreviations given in parentheses.

Accuracy classes. It is known from practice that, for example, parts of agricultural and road machines can be manufactured less accurately than parts of lathes, cars, etc. without harming their operation. measuring instruments. In this regard, in mechanical engineering, parts of different machines are manufactured in tens various classes accuracy. Five of them are more accurate: 1st, 2nd, 2a, 3rd, Za; two are less accurate: 4th and 5th; the other three are rough: 7th, 8th and 9th.

To know what accuracy class the part needs to be manufactured in, on the drawings next to the letter indicating the fit, a number indicating the accuracy class is placed. For example, C 4 means: sliding landing of the 4th accuracy class; X 3 - running landing of the 3rd accuracy class; P - tight fit of 2nd accuracy class. For all 2nd class landings, the number 2 is not used, since this accuracy class is used especially widely.

6. Hole system and shaft system

There are two systems for arranging tolerances - the hole system and the shaft system.

The hole system (Fig. 72) is characterized by the fact that for all fits of the same degree of accuracy (same class), assigned to the same nominal diameter, the hole has constant maximum deviations, while a variety of fits is obtained by changing the maximum shaft deviations.

The shaft system (Fig. 73) is characterized by the fact that for all fits of the same degree of accuracy (same class), referred to the same nominal diameter, the shaft has constant maximum deviations, while the variety of fits in this system is carried out within by changing the maximum deviations of the hole.

In the drawings, the hole system is designated by the letter A, and the shaft system by the letter B. If the hole is made according to the hole system, then the nominal size is marked with the letter A with a number corresponding to the accuracy class. For example, 30A 3 means that the hole must be processed according to the hole system of the 3rd accuracy class, and 30A - according to the hole system of the 2nd accuracy class. If the hole is machined using the shaft system, then the nominal size is marked with a fit and the corresponding accuracy class. For example, a hole 30С 4 means that the hole must be processed with maximum deviations according to the shaft system, according to a sliding fit of the 4th accuracy class. In the case when the shaft is manufactured according to the shaft system, the letter B and the corresponding accuracy class are indicated. For example, 30B 3 will mean processing a shaft using a 3rd accuracy class shaft system, and 30B - using a 2nd accuracy class shaft system.

In mechanical engineering, the hole system is used more often than the shaft system, since it is associated with lower costs for tools and equipment. For example, to process a hole of a given nominal diameter with a hole system for all fits of one class, only one reamer is required and to measure a hole - one / limit plug, and with a shaft system, for each fit within one class a separate reamer and a separate limit plug are needed.

7. Deviation tables

To determine and assign accuracy classes, fits and tolerance values, special reference tables are used. Since permissible deviations are usually very small values, in order not to write extra zeros, in tolerance tables they are indicated in thousandths of a millimeter, called microns; one micron is equal to 0.001 mm.

As an example, a table of the 2nd accuracy class for a hole system is given (Table 7).

The first column of the table gives the nominal diameters, the second column shows the hole deviations in microns. The remaining columns show various fits with their corresponding deviations. The plus sign indicates that the deviation is added to the nominal size, and the minus sign indicates that the deviation is subtracted from the nominal size.

As an example, we will determine the fit movement in a hole system of the 2nd accuracy class for connecting a shaft with a hole with a nominal diameter of 70 mm.

The nominal diameter 70 lies between the sizes 50-80 placed in the first column of the table. 7. In the second column we find the corresponding hole deviations. Therefore, the largest limit hole size will be 70.030 mm, and the smallest 70 mm, since the lower deviation is zero.

In the column “Motion fit” against the size from 50 to 80, the deviation for the shaft is indicated. Therefore, the largest maximum shaft size is 70-0.012 = 69.988 mm, and the smallest maximum size is 70-0.032 = 69.968 mm.

Table 7

Limit deviations of the hole and shaft for the hole system according to the 2nd accuracy class
(according to OST 1012). Dimensions in microns (1 micron = 0.001 mm)

Control questions 1. What is called the interchangeability of parts in mechanical engineering?
2. Why are permissible deviations in the dimensions of parts assigned?
3. What are nominal, maximum and actual sizes?
4. Can the maximum size be equal to the nominal size?
5. What is called tolerance and how to determine tolerance?
6. What are the upper and lower deviations called?
7. What is clearance and interference called? Why are clearance and interference provided in the connection of two parts?
8. What types of landings are there and how are they indicated on the drawings?
9. List the accuracy classes.
10. How many landings does the 2nd accuracy class have?
11. What is the difference between a bore system and a shaft system?
12. Will the hole tolerances change for different fits in the hole system?
13. Will the maximum shaft deviations change for different fits in the hole system?
14. Why is the hole system used more often in mechanical engineering than the shaft system?
15. How they are marked on the drawings symbols deviations in hole dimensions if parts are made in a hole system?
16. In what units are the deviations indicated in the tables?
17. Determine using the table. 7, deviations and tolerance for the manufacture of a shaft with a nominal diameter of 50 mm; 75 mm; 90 mm.

Chapter X

Measuring tool

To measure and check the dimensions of parts, a turner has to use various measuring tools. For not very accurate measurements, they use measuring rulers, calipers and bore gauges, and for more accurate ones - calipers, micrometers, gauges, etc.

1. Measuring ruler. Calipers. Bore gauge

Yardstick(Fig. 74) is used to measure the length of parts and ledges on them. The most common steel rulers are from 150 to 300 mm long with millimeter divisions.

The length is measured by directly applying a ruler to the workpiece. The beginning of the divisions or the zero stroke is combined with one of the ends of the part being measured and then the stroke on which the second end of the part falls is counted.

Possible measurement accuracy using a ruler is 0.25-0.5 mm.

Calipers (Fig. 75, a) are the simplest tool for rough measurements of the external dimensions of workpieces. The caliper consists of two curved legs, which sit on the same axis and can rotate around it. Having spread the legs of the calipers slightly larger than the size being measured, lightly tapping them on the part being measured or some hard object moves them so that they come into close contact with the outer surfaces of the part being measured. The method of transferring the size from the part being measured to the measuring ruler is shown in Fig. 76.

In Fig. 75, 6 shows a spring caliper. It is adjusted to size using a screw and nut with a fine thread.

A spring caliper is somewhat more convenient than a simple caliper, as it maintains the set size.

Bore gauge. For rough measurements internal dimensions The bore gauge shown in Fig. is used. 77, a, as well as a spring bore gauge (Fig. 77, b). The device of the bore gauge is similar to that of a caliper; Measurement with these instruments is also similar. Instead of a bore gauge, you can use calipers by moving its legs one after the other, as shown in Fig. 77, v.

The measurement accuracy with calipers and bore gauges can be increased to 0.25 mm.

2. Vernier caliper with reading accuracy 0.1 mm

The accuracy of measurement with a measuring ruler, calipers, or bore gauge, as already indicated, does not exceed 0.25 mm. A more accurate tool is a caliper (Fig. 78), which can be used to measure both the external and internal dimensions of the workpieces. When working on a lathe, calipers are also used to measure the depth of a recess or shoulder.

The caliper consists of a steel rod (ruler) 5 with divisions and jaws 1, 2, 3 and 8. Jaws 1 and 2 are integral with the ruler, and jaws 8 and 3 are integral with frame 7, sliding along the ruler. Using screw 4, you can secure the frame to the ruler in any position.

To measure the outer surfaces use jaws 1 and 8, to measure the internal surfaces use jaws 2 and 3, and to measure the depth of the recess use rod 6 connected to frame 7.

On frame 7 there is a scale with strokes for reading fractional fractions of a millimeter, called vernier. The vernier allows measurements to be made with an accuracy of 0.1 mm (decimal vernier), and in more accurate calipers - with an accuracy of 0.05 and 0.02 mm.

Vernier device. Let's consider how a vernier reading is made on a vernier caliper with an accuracy of 0.1 mm. The vernier scale (Fig. 79) is divided into ten equal parts and occupies a length equal to nine divisions of the ruler scale, or 9 mm. Therefore, one division of the vernier is 0.9 mm, i.e. it is shorter than each division of the ruler by 0.1 mm.

If you close the jaws of the caliper closely, the zero stroke of the vernier will exactly coincide with the zero stroke of the ruler. The remaining vernier strokes, except the last one, will not have such a coincidence: the first vernier stroke will not reach the first stroke of the ruler by 0.1 mm; the second stroke of the vernier will not reach the second stroke of the ruler by 0.2 mm; the third stroke of the vernier will not reach the third stroke of the ruler by 0.3 mm, etc. The tenth stroke of the vernier will exactly coincide with the ninth stroke of the ruler.

If you move the frame so that the first stroke of the vernier (not counting the zero) coincides with the first stroke of the ruler, then between the jaws of the caliper you will get a gap of 0.1 mm. If the second stroke of the vernier coincides with the second stroke of the ruler, the gap between the jaws will already be 0.2 mm, if the third stroke of the vernier coincides with the third stroke of the ruler, the gap will be 0.3 mm, etc. Consequently, the vernier stroke that exactly coincides with which - using a ruler stroke, shows the number of tenths of a millimeter.

When measuring with a caliper, they first count a whole number of millimeters, which is judged by the position occupied by the zero stroke of the vernier, and then look at which vernier stroke coincides with the stroke of the measuring ruler, and determine tenths of a millimeter.

In Fig. 79, b shows the position of the vernier when measuring a part with a diameter of 6.5 mm. Indeed, the zero line of the vernier is between the sixth and seventh lines of the measuring ruler, and, therefore, the diameter of the part is 6 mm plus the reading of the vernier. Next, we see that the fifth stroke of the vernier coincides with one of the strokes of the ruler, which corresponds to 0.5 mm, so the diameter of the part will be 6 + 0.5 = 6.5 mm.

3. Vernier depth gauge

For measuring the depth of recesses and grooves, as well as for determining correct position ledges along the length of the roller, a special tool called depth gauge(Fig. 80). The design of the depth gauge is similar to that of a caliper. Ruler 1 moves freely in frame 2 and is fixed in it in the desired position using screw 4. Ruler 1 has a millimeter scale, on which, using vernier 3, located on frame 2, the depth of the recess or groove is determined, as shown in Fig. 80. The reading on the vernier is carried out in the same way as when measuring with a caliper.

4. Precision caliper

For work performed with greater accuracy than those considered so far, use precision(i.e. accurate) calipers.

In Fig. 81 shows a precision caliper from the plant named after. Voskov, having a measuring ruler 300 mm long and a vernier.

The length of the vernier scale (Fig. 82, a) is equal to 49 divisions of the measuring ruler, which is 49 mm. This 49 mm is precisely divided into 50 parts, each equal to 0.98 mm. Since one division of the measuring ruler is equal to 1 mm, and one division of the vernier is equal to 0.98 mm, we can say that each division of the vernier is shorter than each division of the measuring ruler by 1.00-0.98 = 0.02 mm. This value of 0.02 mm indicates that accuracy, which can be provided by the vernier of the considered precision caliper when measuring parts.

When measuring with a precision caliper, to the number of whole millimeters passed by the zero stroke of the vernier, one must add as many hundredths of a millimeter as the vernier stroke that coincides with the stroke of the measuring ruler shows. For example (see Fig. 82, b), along the ruler of the caliper, the zero stroke of the vernier passed 12 mm, and its 12th stroke coincided with one of the strokes of the measuring ruler. Since matching the 12th line of the vernier means 0.02 x 12 = 0.24 mm, the measured size is 12.0 + 0.24 = 12.24 mm.

In Fig. 83 shows a precision caliper from the Kalibr plant with a reading accuracy of 0.05 mm.

The length of the vernier scale of this caliper, equal to 39 mm, is divided into 20 equal parts, each of which is taken as five. Therefore, against the fifth stroke of the vernier there is the number 25, against the tenth - 50, etc. The length of each division of the vernier is

From Fig. 83 it can be seen that with the caliper jaws closed tightly, only zero and finishing touches verniers coincide with the strokes of the ruler; the rest of the vernier strokes will not have such a coincidence.

If you move frame 3 until the first stroke of the vernier coincides with the second stroke of the ruler, then between the measuring surfaces of the caliper jaws you will get a gap equal to 2-1.95 = 0.05 mm. If the second stroke of the vernier coincides with the fourth stroke of the ruler, the gap between the measuring surfaces of the jaws will be equal to 4-2 X 1.95 = 4 - 3.9 = 0.1 mm. If the third stroke of the vernier coincides with the next stroke of the ruler, the gap will be 0.15 mm.

The counting on this caliper is similar to that described above.

A precision caliper (Fig. 81 and 83) consists of ruler 1 with jaws 6 and 7. Markings are marked on the ruler. Frame 3 with jaws 5 and 8 can be moved along ruler 1. A vernier 4 is screwed to the frame. For rough measurements, frame 3 is moved along ruler 1 and, after securing with screw 9, a count is taken. For accurate measurements, use the micrometric feed of the frame 3, consisting of a screw and nut 2 and a clamp 10. Having clamped the screw 10, by rotating the nut 2, feed the frame 3 with a micrometric screw until the jaw 8 or 5 comes into close contact with the part being measured, after which a reading is made.

5. Micrometer

The micrometer (Fig. 84) is used to accurately measure the diameter, length and thickness of the workpiece and gives an accuracy of 0.01 mm. The part to be measured is located between the fixed heel 2 and the micrometric screw (spindle) 3. By rotating the drum 6, the spindle moves away or approaches the heel.

To prevent the spindle from pressing too hard on the part being measured when the drum rotates, there is a safety head 7 with a ratchet. By rotating the head 7, we will extend the spindle 3 and press the part against the heel 2. When this pressure is sufficient, with further rotation of the head its ratchet will slip and a ratcheting sound will be heard. After this, the rotation of the head is stopped, the resulting opening of the micrometer is secured by turning the clamping ring (stopper) 4, and a count is taken.

To produce readings, a scale with millimeter divisions divided in half is applied on the stem 5, which is integral with the 1 micrometer bracket. Drum 6 has a beveled chamfer, divided along the circumference into 50 equal parts. The bars from 0 to 50 are marked with numbers every five divisions. At the zero position, i.e. when the heel is in contact with the spindle, the zero stroke on the chamfer of the drum 6 coincides with the zero stroke on the stem 5.

The micrometer mechanism is designed in such a way that with a full rotation of the drum, spindle 3 will move by 0.5 mm. Consequently, if you turn the drum not a full turn, that is, not by 50 divisions, but by one division, or part of a revolution, then the spindle will move by This is the precision of the micrometer. When counting, they first look at how many whole millimeters or whole and a half millimeters the drum on the stem has opened, then add to this the number of hundredths of a millimeter that coincides with the line on the stem.

In Fig. 84 on the right shows the size taken with a micrometer when measuring the part; countdown needs to be done. The drum has opened 16 whole divisions (half not open) on the stem scale. The seventh stroke of the chamfer coincided with the line of the stem; therefore, we will have another 0.07 mm. The total reading is 16 + 0.07 = 16.07 mm.

In Fig. Figure 85 shows several micrometer measurements.

It should be remembered that a micrometer is a precision instrument that requires careful handling; therefore, when the spindle lightly touches the surface of the part being measured, you should no longer rotate the drum, but to further move the spindle, rotate head 7 (Fig. 84) until the sound of a ratchet follows.

6. Bore gauges

Bore gauges (shtihmas) are used for precise measurements of the internal dimensions of parts. There are permanent and sliding bore gauges.

Constant or hard, the bore gauge (Fig. 86) is a metal rod with measuring ends having a spherical surface. The distance between them is equal to the diameter of the hole being measured. To exclude the influence of the heat of the hand holding the bore gauge on its actual size, the bore gauge is equipped with a holder (handle).

Micrometric bore gauges are used to measure internal dimensions with an accuracy of 0.01 mm. Their design is similar to that of a micrometer for external measurements.

The head of the micrometric bore gauge (Fig. 87) consists of a sleeve 3 and a drum 4 connected to a micrometric screw; screw pitch 0.5 mm, stroke 13 mm. The sleeve contains a stopper 2 and a heel/with a measuring surface. By holding the sleeve and rotating the drum, you can change the distance between the measuring surfaces of the bore gauge. Readings are made like a micrometer.

The measurement limits of the shtihmas head are from 50 to 63 mm. To measure large diameters (up to 1500 mm), extensions 5 are screwed onto the head.

7. Limit measuring instruments

In the serial production of parts according to tolerances, the use of universal measuring instruments(calipers, micrometer, micrometric bore gauge) is impractical, since measurement with these instruments is a relatively complex and time-consuming operation. Their accuracy is often insufficient, and, in addition, the measurement result depends on the skill of the worker.

To check whether the dimensions of the parts are within precisely established limits, use a special tool - maximum calibers. The gauges for checking shafts are called staples, and those for checking holes are called traffic jams.

Measuring with limit clamps. Double-sided limit bracket(Fig. 88) has two pairs of measuring cheeks. The distance between the cheeks of one side is equal to the smallest maximum size, and the other - to the largest maximum size of the part. If the shaft being measured extends to the larger side of the bracket, then its size does not exceed the permissible limit, and if not, then its size is too large. If the shaft also passes to the smaller side of the bracket, then this means that its diameter is too small, i.e. less than permissible. Such a shaft is a defect.

The side of the staple with the smaller size is called impassable(stamped “NOT”), the opposite side with a large size - checkpoint(branded “PR”). The shaft is considered suitable if the bracket, lowered onto it by the go-through side, slides down under the influence of its weight (Fig. 88), and the non-go-through side does not rest on the shaft.

To measure large-diameter shafts, instead of double-sided clamps, single-sided clamps are used (Fig. 89), in which both pairs of measuring surfaces lie one after the other. The front measuring surfaces of such a bracket are used to check the largest permissible diameter of the part, and the rear ones are used to check the smallest. These staples are lighter and significantly speed up the inspection process, since it is enough to apply the staple once to measure.

In Fig. 90 shown adjustable limit bracket, in which, if worn, the correct dimensions can be restored by rearranging the measuring pins. In addition, such a clamp can be adjusted to specific dimensions and thus a large number of sizes can be checked with a small set of staples.

To rearrange to new size you need to loosen the locking screws 1 on the left leg, move the measuring pins 2 and 3 accordingly and fasten the screws 1 again.

They are widespread flat limit brackets(Fig. 91), made of sheet steel.

Measuring with limit plugs. Cylindrical limit plug gauge(Fig. 92) consists of a go-through plug 1, a no-go plug 3 and a handle 2. The go-through plug (“PR”) has a diameter equal to the smallest permissible hole size, and the no-go plug (“NOT”) has the largest. If the “PR” plug passes, but the “NOT” plug does not pass, then the diameter of the hole is greater than the smallest limit and less than the largest, i.e., it is within the permissible limits. The pass-through plug is longer than the non-pass-through plug.

In Fig. Figure 93 shows the measurement of a hole with a limit plug on a lathe. The pass-through side should fit through the hole easily. If the non-passable side also enters the hole, then the part is rejected.

Cylindrical plug gauges for large diameters are inconvenient due to their large weight. In these cases, two flat plug gauges are used (Fig. 94), of which one has a size equal to the largest, and the second to the smallest permissible. The walk-through side is wider than the walk-through side.

In Fig. 95 shown adjustable limit plug. It can be adjusted to multiple sizes just like an adjustable limit bracket, or rebuilt right size worn measuring surfaces.

8. Resistance gauges and indicators

Reismas. To accurately check the correct installation of a part in a four-jaw chuck, on a square, etc., use Reismas.

Using a surface gauge, you can also mark the center holes at the ends of the part.

The simplest surface plan is shown in Fig. 96, a. It consists of a massive tile with a precisely machined bottom plane and a rod along which a slide with a scribe needle moves.

A gauge of a more advanced design is shown in Fig. 96, b. The gauge needle 3, using hinge 1 and clamp 4, can be brought with its tip to the surface being tested. Precise installation carried out by screw 2.

Indicator. To control the accuracy of processing on metal cutting machines, checking the processed part for ovality, taper, and an indicator is used to check the accuracy of the machine itself.

The indicator (Fig. 97) has a metal case 6 in the shape of a clock, which houses the mechanism of the device. A rod 3 with a tip protruding outward passes through the indicator body, always under the influence of a spring. If you press the rod from bottom to top, it will move in the axial direction and at the same time rotate the arrow 5, which will move along the dial, which has a scale of 100 divisions, each of which corresponds to the movement of the rod by 1/100 mm. When the rod moves 1 mm, hand 5 will make a full revolution around the dial. Arrow 4 is used to count whole revolutions.

When taking measurements, the indicator must always be rigidly fixed relative to the original measuring surface. In Fig. 97, and shown universal stand for attaching the indicator. Indicator 6 is secured to vertical rod 9 using rods 2 and 1 of couplings 7 and 8. Rod 9 is secured in groove 11 of prism 12 with a knurled nut 10.

To measure the deviation of a part from a given size, bring the tip of the indicator to it until it comes into contact with the surface being measured and note the initial reading of arrows 5 and 4 (see Fig. 97, b) on the dial. Then the indicator is moved relative to the surface being measured or the surface being measured relative to the indicator.

The deviation of the arrow 5 from its initial position will show the size of the convexity (depression) in hundredths of a millimeter, and the deviation of the arrow 4 in whole millimeters.

In Fig. Figure 98 shows an example of using the indicator to check the alignment of the centers of the headstock and tailstock. lathe. For a more accurate check, install a precision ground roller between the centers and an indicator in the tool holder. By bringing the indicator button to the surface of the roller on the right and noticing the indication of the indicator arrow, manually move the caliper with the indicator along the roller. The difference in the deviations of the indicator arrow in the extreme positions of the roller will show how much the tailstock body should be moved in the transverse direction.

Using the indicator, you can also check the end surface of a machined part. The indicator is fixed in the tool holder instead of the cutter and is moved along with the tool holder in the transverse direction so that the indicator button touches the surface being tested. The deviation of the indicator arrow will show the amount of runout of the end plane.

Control questions 1. What parts does a caliper with an accuracy of 0.1 mm consist of?
2. How does the vernier of a caliper with an accuracy of 0.1 mm work?
3. Set the dimensions on the caliper: 25.6 mm; 30.8 mm; 45.9 mm.
4. How many divisions does the vernier of a precision caliper have with an accuracy of 0.05 mm? The same, with an accuracy of 0.02 mm? What is the length of one vernier division? How to read the vernier readings?
5. Set the dimensions using a precision caliper: 35.75 mm; 50.05 mm; 60.55 mm; 75 mm.
6. What parts does a micrometer consist of?
7. What is the micrometer screw pitch?
8. How are measurements taken using a micrometer?
9. Set the dimensions using a micrometer: 15.45 mm; 30.5 mm; 50.55 mm.
10. In what cases are bore gauges used?
11. What are limit gauges used for?
12. What is the purpose of the passing and non-passing sides of the limit gauges?
13. What designs of limit brackets do you know?
14. How to check the correct size with a limit stopper? Limit bracket?
15. What is the indicator used for? How to use it?
16. How does a surface gauge work and what is it used for?

Applying tolerances and fits on drawings. The principle of interchangeability.

The tolerance zone is the field limited by the upper and lower deviations. The tolerance field is determined by the size of the tolerance and its position relative to the nominal size. In a graphical representation, it is concluded between the lines corresponding to the upper and lower deviations of the zero line.

When drawing dimensions with upper and lower deviations on drawings, certain rules must be followed:

Upper or lower deviations equal to zero are not indicated.

The number of characters in the upper and lower deviations is equalized; if necessary, to maintain a single number of characters, zeros are added to the right, for example Æ .

The upper and lower deviations are recorded in two lines, with the upper deviation placed above the lower one; the height of the deviation digits is approximately half that of the nominal size digits;

In the case of a symmetrical location of the tolerance field relative to the zero line, i.e. when the upper deviation is equal in absolute value to the lower deviation, but opposite in sign, their value is indicated after the sign ± in figures equal in height to the figures of the nominal size;

The tolerance field characterizes not only the magnitude of the tolerance, but also its location relative to the nominal size or zero line. It can be located above, below, symmetrically, one-sidedly and asymmetrically relative to the zero line. For clarity, in the drawings of parts above the dimension line after the nominal size, it is customary to indicate the upper and lower deviations in millimeters with their signs, and also for clarity, diagrams of the location of the tolerance field of the shaft or hole relative to the zero line are drawn; in this case, the upper and lower deviations are laid out in micrometers, and not in millimeters.

Landing- the nature of the connection of the part, determined by the size of the resulting gaps or interference. There are three teak plantings:

With a gap

with interference

transitional.

Note that the shaft and hole forming the fit have the same nominal size and differ in upper and lower deviations. For this reason, in the drawings above the dimension line, the fit is indicated after the nominal size by a fraction, in the numerators of which the maximum deviations for the hole are written, and in the denominator - similar data for the shaft.

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, is called interference N. Interference fit – This is a fit that provides interference in the connection, and the hole tolerance is located below the shaft tolerance.

Least N min and greatest N max interferences have important values for interference fit:

N min occurs in a connection if in the hole with the largest limiting size D max the shaft of the smallest maximum size will be pressed d min ;

N max occurs at the smallest limiting hole size D min and the largest maximum shaft size d max .

The difference between the sizes of the hole and the shaft before assembly, if the size of the hole is larger than the shaft hole, is called gap S. A fit that provides clearance in the connection and the hole tolerance is located above the shaft tolerance is called a clearance fit. It is characterized by the smallest S min and greatest S max clearances:

S min takes place in the connection of the hole with the shaft; it is formed if in the hole with the smallest maximum size D min, the shaft with the largest limit size will be installed d max;

S max occurs at the largest limiting hole size D max and the smallest maximum shaft size d min .

The difference between the largest and smallest clearances or the sum of the tolerances of the hole and shaft making up the joint is called landing clearance.

And a landing in which it is possible to obtain both clearance and interference is called transitional landing. IN in this case The tolerance fields of the hole and shaft overlap partially or completely.

Due to the inevitable fluctuation in the dimensions of the shaft and hole from the largest to the smallest values, when assembling parts, fluctuations in clearances and interference occur. The largest and smallest gaps, as well as interference, are calculated using formulas. And the smaller the fluctuation of gaps or interference, the higher the accuracy of fit.

The principle of interchangeability and

The design property of a component part of a product that allows it to be used instead of another without additional processing, while maintaining the specified quality of the product it is part of, is called interchangeability. With complete interchangeability, similar parts and products, for example, bolts, studs, can be manufactured and installed in “their places” without additional processing or pre-fitting.

Along with complete interchangeability, it is allowed to assemble products using methods of incomplete and group interchangeability, adjustment and fitting.

Incomplete interchangeability includes the assembly of products based on theoretical and probabilistic calculations.

With group interchangeability, parts manufactured on common machine tools with technologically met tolerances are sorted by size into several size groups; then check the assembly of parts of the same group number.

The regulation method involves the assembly with regulation of the position or dimensions of one or more individual, pre-selected parts of the product, called compensators.

The fitting method is the assembly of products with the fitting of one and the assembled parts. Interchangeability ensures high quality of products and reduces their cost, while contributing to the development of advanced technology and measuring technology. Without interchangeability, modern production is impossible. Interchangeability is based on standardization- finding solutions to recurring problems in the field of science, technology and economics, aimed at achieving the optimal degree of ordering in a certain area. Standardization is aimed at improving the management of the national economy, increasing the technical level and quality of products, etc. The main task of standardization is to create a system of normative and technical documentation that establishes requirements for standardization objects, mandatory for use in certain areas of activity. The most important regulatory and technical document of standardization is a standard developed on the basis of the achievements of domestic and foreign science, technology, and advanced technology and providing solutions that are optimal for the economic and social development of the country.

Tolerances and landings are standardized by state standards included in two systems: ESDP - “Unified System of Tolerances and Landings” and ONV - “Basic Standards of Interchangeability”. ESDP applies to tolerances and fits in the dimensions of smooth elements of parts and to fits formed when connecting these parts. ONV regulates the tolerances and fits of keyed, splined, threaded and conical connections, as well as gears and wheels.

Tolerances and fits are indicated on drawings, sketches, technological maps and other technological documentation. Based on tolerances and fits, technological processes for manufacturing parts and controlling their dimensions, as well as assembling products, are developed.

On the working drawing, the parts are marked with dimensions called nominal, maximum dimensional deviations and symbols of tolerance fields. The nominal hole size is indicated by D, and the nominal shaft size is d. In cases where the shaft and hole form one connection, the nominal size of the connection is taken as the total size of the shaft and hole, designated d(D). The nominal size is selected from a number of normal linear dimensions according to GOST 6636-69. limiting the number of sizes used. For sizes in the range 0.001-0.009 mm installed row: 0.001; 0.002; 0.003;..0.009 mm. There are four main rows of normal sizes (Ra5; Ra10; Ra20; Ra40) and one row of additional sizes. Rows with a larger gradation of sizes are preferable, i.e. row Ra5 will reduce to prefer a row Ra10 etc.

It is almost impossible to process a part exactly to its nominal size due to numerous errors affecting the processing web. The dimensions of the workpiece differ from the specified nominal size. Therefore, they are limited to two marginal sizes, one of which (larger) is called the largest maximum size, and the other (smaller) is called the smallest maximum size. The largest maximum hole size is indicated by D max, shaft d max; correspondingly the smallest maximum hole size D min, and shaft d min .

Measuring a hole or shaft with a permissible error determines its actual size. A part is suitable if its actual size is greater than the smallest limit size, but does not exceed the largest limit size.

In the drawings, instead of maximum dimensions, two maximum deviations are indicated next to the nominal size, for example .

Deviation is called the algebraic difference between the sizes and the corresponding nominal size. Thus, the nominal size also serves as the starting point for deviations and determines the position of the zero line.

Actual deviation– algebraic difference between real and nominal size.

Maximum deviation- algebraic difference between real and nominal sizes. One of the two maximum deviations is called upper, and the other is called lower.

The upper and lower deviations can be positive, i.e. with a plus sign, negative, i.e. with a minus sign, and equal to zero.

Zero line– a line corresponding to the nominal size, from which dimensional deviations are plotted when graphically depicting tolerances and fits (GOST 25346-82). If the zero line is located horizontally, then a positive deviation is laid up from it, and a negative one is laid down.

System of admissions and landings

ESDP standards apply to smooth mating and non-mating elements of parts with nominal dimensions up to 10,000 mm (Table 1)

Table 1 ESDP standards

Qualities

Classes (levels, degrees) of accuracy in the ESDP are called qualifications, which distinguishes them from accuracy classes in the OST system. Quality(degree of accuracy) - the level of gradation of system tolerance values.

Tolerances in each grade increase with increasing nominal dimensions, but they correspond to the same level of accuracy, determined by the grade (its serial number).

For a given nominal size, the tolerance for different grades is not the same, since each grade determines the need to use certain methods and means of processing products.

The ESDP establishes 19 qualifications, designated by a serial number: 01; 0; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; eleven; 12; 13; 14; 15; 16 and 17. The highest accuracy corresponds to quality 01, and the lowest - quality 17. The accuracy decreases from quality 01 to quality 17.

Quality tolerance is conventionally designated in capital Latin letters IT with the quality number, for example, IT6 - 6th quality tolerance. In what follows, the word tolerance refers to the tolerance of the system. Qualities 01, 0 and 1 are provided for assessing the accuracy of plane-parallel gauge blocks, and qualifications 2, 3 and 4 - for assessing smooth plug gauges and staple gauges. The dimensions of parts of high-precision critical connections, for example, rolling bearings, crankshaft journals, parts connected to rolling bearings of high accuracy classes, spindles of precision and precision metal-cutting machines and others are carried out according to the 5th and 6th qualifications. Qualities 7 and 8 are the most common. They are provided for the dimensions of precise critical connections in instrumentation and mechanical engineering, for example parts of internal combustion engines, automobiles, aircraft, metal-cutting machines, and measuring instruments. The dimensions of parts of diesel locomotives, steam engines, hoisting and transport mechanisms, printing, textile and agricultural machines are mainly carried out according to the 9th qualification. Quality 10 is intended for the dimensions of non-critical connections, for example, for the dimensions of parts of agricultural machines, tractors and wagons. The dimensions of parts forming non-critical connections, in which large gaps and their fluctuations are permissible, for example, the dimensions of covers, flanges, parts obtained by casting or stamping, are assigned according to the 11th and 12th qualifications.

Qualities 13-17 are intended for non-essential dimensions of parts that are not included in connections with other parts, i.e. for free dimensions, as well as for interoperational dimensions.

Tolerances in qualifications 5-17 are determined by the general formula:

1Tq = ai, (1)

Where q- number of qualifications; A- dimensionless coefficient established for each quality and not dependent on the nominal size (it is called the “number of tolerance units”); і - tolerance unit (µm) - a multiplier depending on the nominal size;

for sizes 1-500 µm

for sizes St. 500 to 10,000 mm

Where D With- geometric mean of boundary values

Where D min And D max– the smallest and largest limit value of the range of nominal sizes, mm.

For a given quality and range of nominal sizes, the tolerance value is constant for shafts and holes (their tolerance fields are the same). Starting from the 5th qualification, the tolerances when moving to an adjacent less accurate qualification increase by 60% (the denominator of the geometric progression is 1.6). After every five qualifications, tolerances increase 10 times. For example, for parts of nominal sizes St. 1 to 3 mm 5th qualification admission IT5 = 4 µm; after five qualifications it increases 10 times, i.e. IT1O =.40 µm etc.

Intervals of nominal sizes in the ranges of St. 3 to 180 and St. 500 to 10000 mm in the OST and ESDP systems they are the same.

In the OST system up to 3 mm The following size intervals are established: up to 0.01; St. 0.01 to 0.03; St. 0.03 to 0.06; St. 0.06 to 0.1 (exception); from 0.1 to 0.3; St. 0.3 to 0.6; St. 0.6 to 1 (exception) and from 1 to 3 mm. Interval St. 180 to 260 mm divided into two intermediate intervals: St. 180 to 220 and St. 220 to 260 mm. Interval -260 to 360 mm divided into intervals: St. 260 to 310 and St. 310 to 360 mm. Interval St. 360 to 500 mm divided into intervals: St. 360 to 440 and St. 440 to 500 mm.

When converting accuracy classes according to OST to qualifications according to ESDP, you need to know the following. Since in the OST system tolerances were calculated using formulas that differed from formulas (2) and (3), there is no exact match of tolerances for accuracy classes and qualifications. Initially, the OST system established accuracy classes: 1; 2; 2a; 3; 3a; 4; 5; 7; 8; and 9. Later, the OST system was supplemented with more accurate classes 10 and 11. In the OST system, the tolerances of shafts of accuracy classes 1, 2 and 2a are set smaller than for holes of the same accuracy classes.

This is due to the difficulty of processing holes compared to shafts.

Main deviations

Main deviation- one of two deviations (upper or lower), used to determine the position of the tolerance field relative to the zero line. This deviation is the closest deviation from the zero line. For tolerance fields of the shaft (hole) located above the zero line, the main deviation is the lower deviation of the shaft еѕ (for hole EI) with a plus sign, and for tolerance fields located below the zero line, the main deviation is the upper deviation of the shaft еѕ (for hole ES) with a minus sign. The tolerance zone begins from the main deviation boundary. The position of the second boundary of the tolerance field (i.e., the second maximum deviation) is determined as the algebraic sum of the value of the main deviation and the accuracy grade tolerance.

There are 28 main deviations for shafts and the same number of main deviations for holes (GOST 25346 - 82). The main deviations are indicated by one or two letters of the Latin alphabet: for the shaft - in lowercase letters from a to zc, and for the hole - in capital letters from A to ZC (Fig. 1, d). The values ​​of the main deviations are given in the tables.

The main deviations of the shafts from a to g (the upper deviations е* with a minus sign) and the main deviation of the shaft h (еs equal to zero) are intended to form tolerance fields for the shafts in fits with clearance; from ј (ј *) to n - in transitional fits from р to zс (lower deviations еі with a plus sign) - in interference fits. Similarly, the main deviations of the holes from A to G (lower deviations EI with a plus sign) and the main deviation of the hole H (for it EI = 0) are intended to form tolerance fields for holes in clearance fits; from Ј (Ј *) to N - in transitional fits and from P to ZС (upper deviations ES with a minus sign) - in interference fits. The letters ј * and Ј * indicate the symmetrical location of the tolerance relative to the zero line. In this case, the numerical values ​​of the upper еѕ (ЭЅ) and lower еі(ЭІ) deviation of the shaft (hole) are numerically equal, but opposite in sign (the upper deviation has a “plus” sign, and the lower one has a “minus” sign).

The main deviations of the shaft and holes, indicated by the letter of the same name (for a given size range), are equal in magnitude, but opposite in sign; they increase with increasing value of the size interval.

Hole system and shaft system

A combination of tolerance fields for shafts and holes can be obtained big number landing A distinction is made between fits in the hole system and in the shaft system.

Landings in the hole system- fits in which various gaps and interferences are obtained by connecting shafts of different sizes with one main hole (Fig. 1, a), the tolerance field of which (for a given quality and size range) is constant for the entire set of fits. The tolerance field of the main hole is located invariably relative to the zero

line so that its lower deviation EI = 0 (it is the main deviation H), and the upper deviation ES with a + “plus” sign is numerically equal to the tolerance of the main hole. The tolerance fields of the shafts in clearance fits are located below the zero line (under the tolerance field of the main hole), and in interference fits - above the tolerance field of the main hole (Fig. 1, b). In transitional fits, the tolerance fields of the shafts partially or completely overlap the tolerance field of the main hole.

Fittings in the shaft system- fits in which various gaps and interferences are obtained by connecting holes of different sizes to one main shaft, the tolerance field of which (for a given quality and size range) is constant for the entire set of fits. The tolerance field of the main shaft is located invariably relative to the zero line so that its upper deviation еѕ = 0, and the lower deviation еі with a “minus” sign is numerically equal to the tolerance of the main shaft. The tolerance fields of holes in clearance fits are located above the tolerance field of the main shaft, and in interference fits - below the tolerance field of the main shaft.

The hole system is characterized by a simpler technology for manufacturing products compared to the shaft system, and therefore it has received preferential use. The shaft system connects rolling bearings to the holes of the bushings or product bodies, as well as the piston pin to the piston and connecting rod, etc.

In some cases, to obtain connections with very large gaps, they use combined plantings- fits formed by the tolerance fields of holes from the shaft system and the tolerance fields of shafts from the hole system.

For nominal sizes less than 1 and St. 3150 mm, as well as for grades 9-12 with nominal sizes of 1-3150 mm, fits are formed by a combination of tolerance fields for holes and shafts of the same accuracy grade, for example, H6/p6; H7/e7; E8/h8; Н9/е9 and В11/h1. In the 6th and 7th grades with nominal sizes of 1-3150 mm, for technological reasons, it is recommended to select the hole tolerance field one grade coarser than the shaft tolerance field, for example, H7/k6; E8/h7.

In addition to the landings indicated in the tables, in technically justified cases, other landings formed from the ESDP tolerance fields are allowed for use. The fit must be related to the hole system or shaft system, and if the tolerances of the hole and shaft are unequal, the hole must have a larger tolerance. The tolerances of the hole and shaft can differ by no more than two grades.

The selection and assignment of tolerances and fits is carried out on the basis of calculations of the required clearances or interferences, taking into account the operating experience of such connections.