Designed calibers. Thread gauges - a special inspection tool
4. SMOOTH LIMIT CALIBERS
Calibers are called scaleless control instruments. They serve to control parts during the production process, i.e. to check whether the part size being executed is within specified tolerances. Using gauges, it is impossible to determine the numerical values of the value being tested; it is only possible to determine the suitability of the part, i.e. correspondence of actual values to given ones.
Working gauges are designed to control parts during their manufacturing process. They are used by equipment operators and adjusters, as well as quality control inspectors of the manufacturer.
Receiving gauges are used by customer representatives to accept parts.
Control gauges are used to check the sizes of working and receiving clamp gauges and to set the size of adjustable gauges.
A set of limit gauges for controlling the dimensions of smooth cylindrical parts consists of a go-through gauge (PR) and a non-go-through gauge (NOT). A part is considered suitable if the OL, under the influence of its own weight or a force approximately equal to it, passes along the controlled surface of the part, and does NOT pass.
4.1. Materials for calibers
Inserts and nozzles of plug gauges are made of steel X or ShKh-15. It is allowed to manufacture inserts and nozzles from U10A or U12A steel for all types of calibers, except for incomplete plug gauges obtained by stamping, as well as from steel 15 or 20 for calibers with a diameter of more than 10 mm.
The roughness parameters of the working surfaces must be within the range of Ra 0.04...0.32 microns, depending on the type of gauge, the accuracy of the controlled parameter of the product and its size.
To increase wear resistance and reduce costs in production conditions, gauges with inserts and nozzles made of carbide materials are often used. The wear resistance of such calibers is 50–150 times higher compared to the wear resistance of chrome-plated calibers, while the cost of the calibers increases by 3–5 times.
4.2. Gauge plugs
Smooth gauges for checking holes are made in the form of cylinders, i.e. are prototypes of the holes being tested, and are therefore called plugs. Both plugs - go-through and non-go-through - can be made as one piece if the hole diameter is less than 50 mm, and separately if it is larger (Figure 4.1).
Figure 4.1
If the PR gauge does not fit into the hole, then the part is considered unusable, but the defect is correctable, i.e. additional hole processing is required. If the plug does NOT fit into the hole, this means that the part is defective and cannot be corrected.
4.3. Gauge-staples
Smooth gauges for checking shafts are made in the form of brackets, and the brackets can be non-adjustable (Figure 4.2, a, b) and adjustable (Figure 4.2, c). If the clamp gauge PR does not pass along the shaft, then the defect is correctable, and if the clamp gauge does NOT pass along the shaft, then it is considered completely defective.
Gauge staples are one-sided (Figure 4.2, a, c) and double-sided (Figure 4.2, b). Adjustable staples with inserts or movable jaws (Figure 4.2, c) allow you to compensate for wear and can be adjusted to different sizes, however, they have lower accuracy and reliability compared to non-adjustable staples and, as a rule, are used to control dimensions with tolerances no more precise than 8- th quality of accuracy.
Figure 4.2
4.4. Control gauges
To control non-adjustable gauges and to install adjustable gauges, control gauges are used: for the through side (K-PR), non-go through (K-NOT) and for wear control (K-I). They are usually made in the form of washers (Figure 4.3). However, despite the small tolerance of control gauges, they distort the established tolerance fields for the manufacture and wear of working gauges, so control gauges have limited use. In small-scale and individual production, it is advisable to use gauge blocks or universal measuring instruments instead of control gauges.
Figure 4.3
4.5. Location of caliber tolerance fields
For smooth gauges, GOST 24853-81 establishes manufacturing tolerances: N – working gauge-plugs for holes; N 1 – clamp gauge for shafts; Нр – control gauges for staples. The diagram of tolerance fields for plugs is shown in Figure 4.4, and the diagram of tolerance fields for staples and control gauges is shown in Figure 4.5.
In grades 6, 8, 9, 10, tolerances H 1 for staples are approximately 50% greater than tolerances H for plugs of the corresponding grades, which is explained by the complexity of manufacturing staples. In grades 7, 11 and rougher, the tolerances N and N 1 are equal. Tolerances Нр for all types of control gauges are the same.
Figure 4.4
Figure 4.5
For pass-through gauges, which wear out more intensively during the inspection process compared to non-go-through gauges, in addition to the manufacturing allowance, a wear allowance is provided. For all pass-through gauges, the tolerance fields H and H 1 are shifted inside the product tolerance field by z and z 1 (for plugs and staples, respectively). Shifting tolerance fields and wear limits eliminates the possibility of distorting the nature of fits and guarantees obtaining the dimensions of suitable parts within the established tolerance fields.
The design size is indicated on the caliber drawings and documentation. This is the largest or smallest size of the caliber with one deviation equal to the tolerance, directed into the “body” of the caliber. On the drawing of the bracket, the smallest limit size with a positive deviation is indicated, for the plug and control gauge - their largest limit size with a negative deviation.
Limit sizes of calibers are calculated using the following formulas:
for cork -
for bracket –
for control -
5. DIMENSION CHAINS
A dimensional chain is a set of dimensions that form a closed contour and are directly involved in solving the problem. To indicate solutions to problems of ensuring the accuracy of dimensional chains, it is most convenient to represent them graphically in the form of a closed contour. For example, Figures 5.1, a and 5.2, a show sketches of the simplest part and assembly unit, and Figures 5.1, b and 5.2, b show dimensional chains consisting of the lengths of its elements.
Figure 5.1.
The sizes included in the chain are called constituent links or simply links, and are most often designated by capital letters of the Russian alphabet with indices. Sometimes lowercase letters of the Greek alphabet are used, except for the letters α, β, ε, λ, ω, ξ.
Figure 5.2.
In a dimensional chain, one link is always distinguished, which is called the closing link, and when solving some problems, the initial one. The closing link is the dimension (link) obtained last in the process of processing a part or assembling an assembly. In Figure 5.2, which shows a connection with a gap, the gap S itself will be a closing one. The closing link is usually designated by a letter with the index Δ, i.e. in Figure 5.2, b, instead of the designation B 3, you should put B Δ. According to the details shown in Figure 5.1, the issue can be resolved in two ways. If you sequentially process the dimensions A 2 and A 1, then the link A 3 will be the closing one, and if you first obtain the length A 3 and then process A 2, then the closing link will be A 1. The constituent links of the dimensional chain and the closing link are interconnected by an important pattern, which allows us to divide the constituent links into increasing and decreasing ones.
An increasing link in a dimensional chain is one whose increase increases the size of the closing link. The decreasing link will be the one with an increase in which the closing link decreases. So in Figure 5.3. link A1 is increasing, and links A2, A3, A4 will be decreasing.
Figure 5.3.
Accordingly, arrows are placed above the size designations: for increasing (A 1) it is directed to the right, and for decreasing (A 2 - A 4) it is directed to the left (Figure 5.3, b).
5.1. Classification of dimensional chains
Depending on the qualification characteristics, dimensional chains are divided into several types.
Depending on their location in the product, they can be detailed or assembled. If a closed circuit includes the dimensions of only one part, then such a chain is called sub-part (Figure 5.1), if the dimensions of several parts are included, then it is called an assembly chain (Figures 5.2 and 5.3).
According to the area of application, circuits are divided into design, technological and measuring. Design dimensional chains solve the problem of ensuring accuracy during design, and they establish a relationship between the dimensions of parts in the product. Figure 5.2, a shows an elementary assembly dimensional chain that solves the problem of ensuring the accuracy of the pairing of two parts, and in Figure 5.3, a - four parts.
Technological dimensional chains solve the problem of ensuring accuracy in the manufacture of parts at different stages of the technological process.
Measuring dimensional chains solve the problem of ensuring accuracy in measurement. They establish relationships between links that affect the accuracy of the measurement. When making measurements, the measuring instrument together with the auxiliary elements form a measuring dimensional chain, where the closing link is the size of the part element being measured.
Depending on the location of the links, dimensional chains are divided into linear, angular, flat and spatial. Chain dimensions whose links are linear dimensions are called linear. In such chains the links are located on parallel lines. In angular dimensional chains, the links represent angular dimensions, the deviations of which can be specified in linear quantities, related to the conventional length, or in degrees (radians). In a flat dimensional chain, the links are located arbitrarily in one or several parallel planes. In a spatial chain, the links are located arbitrarily, i.e. are not parallel to one another and are located in non-parallel planes.
5.2. Basic relationships of dimensional chains
The dimensional chain is always closed. Based on this property, a relationship has been established that connects the nominal dimensions of the links. For flat dimensional chains based on nominal values, this dependence is expressed by the formula:
, (5.1)
where m and n are the number of increasing and decreasing links, respectively.
To determine the relationship that connects the tolerances of links in a dimensional chain, you first need to determine the limit values of the original link. Obviously they will:
, (5.2)
, (5.3)
If we subtract the values of A Δmax and A Δmin, i.e. according to formulas 5.2 and 5.3 and taking into account the fact that the difference in the limit values is nothing more than a tolerance, the expression will be:
.
Finally you can get:
. (5.4)
From this formula it is clear that the tolerance value of the closing link is equal to the sum of the tolerances of the constituent links. Therefore, in order to ensure the greatest accuracy of the closing link, the dimensional chain should consist of as few links as possible, i.e. The principle of the shortest dimensional chain must be observed.
If you successively subtract from the expressions according to formulas 5.2 and 5.3 the expression according to formula 5.1, you will obtain dependencies by which the upper and lower limit deviations of the initial link are determined.
, (5.5)
, (5.6)
where E s and E i are the upper and lower maximum deviations of the corresponding links.
The coordinate of the middle of the tolerance field of the closing link is calculated as follows:
. (5.7)
The tolerance value in accordance with GOST 25346-89 for most qualifications is determined by the formula:
where T is a designation of tolerance without reference to a specific tolerance system and type of size;
a – the number of tolerance units determined for a given qualification;
i is a tolerance unit depending on the size.
In relation to calculations of the dimensional chain, it is better to write this formula in the following form:
Table 5.1
Values of a
Table 5.2
i values
5.3. Methods for calculating dimensional chains
5.3.1. Equal Tolerance Method
When calculating a chain using the equal tolerance method, it is assumed that all links are made with the same tolerances, i.e.
TA 1 = TA 2 = TA 3 = ... = TA n.
Formula (5.4) in this case can be represented as follows:
TA Δ = TA 1 + TA 2 + TA 3 +… + TA n.
If the tolerances are the same, then the TA Δ formula is written as follows:
. (5.10)
Maximum deviations are assigned taking into account the type of size: for female deviations are given as for the main holes, for male ones - as for the main shafts, for others - symmetrically.
However, the equal tolerance method is used relatively rarely, i.e. in cases where all nominal sizes fall within the same size range.
5.3.2. Equal tolerance method
This method involves performing all links of the chain with the same accuracy, i.e. one qualification at a time. This means that the values of a for all links will be the same, i.e.
Then the tolerance formula (5.4) can be written as follows:
From this dependence we can obtain a formula for determining a cf:
. (5.11)
If the dimensional chain contains links with predetermined calculations or standard tolerances (for example, rolling bearings), then these tolerances and i values are taken into account when determining a cf:
, (5.12)
where TA st is the tolerance established earlier;
k – number of links with predetermined tolerances.
According to the found a cf from the table. 5.2, the quality is selected, and from the table of tolerances for nominal sizes and a certain quality, tolerances for all links are found. Maximum deviations are assigned in the same way as for the equal tolerance method.
When calculating a chain using the probabilistic method, a cf is determined by the formula:
, (5.13)
where t is the risk coefficient, determined depending on the accepted or established percentage of defects p (Table 5.3);
λ i 2 – coefficient depending on the error distribution law. Most often, the error distribution is taken into account by the Gauss law, in this case λ i 2 = 1/9. But other distribution laws can also be used. If the size dispersion is close to Simpson’s law, then λ i 2 = 1/6, and if the nature of the size dispersion is unknown, then it is recommended to accept the law of equal probability with λ i 2 = 1/3.
Table 5.3
Risk coefficient values
5.4. Tasks and methods for calculating dimensional chains
Depending on the initial data and the accuracy of the links of the dimensional chain, as well as the chain for which the dimensions of the chain are determined, two problems are solved: direct and inverse.
The direct problem is solved to determine the tolerances and maximum deviations of the component links based on the given nominal values of all dimensions of the chain and the maximum deviations of the original (closing) link.
When solving the inverse problem, the nominal size, tolerance and maximum deviations of the initial link (closing) link are determined based on the given nominal values, tolerances and maximum deviations of the component links.
There are several methods for solving direct and inverse problems under conditions of complete and incomplete interchangeability. The most common methods are the following:
maximum – minimum;
probabilistic;
group interchangeability;
regulation;
fit and joint processing.
Moreover, complete interchangeability is ensured by only one method: maximum - minimum, therefore it has another name - the method of complete interchangeability.
5.4.1. Maximum-minimum method (full interchangeability)
The maximum-minimum method ensures the accuracy of the closing link for any combination of sizes of the component links. It is assumed that even with the most unfavorable combinations of link sizes (all increasing links have the largest values, and all decreasing links have the smallest, or vice versa), complete interchangeability will be ensured. Therefore, this method is sometimes called the method of complete interchangeability.
Depending on the goal, both direct and inverse problems can be solved and the method of equal or equal-precision tolerances can be used.
5.4.2. Probabilistic method
When calculating dimensional chains using the probabilistic method, the dimensional tolerances of the component links can be significantly expanded. This is explained by the fact that in most cases the dimensions of the closing link are subject to the law of normal distribution of errors, in which the risk of defects during assembly of the unit (0.27%) leads to a significant expansion of the tolerances of the component links.
Calculation of dimensional chains using the probabilistic method significantly reduces the cost of manufacturing parts, so it is advisable to use it in large-scale and mass production conditions.
5.4.3. Group interchangeability method (selective assembly)
This method is used mainly to obtain fits with small tolerances from parts whose mating elements are made to relatively large tolerances. To implement the method, increased tolerances are assigned to the dimensions that form the dimensional chain. Then, according to these tolerances, parts are manufactured, which are necessarily measured and distributed into separate groups according to actual dimensions. There can be several such groups, or several dozen, for example, in the bearing industry their number reaches 50. Assemblies are assembled using parts with the dimensions of one specific group.
The main advantage of the method is to obtain high precision connections using extended tolerances, i.e. manufacturing parts of lower precision. This allows for more economical production than if machining to tighter tolerances.
The disadvantages of group interchangeability include: the introduction of 100% measurement of parts; the need for additional production space and containers to accommodate groups of parts; tightening requirements for the accuracy of the shape of parts within the same size group.
5.4.4. Regulation method
This method is used at the design stage by changing (adjusting) one of the links, which is called compensation. The role of compensators is usually played by links, structurally made in the form of gaskets, stops, wedges, threaded pairs, etc. At the same time, the remaining links in the chain are processed to relatively large tolerances.
The advantage of the method is the ability to relatively easily ensure the accuracy of the closing link. Expansion links (most often spacers) are pre-fabricated in different sizes, and they are then easily selected during the assembly process.
The disadvantage of this method is the need for additional work to install, select or adjust compensators. In addition, if the expansion joints are made in the form of wedges or adjusting screws, then they themselves require additional fastenings, since during operation the expansion joints may become loose and dislodged.
5.4.5. Fitting and co-processing method
The fitting method is used mainly for single and small-scale production. For example, the beds of metal-cutting machines in the guides, before installing moving parts on them, are additionally processed (most often by scraping), and then the degree of adherence of the mating surfaces is checked “by paint”.
Plunger pairs for diesel fuel pumps must have a gap in the connection within the range of 0.4 - 2 microns. It is almost impossible to ensure such a small gap by simply selecting parts. Therefore, the parts of the plunger pairs are pre-selected so that they are partially connected, not even to their full length. After this, on special machines they are ground to each other using lapping pastes until mating is achieved along the entire length.
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Turning
Types of calibers and their scope
In mechanical engineering, the so-called alternative method of monitoring product shelf life is widely used. It allows you to divide products into good and defective. In this case, the actual values of the parameter being checked are not determined, but the fact of its compliance with the standard is established. When alternatively checking the geometric parameters of products, gauges are most often used.
Calibers are scaleless measuring instruments for checking linear dimensions, angles, shapes and relative positions of surfaces. There are several types of calibers.
Rice. 1. Smooth clamp gauge (a) and its tolerance range (b)
Smooth clamp gauges (Fig. 1) are used to control the lengths and diameters of the outer surfaces. They can be one-sided and two-sided, one-limit and two-limit. Single-determined staple gauges are made either passable or non-passable. To control the dimensions of the 8th accuracy class (and less accurate), clamp gauges with replaceable jaws are used. To control more precise products (up to 6th quality), the working surfaces of the gauges are equipped with a hard alloy. In small-scale and individual production, staple gauges are made from sheets, in large-scale and mass production - from forgings and castings.
Smooth plug gauges (Fig. 2) are used to control holes. Structurally, they are made in the form of a handle and a working part. The working part can be made integral with the handle or in the form of inserts and attachments. For plug gauges designed to control precise holes (6-12 grades), the inserts are made of hard alloy. Plug gauges can be single-sided or double-sided. One-sided ones are made passable or non-passable.
Smooth gauges allow you to control linear dimensions from 0.1 to 3150 mm. As the dimensions increase, the control error increases due to the increase in elastic deformations of the gauges.
For smooth plug gauges, the through side (PR) has the smallest limit size (i.e., it must pass into the hole), and the non-go through (NOT) side has the largest limit size (i.e., it must not pass into the hole). For smooth staple gauges, the through side (PR) has the largest maximum size, and the non-through side (NOT) has the smallest. According to their purpose, gauges are divided into working gauges (P), intended for checking parts by workers and quality control inspectors, receiving gauges (P), for checking parts by representatives of the customer, control gauges (K), for checking working and receiving gauges during the process of their manufacture and operation, and counter gauges ( K-I) - to control the wear of working calibers.
Rice. 2. Smooth plug gauge (a) and its tolerance range (b)
Rice. 3. Types of gauges: 1 - measuring plane, 2 - guide plane, 3 - product, 4 - marks
The gauges are marked with their type, the pass and fail sides, the controlled nominal size, the designation of the checked tolerance range, and the manufacturer's trademark.
Calibers for controlling dimensions in height and depth are varied both in design and principle of operation. The most commonly used calibers are those using the “light slit” method. The extreme sides of these calibers are designated by the letters B (large) and M (smaller).
Cone gauges are designed for testing smooth conical surfaces. Most often they control the conical shanks of tools (bushing gauges) and conical holes for their fastening (plug gauges). The limiting positions of the gauges relative to the controlled surface are determined by two marks marked on the gauge. Typically, such gauges are used in a set consisting of a plug gauge, a bushing gauge and a counter-plug gauge. The latter is designed to allow the bushing gauge to be fitted to the paint plug gauge.
Gauges for checking the shape and relative position of surfaces have a wide variety of designs. They can control the parallelism of planes, the alignment of holes, the symmetry of grooves, the parallelism of the plane and the axis of the hole, spline shafts and bushings, etc.
Thread gauges are used for comprehensive thread control. The external thread is controlled with a ring gauge, and the internal thread with a plug gauge. Thread gauges are manufactured and used in sets, which, in addition to the thread gauge, include control pass and no-go gauges. Along with unregulated calibers, adjustable ones are also used. The latter are adjusted using installation thread gauges, which in this case are also included in the kit.
Profile templates are flat gauges used to control the profile of shaped surfaces of a product. Control with such a template is carried out using the “light slit” method. The manufacturing accuracy of the profile template itself and its wear are checked using counter templates. The gauges are made from structural, tool and tool alloy steels. Equipping the working part of the caliber with hard alloy VK8 increases its durability several tens of times compared to calibers made of carbon tool steel.
The described tools do not make it possible to find out the real geometric parameter of the product. They are intended to determine whether or not a particular part has gone beyond the limits indicated for it by the working drawing (drawn up after the appropriate calculation has been carried out).
In other words, gauges set tolerances for the production of a product.
The calibration tool comes in the following types:
- "cork";
- "ring";
- bracket.
Calibers are usually divided into extreme and normal. The second ones listed contain the parameter that is required to be obtained on a specific part. Its suitability is determined by entering a caliber product with a certain level of density.
The limiting instrument has two parameters. One of them is equal to the maximum size of the product, the second - to the minimum. Such dimensions are called, respectively, pass-through and non-pass-through (one end of the tool must fit into the part being tested, but the other must not).
Limit calibers are used more often these days. And normal ones are usually used as controls. Note that it is easier to operate the maximum calibers. Working with normal tools requires a fairly high level of professionalism from a specialist, and their calculation is quite complicated.
The gauges that are necessary to control parts are called working gauges. And those tools that are used to control threads with gauges are counter-gauges (another name is control gauges). There are several GOSTs containing requirements for types of gauges, conditions of their production and wear rates.
2 Threaded gauges according to GOST 2016–86
This State Standard describes the technical requirements for the manufacture of thread gauges (TC) used to control cylindrical internal and external threads with a cross-section of 1–300 mm. In accordance with it, the main document for the release of a caliber is a drawing prepared by specialists and approved in accordance with the accepted procedure.
Types of calibers according to this GOST:
- “plug” and “ring” NOT (short profile) and PR (full profile);
- RK test plugs with full and shortened profile KNE-NE, KNE-PR, KI-NE, KPR-PR, KPR-NE (used to control threads with gauges, that is, they are counter-gauges).
Non-passable RCs are characterized by the following design features:
- “ring”: on such a caliber, a groove is necessarily carried out along the cylindrical outer surface; it is characterized by a smaller number of thread turns (if we compare them with this indicator for pass-through products);
- “plug”: there is no groove, the number of turns is also less than on standard feed-through gauges.
In addition, a no-go tool has two or one cylindrical belt (the so-called insert).
- according to GOST 801 – ШХ-15;
- according to Gosstandart 5950 – 9ХС and Х;
- according to Gosstandart 1435 - U12A and U10A.
Working surfaces of the RK types “plug” with a thread cross-section of 1–100 mm and “ring” with a cross-section of 6–100 mm, as well as the surfaces of nozzles and inserts used for metric threads, must be coated with a wear-resistant layer (usually chrome, which protects the product from ). It is allowed to produce control tools without special coating (without) when it comes to using them to check metric threads with interference.
GOST regulates the hardness of surfaces (working) of the Republic of Kazakhstan, according to the HRC scale it should be:
- “plug” with a cross-section of more than 3 mm and “ring” with a cross-section of more than 1 mm – from 59 to 65;
- “plug” with a cross-section of up to 3 mm and “ring” with a cross-section of up to 1 mm – 56 or more.
The hardness of calibers with a special layer varies from 57 to 65.
Tolerances and geometric parameters of working RCs are specified separately in the following GOSTs: 25096, 6357, 24834, 16093, 9562, 11709, 4608.
The roughness values in accordance with State Standard 2789 for control gauges should be no more than 0.2 microns, for workers - no more than 0.4 microns. And for the surface of the tool, the roughness is taken to be up to 0.8 microns (the internal section of the gauge is the “ring” type and the external section is the “plug” type).
3 Other requirements for the Republic of Kazakhstan according to GOST 2016
Tools of the "plug" type are produced with an internal and external center (caliber section less than 3 mm) and with an internal center (section more than 3 mm).
Elements of control devices with working surfaces must undergo an aging procedure.
On inserts of pass-through RK for metric threads with a pitch above 0.75 mm and a cross-section of more than 6 mm, a special mud groove is provided. It is laid before the first turn, and such a groove must cross subsequent turns parallel to the insert (its axis).
If the thread pitch of the RK “ring” does not exceed 1.5 mm, and that of the insert does not exceed 1 mm, the tool must have a chamfer. In those cases where rings and inserts have a larger pitch, GOST requires that the first turns on them be cut off and then blunted.
Any caliber must have the following information:
- designation of tolerance and the thread itself;
- manufacturer's trademark;
- appointment of the Republic of Kazakhstan;
- code "LH" when tools are manufactured with left-hand threads.
GOST 2016–86 allows not to indicate the accuracy class of the RK “ring” and “plug” for threads that comply with Gosstandart 6357 and a number of OST (in particular, 1262 and 1261).
Preservation of thread gauges (under standard conditions it is allowed for a period of 12 months) is carried out in accordance with GOST 9.014.
The described instruments are stored in a temperature range of 10–35 degrees Celsius in well-ventilated areas. There should be no alkali or acid vapors in the air. Transportation of the Republic of Kazakhstan is carried out in containers or in covered transport of any type.
4 Calculation of thread gauges and its features
The described threading tool is designed based on the following initial data:
- tolerance fields of the thread subjected to control;
- make-up length;
- external nominal cross-section.
All this information is available in the standard connection designation (nut as an internal thread plus a screw or bolt as an external thread).
The calculation of metric threads requires the establishment of the nominal internal and average cross-section of the connection. For trapezoidal threads (GOST 1981 24737), in addition to the average diameter, the following diameters are also set:
- nuts (internal and external);
- screw (internal).
The calculation itself, after determining all the above data, is schematically carried out as follows:
- the type of RC is selected (using a special plate);
- using formulas for trapezoidal and metric threads, all required diameters (middle, external, internal), as well as their permissible deviations, are calculated;
- the results established by the calculation are checked for the correctness of the performance parameters (for trapezoidal threads - according to Gosstandart 18466, for metric threads - according to Gosstandart 18465).
After this, select or calculate the thread length and make a drawing indicating the requirements for:
- type of heat treatment;
- the material used;
- location and shape of surfaces;
- accuracy of geometric parameters;
- roughness index.
It is necessary to make a drawing; without it, the calculation is considered incomplete.
Then it is necessary to clarify additional requirements for the symmetry of the steering wheels, their angles of inclination, the accuracy of steps and some other parameters. The specific design of the “plug” and “ring” shaped gauges is selected according to the type of threaded tool (the drawing, of course, reflects the chosen design). At this point the calculation is considered completed.
Currently, manual calculation of calibers is almost never done anywhere. Everything is done for a person by smart programs that are easy to find on the Internet on specialized sites. We will not provide links to such projects that help to carry out an accurate calculation of the RK, since you yourself can find them in a couple of clicks.
Calibers are scaleless measuring instruments designed to check the size, shape and relative position of the surfaces of parts. Calipers are classified as one-dimensional instruments, since the measuring parts of gauges do not change during the measurement process.
Calibers are divided into two groups: normal and extreme.
Normal calibers are manufactured according to the nominal size of the part being tested and have a measuring part equal to the average permissible size of the part being measured. A normal gauge should fit into a part with a greater or lesser density.
Limit calibers have dimensions nominally equal to the maximum dimensions of the part being measured. One of the sides of the caliber corresponds to the largest, and the other to the smallest specified limit size. When measuring with limit gauges, the pass side must fit into the hole or fit onto the shaft, and the second side - the non-go side - should not fit into the hole or fit onto the shaft. The non-pass side of the gauge differs from the pass side by an annular groove on the handle or by a shorter length of the measuring part. The non-go side of the gauge is shortened because it usually does not fit into the hole being tested. Using limit gauges, it is determined whether the actual dimensions of parts are outside the established limits or not.
Depending on the parts elements being checked calibers are divided as follows:
1) to check holes;
2) for checking shafts;
3) to check threads;
4) for checking conical holes, etc.
By purpose, calibers are divided into workers And reception rooms.
Working calibers used in the manufacture of products. They are used to check parts on the job site.
Receiver gauges are intended for inspectors who use them to check parts at control points or in technical control departments (QC).
In accordance with OST 1201, 1219 and 1220, calibers have the following designations:
R-PR (or PR) - the through side of the working caliber;
R-NOT (or NOT) - non-pass side of the working caliber;
P-PR - pass side of the receiving caliber;
P-NOT - non-pass side of the receiving gauge.
For calibers the following markings are applied:
a) the nominal size of the product for which the gauge is intended;
b) maximum deviations of the product (fit, accuracy class);
c) purpose of the caliber (PR - passing side and NOT - non-passing side);
d) trademark of the manufacturer.
On one-sided two-limit calibers, the designations PR and NOT are not placed.
There are many and varied designs of gauges for testing cylindrical surfaces (shaft and hole).
Rice. 58. Normal calibers:
a - plug gauge, b - ring, c - bracket
In Fig. 58 shows normal calibers: ring, plug and bracket.
Ring and staple check the diameter of the shaft, and cork- hole diameter. To measure shafts they are mainly used staples.
Rings allow you to more accurately check the shaft, since they cover its entire surface. However, the rings are expensive to manufacture and therefore their use is limited. In addition, rings cannot be used to measure journals in the middle of shafts, as well as shafts fixed in the centers. Of the staples, the most common are limiting one-sided staples (Fig. 59).
Rice. 59. Limit gauge-bracket
Adjustable brackets are the most convenient and widely used. They are manufactured with one fixed jaw and two inserts (PR - go-through and NOT - no-go). The inserts are set to a specific size within the regulation range from 3 to 8 mm. In the body 1 of this bracket there are two slots into which measuring inserts 2 are placed, secured with screws 3. When installing the bracket, the inserts are moved to the required size and fixed with set screws 4. Adjustable brackets have the advantage that in case of wear, the size of the bracket can be restored by moving the inserts . Adjustable clamps can measure shafts of different diameters (within the range of clamp adjustment).
Calibers, types and purpose. Control of macrogeometry parameters of parts using gauges
Calibers – measuring control tools designed to verify compliance of the actual dimensions, shape and location of the surfaces of parts with the specified requirements.
Gauges are used to control parts in mass and serial production. Calibers are normal and extreme.
Normal caliber– an unambiguous measure that reproduces the average value (the value of the middle of the tolerance field) of the controlled size. When using a normal gauge, the suitability of a part is judged, for example, by the gaps between the surfaces of the part and the gauge, or by the “density” of the resulting interface between the controlled part and the normal gauge. Gap assessment, therefore, control results largely depend on the qualifications of the inspector and are subjective.
Limit calibers– a measure or set of measures that ensures control of the geometric parameters of parts according to the highest and lowest limit values. Limit gauges are made to check the dimensions of smooth cylindrical and conical surfaces, the depth and height of ledges, and the parameters of threaded and splined surfaces of parts. Gauges are also made to control the location of surfaces of parts, standardized by positional tolerances, alignment tolerances, etc.
When testing by limit gauges, a part is considered suitable if the pass gauge passes under the influence of gravity, and the non-go gauge does not pass through the controlled element of the part. The control results are practically independent of the operator’s qualifications.
By design, calibers are divided into plugs and staples. To control holes, plug gauges are used, and to control shafts, clamp gauges are used.
By purpose, calibers are divided into workers and control .
Workers gauges are designed to control parts during their manufacturing and acceptance. Such calibers are used at enterprises by workers and inspectors of technical control departments (QCD). Tests gauges are used to control rigid working limit gauges or to adjust adjustable working gauges.
A set of working limit gauges for testing smooth cylindrical surfaces of parts includes:
· bore gauge (PR), the nominal size of which is equal to the largest maximum shaft size or the smallest maximum hole size;
· no-go gauge (NOT), the nominal size of which is equal to the smallest maximum shaft size or the largest maximum hole size.
The design of smooth gauges is based on the Taylor principle or the principle of similarity, according to which the passage gauges should be a prototype of the mating part and comprehensively control all types of errors of a given surface (checking the diameter and shape errors, including deviations from the straightness of the hole axis). This ensures the assembly of the connection. Non-go gauges must provide element-by-element control (control of the actual dimensions), therefore, the contact between the working surfaces of the gauges and the controlled surface must be point-like.
A working gauge that fully complies with the Taylor principle for checking a hole must have a pass-through side in the form of a cylinder with a length equal to the length of the mating or controlled surface (full plug), and a non-pass-through side in the form of an incomplete plug in the form of a rod with spherical tips. The working gauge for shaft control must have a pass side in the form of a ring with a length equal to the length of the mating or controlled surface, and a non-pass side in the form of a bracket with knife surfaces. In practice, due to the peculiarities of manufacturing and control technology, a violation of the Taylor principle is often observed; for example, gauges for testing small diameter holes are made in the form of full plugs, and for testing shafts - in the form of brackets.
Control of hole sizes is usually carried out with go-through and no-go plug gauges inserted into a common handle (Fig. 3.77 A).
Shaft gauges are usually made in the form of brackets with plane-parallel working surfaces (Fig. 3.77 b).
b | V |
Rice. 3.77. Sketches of calibers
If the go and no-go gauges for checking holes are made in the form of full plugs, then the no-go plug has a shorter length than the go-through one. For holes of large diameters, gauges with working surfaces in the form of an incomplete plug are more often used, for example, a sheet plug with cylindrical working surfaces, and the length of the working surfaces of a non-go-through plug is significantly less than that of a go-through plug. Each plug controls several cross sections of the hole (at least two mutually perpendicular sections are controlled).
When inspecting shafts with a clamp gauge, the surface is checked in several sections along the length and in at least two mutually perpendicular directions of each section.
If the parts are suitable, then, in accordance with the name, go-through gauges (PG) should pass through the controlled surfaces under the influence of their own weight, and non-go-through gauges (NOT) should not pass through.
When inspecting smooth gauges, a number of rules must be followed, in particular, use only gauges intended for this case (workers, as a rule, use new pass gauges, quality control workers can use partially worn gauges). It is necessary to ensure the cleanliness of the measuring surfaces, do not try to push pass and no-go gauges by force, and in order to avoid heating, do not hold the gauges in your hands for longer than is absolutely necessary.
The types of smooth non-adjustable gauges for monitoring cylindrical holes and shafts are established by GOST 24851-81, in which their various design types are assigned numbers (1...12) and corresponding names.
There are three versions of smooth calibers:
1. Single-limit plugs or staples (passing, marked PR, and non-passing - NOT), used primarily for the control of relatively large sizes.
2. Double-limit double-sided gauges, which speed up control somewhat. They are designed for relatively small sizes: staple gauges up to 10 mm and plug gauges up to 50 mm.
3. Single-sided double-limit gauges, which are more compact and almost double the speed of control. These gauges are available for a wide range of sizes.
Single-sided staples, starting with sizes over 200 mm for controlling shafts up to the 8th grade inclusive, must be equipped with heat-insulating handles.
Structurally smooth gauges can be made adjustable or non-adjustable.
Calibers for sizes over 500 mm, according to GOST 24852-81, are used only for testing parts of grades 9...17. These calibers have a single layout of tolerance fields.
Calculation of calibers comes down to determining the executive dimensions of measuring surfaces, limiting deviations in their shape and assigning optimal roughness. The starting point for deviations for passing smooth gauges is the passing limit of the shaft or hole, for non-passing gauges - their non-passing limit. For pass-through gauges, in addition to the manufacturing permit, a permissible wear limit is also provided separately.
For productive and accurate control of the internal dimensions of the control gauges during the process of finishing them during manufacturing and for quickly determining the moment of complete wear, smooth control gauges are used (Fig. 3.77 V).
The set of control gauges includes three gauges made in the form of washers
· control passage gauge (K-PR);
· control no-go gauge (K-NOT);
· gauge for monitoring the wear of the pass gauge (CI).
The control calibers K-PR and K-NE, due to the small tolerances of the working calibers for which they are intended to control, are made as normal, and not limiting calibers, and the suitability of the working calibers is determined using a subjective assessment of the compliance of the checked sizes with the control calibers.
The CI gauge is designed to control the permissible wear of the pass side and can be considered as a limit gauge that controls the limit of permissible wear.
Control gauges (for sizes up to 180 mm, blocks of gauge blocks can also be used) are designed to speed up checking the final dimensions of the pass and non-go sides when manufacturing non-adjustable or installing adjustable brackets (K-PR and K-NE), as well as to control the moment of complete wear of the pass-through staple gauges during their operation (CI).
Gauges for checking plug gauges are not manufactured. The dimensions of plug gauges are checked using universal measuring instruments, which is not difficult for external surfaces.
Manufacturing tolerances are established for all gauges, and for a pass gauge, which wears out more intensively when inspecting a part, a wear limit is additionally set.
Tolerances on the measuring surfaces of smooth gauges are established by GOST 24853-81 (for sizes up to 500 mm) and GOST 24852-81 (for sizes from 500 mm to 3150 mm). The tolerances of the working surfaces of the gauges are significantly less than the tolerances of the parts for which they are intended to control, and have been tested by many years of practice.
To construct diagrams of the location of tolerance fields, it is extremely important to determine the nominal dimensions of the gauges, which correspond to the maximum dimensions of the surface of the hole or shaft controlled by the gauge (Fig. 3.78).
The location of the caliber tolerance fields according to GOST 24853-81 depends on the nominal size of the part (the schemes differ for sizes up to 180 mm and over 180 mm and for qualifications 6, 7, 8 and from 9 to 17).
Rice. 3.78. To determine the nominal sizes of calibers
The standard establishes the following standards for calibers:
· N – approval for the manufacture of gauges for holes;
· N s – approval for the manufacture of gauges with spherical measuring surfaces (for holes);
· N 1 – approval for the manufacture of shaft gauges;
· N r – approval for the manufacture of a control gauge for the staple.
The wear of pass-through gauges is limited to the following values:
· Y – permissible deviation of the size of a worn-out pass-through gauge for a hole beyond the tolerance zone of the product;
· Y 1 – the permissible deviation of the size of a worn pass-through gauge for a shaft beyond the tolerance range of the product.
For all pass gauges, the tolerance fields are shifted inside the tolerance field of the part by the amount Z for plug gauges and size Z 1 for clamp gauges. This arrangement of the tolerance field of a pass-through gauge, subject to wear, makes it possible to increase its durability, although it increases the risk of rejection of suitable parts by a new gauge.
Executive It is customary to call the size of the caliber by which the caliber is made.
Posted on ref.rf
When determining the executive size of the caliber, the nominal size is replaced: the maximum limit of the caliber material with the location of the tolerance field “into the body” of the part is taken as the “new” nominal size. In the drawings of working plug gauges and control gauges, the largest size with a negative deviation equal to the width of the tolerance field is indicated; for staple gauges, the smallest size with a positive deviation.
Gauges are widely used for testing complex surfaces of parts, including spline and threaded surfaces. In this case, to design the working surfaces of calibers, the Taylor principle must be used.
For example, to control spline bushings, the working pass gauge is made in the form of a spline shaft, which allows you to simultaneously control the dimensions of the outer and inner diameters of the spline bushing, as well as the relative position of the outer and inner cylindrical surfaces of the bushing, the pitch and direction of the splines, and the width of the depressions. To control the no-go limits (limits for the minimum material of the part), a set of no-go gauges is used to check the actual dimensions of the spline bushing elements. The diameters are controlled by plugs, with an incomplete or full plug used for the internal diameter, and an incomplete plug used for the outer diameter of the spline bushing. The kit also includes a working gauge for checking the width of the slots.
To control the thread, use a working threaded plug with a full profile thread and a length equal to the length of the threaded mate. The set of no-go gauges includes a working no-go thread gauge with a shortened thread profile and reduced length of the threaded part, as well as smooth gauges for controlling the diameter of the protrusions. A no-go thread gauge should be screwed onto the mating piece by no more than one and a half turns.
Calibers, types and purpose. Control of macrogeometry parameters of parts using gauges - concept and types. Classification and features of the category "Gauges, types and purpose. Control of macrogeometry parameters of parts using gauges" 2017, 2018.