Vernier calipers are used to determine the outer and internal diameters, linear dimensions, depths of grooves and holes, as well as distances between ledges. Some modifications allow markings to be applied to the surfaces of workpieces. The tool is used to measure workpieces in mechanical and metalworking production areas, to control the production of wear surfaces when repairing equipment, and due to its ease of use, it is used in home workshops.
Shown in Fig. 1 caliper type ШЦ-1 consists of:
- Barbells.
- Framework.
- Measuring scale.
- Upper lips.
- Lower lips.
- Depth gauge.
- Vernier scales.
- Clamping screw.
The choice of caliper for a specific task is determined by the dimensions, design features of the part and requirements for dimensional accuracy. The tools differ in the following parameters:
- Measuring range. The length of the scale on the rod ranges from 125 to 4000 mm.
- Accuracy. Common modifications have an error of 0.1, 0.05, 0.02 and 0.01 mm.
- Functionality. There are calipers with and without a depth gauge.
- The number and shape of measuring surfaces. The jaws of single-ended and double-ended instruments are available in flat, pointed or rounded shapes.
- The design of the reading device. It can be vernier, mechanical, clock type or electronic.
Calipers are made from wear-resistant tool steels, and their measuring surfaces can be reinforced carbide tipped. To mark parts, cutters are installed on non-sharpened jaws (Fig. 2), complete with holders and clamping screws.
Measurement order
The tool and part need to be prepared for work: remove dirt, bring the jaws together and make sure that the readings correspond to “0”. To measure the outer diameter or linear dimension you must:
- spread the sponges by moving the frame;
- move until it fits snugly against the countersurfaces;
- fix the position of the frame with a locking screw;
- bring out a caliper to evaluate the results obtained.
To measure the internal size, the jaws are brought to “0” and then moved apart until they come into contact with the countersurfaces. If design features details allow you to see the scale, then the readings are read without fixation and removal.
To measure hole depth:
- by moving the frame, the depth gauge is extended;
- lower it into the hole to the bottom and press it against the wall;
- move the bar until it stops at the end;
- fix with a locking screw and remove.
The accuracy of the results depends on the correct positioning of the jaws relative to the part. For example, when determining the diameter of a cylinder, the rod must intersect or cross with its longitudinal axis at a right angle, and when measuring the length, it must be positioned parallel. In calipers of the ShTs-2 and ShTs-3 types there is an additional frame, which is movably connected to the main micrometric adjusting screw (Fig. 3). This design simplifies tool positioning. When taking measurements, the additional frame is fixed on the rod, and the position of the main frame is adjusted by rotating the micrometer screw.
Reading results
Vernier scale
The number of whole millimeters is counted from the zero division on the staff to the zero division of the vernier. If they do not match, then the size contains fractions of a millimeter corresponding to the accuracy of the tool. To determine them, you need to count on the vernier from zero to the line that coincides with the mark on the bar, and then multiply their number by the division value.
Figure 4 shows the dimensions: a – 0.4 mm, b – 6.9 mm, c – 34.3 mm. Vernier division value 0.1 mm
By hourly indicator
The number of whole millimeters is counted on the bar from zero to the last mark not hidden under the frame. Shares are determined by an indicator: the number of the division on which the arrow stops is multiplied by its price.
Figure 5 shows the size 30.25 mm. The indicator division value is 0.01 mm.
By digital display
To determine the internal size taken with a tool with radius measuring surfaces (lower jaws in Fig. 3), their thickness, which is indicated on the fixed jaw, is added to the readings on the scale. To count outer size, taken with a caliper with cutters (Fig. 2), their thickness is subtracted from the readings on the scale.
Marking
A regular caliper with pointed measuring surfaces copes with basic marking operations. By pressing one jaw against the side of the part, you can use the tip of the second to draw a line on the surface perpendicular to it. The line turns out to be equidistant from the end and copies its shape. To draw a hole, you need to mark its center: the recess serves to fix one of the jaws. Any technique of descriptive geometry can be used in a similar way.
Carbide tips and cutters leave noticeable scratches on parts made of steels with a hardness above 60 HRC. There are also narrow-profile calipers designed exclusively for marking.
Why do measurement errors occur?
The most common errors that reduce the accuracy of measurement results with a working instrument:
- Excessive pressure on the frame causes misalignment relative to the rod. The same effect is obtained if, when measuring with the lower jaws, the caliper is held by the upper jaws.
- Installation of jaws on fillets, chamfers and roundings.
- Distortions during positioning.
- Instrument calibration violation.
The first three mistakes most often arise from lack of experience, and go away with practice. The latter must be prevented at the stage of preparation for measurements. The easiest way is to set “0” on an electronic caliper: there is a button for this (in Fig. 6 the “ZERO” button). The hour indicator is reset by rotating the screw located at its bottom. To calibrate the vernier, loosen the screws securing it to the frame, move it to the desired position and fix it again.
Deformation of the caliper elements and wear of the measuring surfaces make the tool unsuitable for use. To reduce the number of defects in production, calipers undergo periodic verification by metrological services. To test the accuracy of the tool and acquire skills in living conditions You can measure parts whose dimensions are known in advance: for example, drill shanks or bearing rings.
- it's universal measuring device to determine the linear dimensions of parts with established accuracy. It can be used to measure external and internal dimensions parts, as well as the depth of the holes, subject to the presence of a retractable rod.
Design and use of calipers
The most popular areas of application for calipers are construction, repair of machinery and equipment, processing of metal and wooden products. The scope of application has virtually no restrictions - it can be used to determine dimensions with an accuracy of 0.1 or 0.05 mm (depending on the type of tool) in any field of activity - both in everyday life and in the aerospace industry. Application possibilities are limited only by the scale size and accuracy requirements (up to 0.01 mm for electronic calipers).
The design of a caliper is quite simple. The main element is a fixed rod with a scale and jaws for external and internal dimensions, to which movable and fixing elements are attached.
- Mobile frame;
- Movable jaws to determine the internal size;
- Movable jaws to determine the outer size;
- Vernier scale;
- Depth gauge rod;
- Screw for fastening the frame.
Some models may have a moving scale at the top with an inch measurement system.
How to take readings using a caliper
Before starting work, it is necessary to check the caliper for accuracy. To do this, you need to completely bring the jaws together and check that the zeros on both scales match. If there is no coincidence, then, depending on the required accuracy, it is necessary to either take another tool or take into account the existing error.
- For measurements external size spread the jaws of the caliper, place the object and connect them.
- Measuring the internal size is carried out by placing the corresponding upper jaws inside the measured area and moving them apart until they stop
- The jaws should rest against the edges of the part. If the surface is hard, then you can squeeze it a little for a tight fixation; for a soft one, this should not be done, as the result can be distorted.
- Check the position of the caliper relative to the part being measured for any distortions. To do this, the jaws must be located at the same distance from the edge of the part.
- Secure the vernier with the mounting screw.
- Determine the whole number of millimeters on the main scale.
- We find the coincidence of the stroke on the vernier with the zero of the main scale and count the number of divisions.
- We multiply the number of divisions of the vernier by the value of the division and sum it with the value of the main scale.
Types of calipers
In general, all types of calipers can be divided into mechanical and electronic depending on the type of scale. The main types, according to GOST 166-89, are:
- ШЦ-I - a tool with 2-sided placement of jaws for measuring external and internal quantities and a depth gauge.
- ШЦК - equipped with a circular scale for determining exact size. Easier to use than vernier calipers.
- ShTsT-I - one-sided jaws for measuring external linear dimensions. It is highly resistant to wear.
- ШЦ-II - equipped with two jaws for external and internal measurement and marking, as well as a micrometric feed frame.
- ШЦ-III - one-sided jaws for determining external and internal dimensions.
- ШЦЦ - electronic caliper with digital display.
Technical condition and verification of calipers
One of the most important requirements Ensuring the accuracy of a tool is its cleanliness. A magnetized layer of metal filings, preservative lubricant, dirt - all this can significantly distort the measurement result. The result is also affected by tool wear, deformation, and settings violations. To avoid this, annual verification of the caliper by a specialized specialist is necessary. service center with repairs and adjustments. The simplest check for the correctness of the readings is the coincidence of the zero strokes when the jaws are completely closed.
Current GOSTs
Production and testing of tools is regulated nearby state standards. Yes, it determines technical specifications on calipers GOST 166-89. The instrument verification procedure is defined in GOST 8.113-85.
TO category:
Helping a tool worker
Inspection and repair of vernier tools
Malfunctions of vernier tools and their inspection.
Most characteristic malfunctions Vernier instruments, as a result of which the accuracy of the readings is impaired, are: wear of the measuring surfaces and blunting of the sharp ends of the jaws; wear and deformation of the working surfaces of the rods and frame; skew of the main frame; incorrect installation of the vernier; weakening of the spring; wear of screw threads and micrometric feed nuts and a number of others. n The readings of caliper tools with a reading value of 0.05 mm are checked using gauge blocks of the 2nd accuracy class (6th grade), and with a reading value of 0.1 mm - with gauge blocks of the 3rd class.
The skew of the movable jaw, which is relatively motionless, is also detected using a gauge length.
Having installed the limit gauge in two extreme positions, take readings and, by their difference, judge the amount of non-parallelism of the measuring surfaces caused by the skew of the movable jaw.
The wear of the measuring surfaces is determined by the amount of mismatch between the zero strokes of the rod and vernier scales when the jaws are tightly moved. For vernier tools with a reading value of 0.02 and 0.05 mm, the clearance between the measuring surfaces should not exceed 0.003 mm, and for vernier tools with a reading value of 0.1 mm - 0.006 mm. In Fig. 79.6 shows how, using gauge blocks and a straight edge, you can determine by eye the amount of clearance between the measuring surfaces.
Rice. 1. Checking calipers.
A diagram for checking the wear of the working surfaces of the jaw for internal measurements is shown in Fig. 1, f. A gauge block is placed between the jaws for external measurements, and then using another caliper, the distance between the jaws for internal measurements is checked. This distance must be equal to the size of the gauge block.
The wear of the rod is determined using a measuring ruler against the light.
Repair of vernier tools. Wear on the working surfaces of rod tools is eliminated by straightening the jaws and then fine-tuning them. Straightening also eliminates defects in the measuring surfaces of the jaws and ensures that the zero strokes of the scales coincide. After straightening, they begin to fine-tune the measuring surfaces with plane-parallel laps, for which the caliper is secured in a vice, the lap is placed between the jaws, and the frame is moved until the jaws come into contact with the lap. In this position, the frame is secured with a locking screw and, moving between the jaws with a slight force, the surfaces are fine-tuned on the side of both sharp and blunt jaws until flatness, parallelism and same size solution of both sides.
Rice. 2. Finishing the measuring surfaces of the caliper.
The straightness of the measuring surfaces is checked with a straight edge, and the parallelism of the frame jaws to the rod jaws and the dimensions between them are controlled using end gauges, and the force with which the measure is inserted between the jaws must be the same for both sides. By inserting the end gauge not from the end of the jaws, but from the side along the entire plane and at the same time turning it slightly, you can determine the degree of parallelism of the surfaces. If the tile is held back by the ends of the jaws, rotating freely further over the entire surface, or has a gap in front, then the jaws are not parallel.
The outer surfaces of the blunt jaws are brought to parallelism. The size of the jaws should be equal to a whole number of millimeters with tenths (for example, 9.8 mm). After finishing the jaws, the vernier is set to the zero division of the rod. To do this, the jaws are moved until the measuring planes touch and the movable frame is clamped. Then the vernier is moved until the first and last divisions coincide, and its scales must exactly coincide with the first and corresponding divisions of the rod. The vernier is secured in this position.
During repairs large quantity With calipers, the fine-tuning of the measuring surfaces can be mechanized. The mechanized finishing scheme is shown in Fig. 2, b. The complex zigzag movement during mechanical finishing is formed as a result of two movements: horizontal reciprocating forward motion lap 1 (at i = 400 stroke/min and stroke length 23 mm) and vertical translational movement of caliper 2 (periodic feed movement 5 = 1.5-3 m/double stroke). To ensure finishing quality, both movements are coordinated with each other. The caliper only receives vertical movement when the lap moves. Halfway through the lapping stroke at maximum speed, the caliper is also provided with a small vertical feed. At the extreme points of the lap path, where its speed is zero, the vertical feed of the caliper stops. The finishing pressure should be P-2-3 kg/cm2.
When mechanically finishing the caliper jaws, cast iron laps are used, coated with M20 micropowder.
Repair of lightweight calipers when the jaws break is carried out in the following order. After vacation in salt bath cut off the worn or broken end of the sponge. Then in the thickened part of the leg disk cutter cut a groove equal in width to the thickness of the sponge. A new jaw blank is inserted into the groove of the leg and two or three holes are drilled together, then both parts are riveted. The sponges are filed to specified sizes and hardened. After cleaning, their measuring surfaces are fine-tuned.
Rice. 3. Repair of calipers.
If both jaws break, the upper leg is completely replaced with a new one. To do this, knock out the rivets and remove the broken leg from the rod. In the blank of the new leg, a rectangular window is milled and filed, the shape and size being equal to the end of the rod. Then a leg is put on the rod, the perpendicularity of its position relative to the edges of the rod is verified, holes are drilled in another place and the leg is riveted. The jaws are filed so that their configuration and dimensions match the shape of the frame jaws, and then they are finished.
Broken frame jaws are replaced with new ones, for which purpose, after knocking out the rivets and removing the unusable jaw, a blank of a new jaw is riveted in its place, filed down, hardened and finished.
Repairing broken jaws of calipers with a stamped rod is somewhat more difficult, since the entire rod, together with the jaws, has the same thickness and it is impossible to insert a new jaw. Riveting overlay does not always provide sufficient strength of the connection. Welding can be used, but it is best to replace the entire top of the rod with a new leg.
For this purpose, after annealing and cutting the jaws, the end of the ruler is milled or filed by hand so that shoulders are formed on the edges of the ruler, into which the leg rests. When filing the measuring planes of the leg jaws, it is necessary to ensure that the zero division of the vernier of the frame approximately coincides with the zero division of the scale on the ruler, since if the vernier is significantly displaced at its end, too much metal will have to be removed, which will worsen the quality of the repair.
Deformation of the rod can be caused by bending or uneven wear. work surface. Curvature of the rod is eliminated by straightening, carried out by bending it in a vice using three narrow brass spacers.
Uneven wear of the rod is eliminated by sawing and finishing on a lapping plate, checking the straightness with a straight edge or the paint method. Dents and nicks are cleaned with a velvet file, whetstone and fine sandpaper with oil.
To eliminate the misalignment of the vernier with the ruler scale, it is rearranged. If the end of the vernier rests against the wall of the frame window and cannot be moved, then it is filed down. At the same time, the holes for the screws are also sawed, after which, after rearranging the vernier, they secure it in the correct position.
Repair of other universal measuring instruments (protractors, height gauges and height gauges) is similar to the repair of calipers.
The main defects of the depth gauge can be non-straightness of the supporting surface, lack of perpendicularity of the ruler relative to the reference plane, and incorrect installation of the vernier.
To ensure the straightness of the supporting plane of the body and the end of the ruler, they are brought together on the plate. Having extended the ruler above the plane of the body, using a pattern square, check its perpendicularity relative to the reference plane.
Repair of a vernier is carried out in the same way as a vernier caliper. When setting the ruler to specific size its end is aligned with the plane of the depth gauge. In this position, the zero division of the vernier is combined with the zero division of the ruler scale or with the division corresponding to the height of the set of gauge blocks, after which the vernier is secured with screws.
Expanding the technical capabilities of the caliper.
Vernier calipers - universal tool, designed for high-precision measurements of external and internal dimensions, as well as hole depths.
I offer my homemade product that expands the capabilities of this wonderful tool, namely: drawing circles up to 28 centimeters in diameter. Agree, it’s very convenient to have two tools in one! Refinement will require a minimum of time and costs.
We will need: a circuit breaker, a pencil, a paper clip, a terminal block, a dowel, a pair of bolts.
To begin, we drill the caliper in three places: two holes on the rod and one on the vernier. The holes are 4 mm.
From the unnecessary circuit breaker remove the contact clip and the inner metal part from the terminal block.
We assemble our design: we attach the block to the rod, and the clamp with a pencil inserted into it on the vernier, we insert part of a paper clip to fix it.
The distance between the point of the dowel and the pencil lead was exactly one centimeter. In the future, we will add this centimeter to the radius of the desired circle that we want to draw. For example, we need to draw a circle with a radius of 10 cm. We set the caliper scale to 9 cm and mentally add another centimeter.
The main defects of a rod tool that can be eliminated during repair are errors in the divisions of the vernier, curvature of the guide rib of the rod, pitching and skew of the frame, non-parallelism of the measuring surfaces, their damage, wear of the base, etc.
Checking the correctness of the rod ribs and measuring planes of the jaws is carried out using blocks of gauge blocks, clamped between the measuring planes when moving the frame every 10 mm of the rod length. In any position of the frame on the rod, the force of pressure of the measuring planes on the block should be the same over the entire plane of the measure. If the contact of the measuring planes with any block is different for sharp and blunt jaws in different positions of the frame, this means that the rod is bent. If, at any position of the frame, the solution of sharp jaws is less than the solution of dull ones, or vice versa, then the caliper jaws are faulty.
To fix the rod, its working edge is checked for paint on a test plate, and the bulges are removed with a personal file or finishing. Then the second edge of the rod is made strictly parallel to the working edge, also using a file or finishing. After this, the measuring planes of the jaws are fine-tuned.
To fine-tune them, the caliper is secured in a vice with lead jaws (Fig. 177a). Finishing is carried out using a cast iron lap (Fig. 177, b). The lap is clamped between the jaws, for which the frame is brought close to the lap and the micrometric feed of the frame is fixed. The lap should move back and forth between the jaws without much effort.
Fig. 177.
Finishing the caliper jaws.
The distortion of the jaws is not difficult to establish. To do this, it is enough to clamp the block of gauge blocks between the jaws and if one of the sides of the block moves away from one of the sides of the jaws, then the misalignment is established. The misalignment of the working planes of the jaws in relation to the rod is corrected by grinding on a surface grinding machine. After grinding, both sharp and blunt jaws are polished with coarse GOI paste and polished with glass laps with a fine paste. The finishing of the jaws is considered complete if the lapping is carried out with the same force at both ends.
After finishing the jaws, check that the zero division of the rod coincides with the zero division of the vernier. To do this, the jaws move tightly and clamp the movable frame of the caliper. After making sure that there is no gap between the jaws, release the screws securing the frame to the vernier. Then move the frame with the vernier in one direction or another so that the first and last division of the vernier exactly coincides with the first and other corresponding division of the rod. Also pay attention to the fact that the second and third marks from the beginning of the vernier are located identically with the second and third marks from the end of the vernier in relation to the corresponding marks on the rod. After this, the screws are secured and, having once again checked the coincidence of the divisions, the installation of the vernier is considered complete. If, when installing the vernier, it is not possible to move it due to the gap in the holes for the screws, the holes are expanded using a needle file.
Breakage of the caliper jaws very often occurs. When correcting this defect, one of three decisions is made, shown in Fig. 178: shorten the length of the jaws (Fig. 178, a), remove one pair of jaws (Fig. 178.6) or make a cutout to insert a new jaw (Fig. 178, c). Sometimes a new one is welded in place of a broken jaw.
Fig. 178.
Repair and restoration of caliper jaws.
Correction of defects in lightweight calipers is carried out mainly by straightening with subsequent fine-tuning of the measuring planes. So, if, even when the working surfaces of the jaws are worn out, the zero stroke of the vernier does not coincide with the zero stroke of the rod, then after fine-tuning the measuring planes this error will be even greater.
Therefore, it is corrected by straightening. The stationary sponge is placed on a hardened block secured in a vice, and it is struck at place a (Fig. 179) so that its nose moves down. Impacts are made on both sides of the caliper. The same is done with the sponge of the movable frame, hitting it in place b. The sharp ends of the jaws are straightened in places a and b.
Fig. 179.
Repair of a lightweight caliper (arrows show the locations of impacts during straightening).
After straightening, the measuring planes are cut down and adjusted until the divisions of the rod and the vernier coincide, and finally the nicks are cleaned and all planes are polished with fine sandpaper.
Correction of the gage base is carried out by lapping on a lapping plate using grinding powders.