TO category:
Helping a tool worker
Inspection and repair of vernier tools
Malfunctions of vernier tools and their inspection.
The most typical malfunctions of caliper tools, as a result of which the accuracy of 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 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.
Rod wear is set straight edge to 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 they touch measuring planes and clamp the movable frame. 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.
When repairing a large number of calipers, the finishing 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 the result of two movements: the horizontal reciprocating movement of the lap 1 (at i = 400 dv./min and a stroke length of 23 mm) and the vertical translational movement of the caliper 2 (periodic feed movement 5 = 1, 5-3 m/double lap stroke). To ensure finishing quality, both movements are coordinated with each other. The caliper only receives vertical movement when the lap moves. At half 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, a groove is cut with a disk cutter, the width being equal 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 they put a leg on the rod, check the perpendicularity of its position relative to the edges of the rod, drill holes in another place and rivet the leg. 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 fix it in correct position.
Repair of other universal measuring instruments(protractor gauges, height gauges and vernier depth 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 a certain 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.
In addition to various measuring instruments, a home workshop should also have a caliper, which is often needed where a tape measure or ruler is not suitable.
Below we will look at what such a measuring instrument is, what types are found and how to use it correctly in order to obtain the most accurate measurement data.
Purpose of a caliper
This measuring tool is used mainly to obtain the most accurate data when determining the outer and inner diameters of pipes, their wall thickness, to calculate the center distance in holes, the dimensions of cylindrical parts, wire thickness and metal sheet, as well as other materials of small dimensions and small products.
With such a device it is convenient to measure the depth of grooves, holes and grooves, various recesses with great accuracy in the most hard to reach places. The accuracy of a caliper in measurements reaches tenths and hundredths of a millimeter, which cannot be achieved by such a simple tool as a ruler or tape measure.
The tool, according to GOST 166-89, is made of stainless or carbon steel coated with a chrome-plated composition. Comprises:
- a rigid metal ruler called a rod (hence the name of the tool - caliper);
- measuring protrusions - jaws;
- an auxiliary frame with a vernier scale, otherwise called a vernier, which allows measurements to be made with an accuracy of tenths and hundredths of a millimeter, depending on the type of instrument;
- movable ruler of the depth gauge, rigidly connected to the jaws.
The vernier caliper scale can have different lengths and number of divisions. 10 divisions on the vernier scale make it possible to measure with an accuracy of up to 0.1 mm, 20 divisions provide a measurement accuracy of up to 0.05 mm:
Sponges can be upper and lower. On the surface of the lower - indicated minimum size measured parts. The ends of the lower jaws are made in the form of rectangles. The upper ones are pointed and beveled vertically, which allows them to mark on any materials and parts, without the use of other marking devices (i.e., directly with the sponges, you can draw a line exactly in size due to the sharp ends).
Using the upper jaws, the internal dimensions of holes, pipe diameters, grooves, and various recesses are measured. To measure external parameters, lower jaws are used. To measure length deep holes a depth gauge ruler is used, which extends from the main rod:
To fix the movable frame with a vernier scale on the ruler, there is a special fastening screw. Some caliper models are equipped with a scale round shape and a movable frame, the scale of which is designed to take measurements in inches. At the same time, the vernier scale of such a device allows measurements with an accuracy of up to 0.128 inches.
Types of calipers and technical characteristics
The classification of such measuring instruments is carried out according to several parameters - the method of taking readings, the type of scale, the location of the jaws. All these differences are reflected in the markings of the device.
U different types The following types of scales can be used for taking measurement readings:
- vernier scale;
- scale located on the dial;
- using a scoreboard with a digital indicator.
According to their design, calipers are divided into the following types:
- Single-sided tools made of carbide steel and marked ШЦТ.
- Mechanical models with one- or two-sided arrangement of jaws, marked as ШЦ-I, ШЦ-II, ШЦ-III, measurements on which can be taken using a vernier scale.
- A device equipped with a circular scale is marked ShIK or ShTsK and allows for more accurate measurements than devices with a vernier scale. The dial scale shows fractional readings, while the bar itself shows whole numbers.
- Latest generation electronic caliper with digital display showing the distance between internal surfaces sponges, is marked Shtsts and can work in symbiosis with a PC. This is the best device that allows you to quickly, without unnecessary calculations, see measurement data that is carried out with high accuracy up to 0.01 mm.
The ShTs-II tool differs from the ShTs-I model in that it has an additional frame equipped with a locking screw and connected to the main frame. A fixed additional frame allows you to bring the ends of the jaws in for more accurate measurement of the internal dimensions of the holes.
The ShTs-III device differs from the ShTs-II model in that it does not have one pair of upper marking jaws. Used for measuring large parts.
How to use a caliper correctly
Before using the tool, you must check it for serviceability and accuracy. To do this, you need to inspect it and remove any existing dirt from all parts. It is also necessary to check whether the zero marks on the main scale and the vernier scale coincide when the lower jaws are tightly connected.
It is best to fix the part being measured in a stationary state, but you can also hold it in your left hand, the main thing is to prevent it from moving during the measurement process. If you need to measure the external dimensions of any part, you need to spread the jaws and tightly cover the object being measured with them. In this case, the part must be in the correct position, without distortion and should not move. The next step is to fix the part in the caliper by screwing in the mounting screw, without excessive force. Only after this can you start reading the readings.
When using the ShTsTs device, you do not need to calculate the dimensions of the part being measured; all this is shown on the display. It is also not difficult to take measurements when working with the ShCK device. Integer numbers on the bar are indicated by the edge of the movable frame; hundredths or tenths of a millimeter are indicated by a dial scale.
But with a mechanical instrument ШЦ-I, ШЦ-II and ШЦ-III it will be necessary to compare the values of the main scale and the vernier scale. First, the size is determined in whole numbers, i.e., the reading on the main scale, which is determined by the position of the first mark of the vernier scale. Then, depending on the type of caliper, the size is determined in tenths or hundredths of a millimeter.
Total, Measurement algorithm:
- We look at the top scale to see how many whole millimeters fit.
- On the lower scale we look at which division coincides most closely with the division on the upper scale (as if it turns into one line) - these are tenths and hundredths of a millimeter.
Let's look at the picture to see how the measurement of 28.55 millimeters is obtained:
When using a tool, you should take into account the error of the caliper, which may arise due to improper storage, mechanical damage, contamination of the tool, and the temperature state of the part being measured. Optimal temperature For measurements this device has a range of 10–40 degrees above zero. To obtain the most reliable measurement data when using a caliper, it is recommended to take several measurements and calculate the arithmetic average. Upon completion of measurements, the device must be wiped dry and stored in a case.
This is where the article ends. Today we learned what a caliper is, what types it comes in and how to take measurements with it.
Expanding the technical capabilities of the caliper.
Vernier calipers are a 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: circuit breaker, pencil, paper clip, terminal block, dowel, 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 caliper got its name due to the main element of its body - the rod, but the compass we are used to is a little far from this tool in its structure. We will try to understand a subject full of mysteries with the help of this article, we will look at its structure and operating principle.
Vernier caliper design - main components and their purpose
The design of a caliper does not seem complicated from the outside, but its parts are so compact and optimally arranged that they make this device simple and easy to use. And it can do a lot, and the measurements that are performed with its help are very important in many areas of industry and construction. When using a caliper, we obtain the linear dimensions of objects, both external and internal. And the accuracy, which in some models reaches an enviable level, makes this simple tool increasingly in demand.
The purpose of a caliper is to measure lengths, diameters, depths, but let’s look at what provides this capability using the example of the simple type this device. The main unit is a ruler, which is called a rod, giving part of the name to the tool. The divisions on it are usually 1 mm, and the total length is usually 15 cm, but individual models may be longer. The ruler determines the maximum size that this tool can measure.. Which means maximum length or the diameter of the object should be no more than 15 cm.
At the end of the ruler there are sponges, or rather their halves, and the other halves are located on a movable frame, which moves along the ruler, measuring the size of the object being examined. There are internal and external sponges; in the former, the incisors face outward, in the latter, they face each other. Consequently, the first ones are inserted into the object and moved apart to fix the internal geometric parameter, and the second ones are moved apart widely and then come closer to fix the object under study among themselves. To accurately take the size or transfer it to another surface, the movable frame can be fixed with a special screw, which is located on it.
On the main ruler we can look at the integer value of the desired size, but the vernier scale, which is applied to the bottom of the frame so that it is exactly under the main marking of the ruler, will help to clarify the result. The vernier has ten divisions, each of which measures 1.9 mm, the entire scale is 1.9 cm long. These are the parameters of a regular household caliper; on other models this ratio changes. Having found a division of the vernier that coincides with any division of the main scale, you can refine the desired value to tenths of a millimeter. The use of a caliper is not limited to the internal and external dimensions; you can also mark the depth of the holes; for this there is a tail that extends from the ruler. This is a depth gauge scale.
Vernier calipers - classification and marking
The measuring instrument, a caliper, can be of 3 types and about 8 standard sizes, at least according to domestic standards regulatory documents. Moreover, when purchasing any precision instrument, it is important to focus on the standards by which it is manufactured and calibrated. It is divided into types depending on the indicator of the measured value from which we take the required numbers. This there can be vernier (ShTs), dial (ShTsK) and digital (ShTsTs) calipers. In the first case, we will have to run our eyes over both scales, count the divisions and report the result. In the second case, we will see numbers on a mechanical scale with a moving arrow, but in the third case, we will be shown the finished result on the display.
Within these types, further subspecies can be divided depending on the design and length of the main line. For example, you can divide tools by the type of material from which they are made. An example of a hard alloy tool is ShTsT-I. There are differences in the structure of the sponges or additional accessories. Thus, ShTs-I and ShTs-III differ in the location of the jaws; in the first case it is bilateral, and in the second it is unilateral. But the ShTs-II has a micrometric feed frame, which will make marking easier if you need to transfer your measurements to another plane. There is no point in discussing the differences in standard sizes for a long time; one has only to say that the larger the ruler, the greater the error in the obtained values.
How to measure with a caliper - instructions for beginners
Most technically advanced people intuitively understand how to use a caliper, so we will briefly recall the main points.
How to measure with a caliper - step-by-step diagram
Step 1: Securing the Part
First check the tool for serviceability, to do this, reduce the jaws without the part to zero, look at the clearance, how correctly they are connected, and also look at the scale to see if the zeros on the two scales match. After a positive result, you can begin working with the part. It is most convenient to work in cases where the tool is in your right hand, and the part being measured is in your left, or is completely fixed somewhere. If you are left-handed, then the relationship is, of course, reversed. For measuring external size spread the jaws of the caliper, place an object between them and connect them. They should rest against the edges of the part being examined. If it is hard, you can lightly squeeze the lips for a firm touch. If the part is soft, do not do this, the results will be distorted.
The force is controlled simply; if you try to move the jaws relative to the object, then they should do it reluctantly, but if you also need force for this, then you have clearly squeezed.
It is more convenient to move the frame thumb right hand, holding the barbell with the rest. Check the position of the caliper relative to the object, whether there are any distortions (the jaws should be at the same distance from the edge of the object on both sides), it is better to raise the structure to eye level. To see more clearly, it is better to hold the object with your left hand in the plane behind the instrument, and not in front. Now you should carefully tighten the fastening screw with your index finger and thumb, while the rest should continue to hold the bar. When the value is fixed, the part can be put aside and proceed to study the next stage, how to measure the resulting number with a caliper.
Step 2: Remove the value
It is best to read readings at eye level. First of all, we write down the value of the main scale, i.e. integer. To do this, we look for the stroke on the main rod that is closest to the zero value of the vernier, this is an integer number of millimeters. You can remember it, or you can mark it somewhere on your draft. Now we are looking for a line on the vernier that is closest to its zero, but also exactly coincides with some division on the rod. Its serial number should be multiplied by the division value of the vernier used (usually 0.1 mm). If you are not sure that you know this value, look in the passport of this caliper.
Now it's a small matter, you just need to sum up these numbers, and the result is ready. For example, you had a value of 35 mm on the bar, and 4 more divisions were counted on the vernier, then general meaning equals 35.4 mm (3.54 cm). After work, the instrument is wiped (degreased), the jaws are slightly moved apart (by a couple of mm), the clamp is loosened and placed in the case. If you plan to store it for a long time, you can lubricate it against corrosion.
Determination of readings by vernier
To determine the readings of a caliper, it is necessary to add the values of its main and auxiliary scales.
- The number of whole millimeters is counted on the bar scale from left to right. The pointer is the zero stroke of the vernier.
- To count fractions of a millimeter, it is necessary to find the vernier stroke that most accurately matches one of the strokes of the main scale. After this, you need to multiply the serial number of the found vernier stroke (not counting zero) by the value of its scale division.
Measurement result equal to the sum two quantities: the number of whole millimeters and fractions of mm. If the zero line of the vernier exactly coincides with one of the lines of the main scale, the resulting size is expressed as an integer.
The figure above shows the readings of the ShTs-1 caliper. In the first case they are: 3 + 0.3 = 3.3 mm, and in the second - 36 + 0.8 = 36.8 mm.
The instrument scale with a division value of 0.05 mm is presented below. For example, two different indications are given. The first is 6 mm + 0.45 mm = 6.45 mm, the second is 1 mm + 0.65 mm = 1.65 mm.
Similar to the first example, you need to find the strokes of the vernier and the rod that exactly match each other. In the figure they are highlighted in green and black, respectively.
Mechanical caliper device
The design of a double-sided caliper with a depth gauge is shown in the figure. The measurement range of this tool is 0-150 mm. It can be used to measure both external and inner dimensions, hole depth accurate to 0.05 mm.
Essential elements
- Barbell.
- Frame.
- Sponges for external measurements.
- Sponges for internal measurements.
- Depth gauge ruler.
- Locking screw for fixing the frame.
- Vernier scale. Serves to count fractions of millimeters.
- Bar scale.
The jaws for internal measurements 4 are knife-shaped. Thanks to this, the hole size is determined on a scale without additional calculations. If the caliper jaws are stepped, as in the ShTs-2 device, then when measuring grooves and holes, their total thickness must be added to the readings obtained.
Vernier reading value y various models tool may vary. So, for example, for ShTs-1 it is 0.1 mm, for ShTs-II it is 0.05 or 0.1 mm, and the accuracy of devices with a vernier reading value of 0.02 mm approaches the accuracy of micrometers. Design differences in the design of calipers can be expressed in the shape of a moving frame, measurement ranges, for example: 0–125 mm, 0–500 mm, 500–1600 mm, 800–2000 mm, etc. The measurement accuracy depends on various factors: vernier reading values, work skills, good condition of the tool.
The procedure for carrying out measurements, checking serviceability
Before work, check the technical condition of the caliper and, if necessary, adjust it. If the device has warped jaws, it cannot be used. Nicks, corrosion and scratches on working surfaces are also not allowed. It is necessary that the ends of the rod and the depth gauge ruler coincide when the jaws are aligned. The instrument scale must be clean and easily readable.
Measurement
- The caliper jaws are pressed tightly against the part with little force, without gaps or distortions.
- When determining the outer diameter of a cylinder (shaft, bolt, etc.), make sure that the plane of the frame is perpendicular to its axis.
- When measuring cylindrical holes, the jaws of the caliper are placed at diametrically opposite points, which can be found by focusing on the maximum scale readings. In this case, the plane of the frame must pass through the axis of the hole, i.e. Measurement along the chord or at an angle to the axis is not allowed.
- To measure the depth of a hole, a rod is placed at its edge perpendicular to the surface of the part. The depth gauge ruler is pushed all the way to the bottom using a movable frame.
- The resulting size is fixed with a locking screw and the readings are determined.
When working with a caliper, monitor the smooth movement of the frame. It should sit tightly on the bar without swaying, while moving without jerking with moderate force, which is regulated by the locking screw. It is necessary that when the jaws are aligned, the zero stroke of the vernier coincides with the zero stroke of the rod. Otherwise, reinstallation of the vernier is required, for which the screws securing it to the frame are loosened, the strokes are aligned and the screws are re-fastened.
