# A complete list of how to use Every measuring tools

## A. Steel ruler

Steel ruler is the simplest length measuring tool, it has four specifications of 150, 300, 500 and 1000 mm. The following picture is the common 150 mm steel ruler.

A steel ruler is used to measure the length of a part, but its results are not very accurate. This is due to the inscribed spacing of the steel ruler for 1 mm, and the width of the inscribed line itself is 0.1 to 0.2 mm, so the measurement of the reading error is relatively large, can only read the number of millimeters, that is, its minimum reading value of 1 mm, than 1 mm small value, can only be estimated and obtained.

If the steel straightedge directly to measure the diameter of the part size (shaft diameter or hole diameter), the measurement accuracy is worse. The reason is: in addition to the steel ruler itself, the reading error is relatively large, but also because the steel ruler can not be placed exactly in the correct position of the diameter of the part. Therefore, the measurement of the diameter of the part size, you can also use the steel ruler and inside and outside the calipers together.
Second, inside and outside calipers
The following figure shows the two common internal and external calipers. Inner and outer calipers are the simplest comparative gauges. The outer caliper is used to measure the outer diameter and flat surface, and the inner caliper is used to measure the inner diameter and notch. They can not directly read out the measurement results, but take the measured length dimension (diameter also belongs to the length dimension), read it on the steel ruler, or take the required dimension on the steel ruler first, and then check whether the diameter of the part matches.

First of all, check the shape of the jaws, the shape of the jaws has a great impact on the accuracy of measurement, should pay attention to the shape of the jaws often trimmed, the following figure shows the caliper, the shape of the jaws good and bad comparison.

When adjusting the opening of the caliper, you should gently tap both sides of the face of the caliper foot. First use both hands to adjust the caliper to an opening similar to the size of the workpiece, then tap the outside of the caliper to reduce the opening of the caliper and tap the inside of the caliper to increase the opening of the caliper. As shown in Figure 1 below. However, the jaws should not be tapped directly, as shown in Figure 2 below. This will cause measurement errors due to the damage of the jaws of the caliper to the measurement surface. You should not tap the caliper on the guide rail of the machine. This is shown in the picture below.

## 2. the use of external calipers

When the outer caliper takes the size on the steel ruler, as the following figure, the measuring surface of one pincer foot is against the end of the steel ruler, and the measuring surface of the other pincer foot is aligned with the middle of the required size inscription, and the joint line of the two measuring surfaces should be parallel to the steel ruler, and the human line of sight should be perpendicular to the steel ruler.
With a good size in the steel ruler outside the caliper to measure the outside diameter, to make the two measuring surface of the line perpendicular to the axis of the part, by the weight of the outer caliper slide over the outer circle of the part, we should feel in the hands of the outer caliper and the outer circle of the part is exactly point contact, at this time, the distance between the two measuring surface of the outer caliper, is the outside diameter of the measured parts. So, using the external caliper to measure the outside diameter, is to compare the external caliper and the outer circle of the part contact tightness, the following chart to the caliper’s self-weight can just slide down as appropriate. If when the caliper slides over the outer circle, we have no contact feeling in our hands, it means that the outer caliper is larger than the outer diameter size of the part, such as by the weight of the outer caliper can not slide over the outer circle of the part, it means that the outer caliper is smaller than the outer diameter size of the part. Do not put the caliper skewed on the workpiece measurement, so there are errors. Because the caliper has elasticity, the outer caliper force pressed through the outer circle is wrong, not to mention the caliper horizontal card up. For the large size of the outer caliper, by its own weight to slide over the outer circle of the part has been too much pressure to measure, at this time should hold the caliper for measurement.

## 3. The use of the inner caliper

When using the inner caliper to measure the inner diameter, should make the two jaws of the measuring surface of the joint line exactly perpendicular intersect the axis of the inner hole, that is, the two measuring surfaces of the jaws should be the two end points of the diameter of the inner hole. Therefore, the measuring surface of the lower jaw foot should be stopped on the bore wall as a pivot point when measuring.

The upper clamp foot from the hole slightly to the inside some gradually try outward, and swing along the circumference of the hole wall, when the distance along the circumference of the hole wall can swing for the smallest, it means that the two measuring surfaces of the inner clamp foot have been in the two endpoints of the diameter of the inner hole. Then the caliper from outside to inside slowly move, can test the roundness tolerance of the hole.

## Use the steel straightedge or the outer caliper to measure the inside diameter.

It is to compare the tightness of the inner caliper in the hole of the part. If the caliper in the hole has a large free swing, it means that the caliper size is smaller than the aperture; such as the caliper can not be put into, or put into the hole after the tight can not swing freely, it means that the size of the caliper than the aperture, such as the caliper into the hole, according to the above measurement method can have 1 ~ 2mm free swing distance, then the aperture and the caliper size is exactly equal. Do not grab the caliper by hand when measuring.

So that the hand feeling is gone, it is difficult to compare the tightness of the inner caliper in the hole of the part, and make the caliper deformation and measurement error.

## 4. the scope of application of the caliper

Caliper is a simple gauge, because it has a simple structure, easy to manufacture, inexpensive, easy to maintain and use, widely used in the measurement and inspection of the size of parts with low requirements, especially for the measurement and inspection of forging and casting blank size, caliper is the most suitable measuring tool. Although calipers are simple gauges, as long as we master well, can also obtain a high degree of measurement accuracy. For example, when comparing the diameter of two shafts with external calipers, the difference between the shaft diameter is only 0.01mm, experienced teachers can also distinguish. Another example is the use of internal calipers and the outside diameter of the percentage of the joint measurement of the size of the bore, experienced teachers have full confidence in this method of measuring the bore with high precision. This inside diameter measurement method, called “inside the caliper to take a percentage”, is the use of the inside caliper in the outside diameter of the percentage to read the exact size.

Then go to measure the internal diameter of the parts; or the card in the hole to adjust the contact with the hole tightness, and then read out the specific size on the outside diameter scale. This measurement method, not only in the lack of precision inside diameter gauges, is a good way to measure the inside diameter, but also, for a part of the inside diameter, because it has a shaft in the hole and the use of precision inside diameter gauges have difficulties, then the application of the inside caliper hitching OD percentage measuring inside diameter method, it can solve the problem.
Third, the plug ruler
Plug ruler is also known as the thickness of thin gauge or gap piece. Mainly used to test the machine tool special fastening surface and fastening surface, piston and cylinder, piston ring groove and piston ring, crosshead slide and guide plate, into the exhaust valve top and rocker arm, gear meshing gap between the two combined surface clearance size. The stopper is made up of many layers of thin steel sheets of varying thickness.

According to the group of plug ruler made a plug ruler, each piece in each plug ruler has two parallel measuring planes, and all have thickness markings for combination use. When measuring, according to the size of the bonding surface gap, use one or several pieces overlapping together to plug into the gap. For example, with 0.03mm .03 to 0.04mm between, so the plug ruler is also a boundary limit gauge. The specifications of the stopper gauge are shown in the table.

Is the host and shaft system flange positioning inspection, the straightedge attached m plug ruler in the shaft system thrust axis or the first intermediate axis as the reference of the flange outer circle of the prime line, with the plug ruler to measure the straightedge and its connection to the diesel engine crankshaft or reducer output shaft flange clearance ZX , ZS, and in turn in the flange outer circle of the upper, lower, left, right four positions. The following picture is to check the clearance of the tightening surface of the tailstock of the machine tool (<0.04m).

The following points must be noted when using the stopper.

1. according to the clearance of the bonding surface to choose the number of pieces of the plug gauge, but the fewer pieces the better.
2. not too much force when measuring, so as not to bend and break the ruler.
3. can not measure the workpiece with high temperature.

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