The outer measuring claws of the vernier caliper are mostly knife-edge measuring surfaces, and the flatness and parallelism of the measuring claws are not easy to meet the requirements when grinding and repairing, and there are often gaps at the knife edge when the two measuring surfaces are closed after grinding. In order to prevent gaps, sometimes only a small grinder can be used to grind only the wide surface portion. As a result, the wide surface is concave after grinding, and the transition between the wide surface and the knife edge is slightly convex. When the two measurement surfaces are closed, only the transitional surface contacts. , The flatness and parallelism are still not easy to pass, for which it has to be polished two or more times.
The above problems are mainly caused by improper selection of the force point when grinding. To correctly select the position of the force point, the caliper structure needs to be analyzed. The vernier caliper is composed of a main ruler, a vernier frame, a spring sheet, etc. The main ruler and the cursor frame have a reference surface respectively. Before measuring the measurement surface of the claw, the straightness of the main ruler and the reference surface of the vernier frame should be repaired firstly. After the restoration is qualified, the spring sheet is installed, and the outer measuring surface can be ground after eliminating the gap between the main ruler and the cursor frame. The two reference planes of the main ruler and the cursor frame are closely attached by the elastic force of the spring piece installed in the cursor frame, so as to ensure the correct position and relationship between the main ruler and the cursor frame. When grinding the measuring surface, if the position of the force point is not properly selected, this positional relationship will be destroyed. Grinding force point is usually in the middle of the vernier measurement claw above the direction of force, vertical downward, as shown in Figure 1. This creates two problems: (1) Since the area of ​​the knife edge of the outer measuring jaw is small, the smaller the area under the same pressure, the greater the pressure, which results in a corresponding increase in the amount of grinding and therefore two measuring jaws. Gaps appear at the edge of the knife when closed; (2) Since the two reference surfaces of the main ruler and the cursor frame are in elastic contact with the spring pieces, the grinding force under the action of the grinder may damage the close fitting state of the two reference surfaces and make the cursor The frame is deflected by a slight angle from top to bottom (as shown in Fig. 2), so that the amount of grinding at the edge of the knife edge increases correspondingly, creating a clearance at the edge of the knife when the two measuring surfaces are closed.
figure 1
figure 2
Practical experience shows that in order to prevent the occurrence of gaps, the point of grinding force should be selected outside the vernier box to measure the root of the claw, and the direction of force application is inclined by 45°, as shown in FIG. 3 . The grinding force of 45° is decomposed into the horizontal component force and the vertical component force, wherein the horizontal component force makes the reference surface of the cursor frame fit closely with the reference surface of the main ruler so as to ensure the correct position cooperation relationship between the cursor frame and the main ruler; Force the two measuring surfaces and the grinder into close contact and provide the grinding pressure so that the flatness and parallelism of the two measuring surfaces after grinding can be ensured.
image 3
With this grinding method, only one grinder is required to grind the flatness and parallelism of the knife-shaped outer measuring jaws without using a small grinder for two grindings.