Method for generating and eliminating medium diameter error during tap grinding (2)

1) The influence of the straightness of the longitudinal guide rail in the vertical plane on the diameter of the tap diameter can be seen from Figure 1. Due to the straightness error of the guide rail in the vertical plane, the center of the tap is lower than the center of the grinding wheel. The increment ∆r can be calculated by:

2=(R+r+∆r)2-(R+r)2≈2(R+r)∆r

∴∆r= ∆2

2(R+r)

Set the grinding wheel radius R=200mm, the center of the tap is lower than the center of the grinding wheel=0.05mm, the tap radius is r=10mm

Then: ∆r = 0.052 = 0.000 005 9mm

2 (200+10)

It can be seen that the straightness of the guide rail in the vertical plane has little influence on the precision of the tap diameter.

2) The influence of the straightness of the longitudinal guide rail in the horizontal plane on the precision of the tap processing This error has a direct influence on the precision of the tap processing. If the middle of the V-shaped guide rail is concave relative to the grinding wheel frame, the diameter of the tapped taper is drum-shaped; otherwise, it is ground into a saddle shape.

3) The influence of the parallelism of the two guide rails on the precision of the tap diameter. There is no error in the V guide rail, and the flat guide rail is inclined in the longitudinal direction. As shown in Figure 2, the workbench moves to a certain position along the bed rail, the inclination angle is a, and the center of the tap moves from the O point to the O1 point, causing the radius error to be d≈H·tga=H· ∆

l Center setting H=300mm, l center=300mm, ∆=0.05mm

Then d = 300 × (0.05 / 300) = 0.05 mm.

It can be seen that the parallelism of the two guide rails has a considerable influence on the precision of the tap diameter. At the same time, the reason why the Model 7901 is more serious than the Type 79 "live flat" is due to the structure of the bed head design. The Model 7901 has been modified by the metric system, and the height H of the rail surface to the center of the tip is increased by about 20 mm. It can be known from the center of the formula d=H·∆/l that H is proportional to d. Therefore, in terms of rail wear, the Model 7901 is more prone to taper roundness error than the Model 79.

6 The influence of the tailstock After long-term use, the matching clearance between the sleeve and the tailstock shell will increase due to wear, causing the knife to be used during the grinding process, resulting in a medium diameter error. The clearance between the repaired sleeve and the tailstock housing should be within 0.008 mm. In addition, the parallelism tolerance of the tailstock sleeve axis and the table movement is 0.02/100mm.

7 The coaxiality of the screw and the mother of the table and the parallelism with the direction of movement of the table are caused by the different axes of the screw and the nut, causing the transmission to flicker. Because it is not parallel with the longitudinal guide rails, the resistance of the guide rail is large and small, and the table changes slightly during the movement, causing periodic errors.

8 Influence of transmission chain error The motion error caused by the wear of various transmission parts such as gears and universal joints in the headstock of the headstock and the eccentricity error during installation will cause the angular velocity of the tap to be uneven, which affects the tap. Medium diameter accuracy.

In actual work, errors often occur as a result of several factors. For example, the solution to the 7901 “live flat” problem is this. Although there are many factors influencing, it is only certain that one item can be found in the repair process, and one item can be solved.

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