Centering Work in Four-Jaw Chucks

How do you center work in a four-jaw chuck using a dial test indicator

(DTI)?

Here are the steps:

1. Use the concentric rings on the chuck face to center the work by eye.

2. Set up the DTI as shown in Figure 7–61 (a).

3. Align any one of the chuck’s jaws with the axis of the DTI plunger and rotate the DTI scale to set it to zero, Figure 7–61 (a). The black dot on the chuck illustration is to make it easy to keep track of the starting jaw.

4. Rotate the chuck exactly one-half turn, read the DTI dial and adjust these two opposite jaws by one-half the DTI reading to center the work. Use the DTI to make this adjustment, Figure 7–61 (b). The work is now centered between these two jaws.

5. Rotate the chuck back and forth one-half turn to verify that the work is centered between these two jaws. If not, repeat steps 1 and 2.

6. Rotate the chuck one-quarter turn in either direction to put a new chuck jaw parallel with the DTI probe, zero the DTI scale, Figure 7–61 (c).

7. Rotate the chuck one-half turn in either direction, read the DTI and adjust these two jaws one-half the DTI reading so as to center the work between these two jaws, Figure 7–61 (d).

8. Verify the work is centered by slowly turning the work through a complete turn while observing the DI. Repeat the above steps if needed.

With practice it is easy to center work to less than 0.001-inch eccentricity in under a minute.

Copyright © 2004 Metal Arts Press