Mitutoyo Test Indicator Repair
Replacing a bent, broken or damaged center pinion
(The following is an excerpt from our Mitutoyo Test Indicator Repair Manual, page 44)
In this case, we have a damaged center pinion and will need to replace it. The shaft is bent to the side and this will cause the hand to wobble and probably touch the dial surface.
Remove the two screws on the bridge. The bridge lifts off revealing the small center pinion and the hairspring mounted on the hairspring gear. Notice how the end of the hairspring is threaded through the hole in a post and then pegged in place with a conical brass peg.
The center pinion (on the left) has a bent shaft. You may try to straighten it using small jeweler’s pliers, but—more often than not—the shaft will snap off.
The same center pinion (21CAA016 ) is used for all of these Mitutoyo indicators.
If the gears are corroded, you can try using a brass brush. The teeth have to be in good condition for the indicator to move freely and to be accurate. After cleaning the movement, insert the new gear. Make sure that the hairspring does not rub up against the center pinion. It must also float horizontally so that it does not rub against the gear or the bridge, once that is put back on. You can bend the hairspring into position with fine pointed tweezers as needed.
Once the bridge is reattached, the synthetic jewels are oiled and the hand is temporarily put in place. Check that the hairspring works freely and that the hand doesn’t hang up anywhere.
Additional photographs for this section are included in our Mitutoyo Test Indicator Repair Manual.