Anybody disassemble a Starrett 120 caliper?

The 120s have an open rack which does tend to accumulate junk and swarf, which makes the readings erratic.

Basically you just take it all apart, and save all the pieces. I forget exactly how the plastic bezel and lens come off. I think there may either be a small screw, or a hole that one inserts a wire into.

Then you need a small puller to remove the hand from the pinon gear shaft. I use a small clock hand puller, but you can improvise by prying straight up with a lever of some sort. Pad the face of the dial to prevent the fulcrum from digging in.

There is a tiny anti-backlash gear that is two parts with a small wire tension spring that holds the two parts together. Don't loose the spring.

The pivots in that caliper are mostly jewelled. You can take out the various gears and clean them in a beaker of solvent like alcohol in an ultrasonic cleaner. Don't put the painted dial or the plastic bezel or lens in the solvent.

The body of the caliper comes apart straightforward and the rack unscrews from the body. When assembling the holes in the rack are designed to be a bit oversized so you can install the hand nearly at zero when the caliper is closed, and then shift the rack a tiny bit and have it time exactly to top center.

The rack of course also should be carefully cleaned and all the bits of junk picked out. Sometimes an ultrasonic will not remove the stuff that's really jammed in tight.

Best to dismantle something like this in a large open flat box, so the bits cannot escape and go cavorting off into the carpet or under a bench.

If you do loose anything don't despair, call starrett as they sell replacement bits. I had a 120 that had a tooth knocked off one of the small gears, and was able to purchase an inexpensive replacement from them.

Jim

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