Repairing a Starrett 446 analog digit depth gauge

[BrokenSpoke]

I'm somewhat puzzled how this thing comes totally apart and how the thimble turns the main gear. I purchased this on ebay. When I received it, it had hesitation when turning but seemed accurate. I tried to take it apart to see if it was dirty or another issue. However, once I backed out the thimble and threaded it back in, it stopped spinning the digits. I then took it apart more and tried to adjust the digit gear mechanism thinking it had become detached from the main gear. It somewhat works, but does stop rotating the main gear which causes the numbers to stop advancing. I can literally push a screwdriver very lightly on the main gear while turning the thimble, and that little bit of force causes it to stop spinning. Basically the tension of the digit gear mechanism is enough to cause the main gear to stop spinning while the thimble moves smoothly. Not sure what causes the needed tension between the main gear and the thimble shaft.

I tried to register on Starrett's site to see the 3D exploded view, but all their 3D links come back with some generic "You have a pending request in queue. It should be resolved soon."

Anyone have a clue how to tear this down further or what might be the issue?

 

[Shiseiji]

Mr. Pete did an episode on the 216 micrometer that might be helpful.

 

[BrokenSpoke]

I literally just now got it apart. The long black hollow shaft unscrews from the base (which is brass). It was tight, but held it in my milling vice and some plyers got it loose. I did find a crack in the PLASTIC (can't believe Starrett uses plastic) main gear. That was causing some skipping. In addition, the main thimble shaft had a bur on the end which was causing too munch tension... I got it out with some real fine paper spinning on the lathe.

I have an email in to Starrett to see if I can order that gear. Their customer service over the phone didn't really know what to say since its not in the parts list for the 446

I really hope this $400 (new price) piece of precise measuring equipment doesn't have a non-replaceable plastic part... that would suck.

 

[SLK001]

It looks like that gear is only available in the "base sub assembly" which is not available from Starrett. To repair your gauge, you're going to have to make one, or repurpose another gear.

 

[llamatrails]

I've bought a few analog digit mics from Starrett and Mitutoyo on eBay. One skipped with a broken gear like yours, and I returned it to the seller since he said in the listing that it was working.

If the listing said it was working, then eBay will help you, even if the listing said no returns.