Starrett cleaning and lock question

[Frodge]

I took apart my mic today to clean. Should the locks be replaced at some point? How do you service the locking thumbwheel?

 

[Bakafish]

I assume you are asking because it doesn't work? When asking for help, please describe the problem you are having clearly.

 

[Frodge]

It didn't lock tightly. All the parts are there. I have it back together. Is it ok to put a small drop of oil on the roller pin and in between the thumb wheel and inner plate? It was very stiff to turn before that. What is a way to increase tension on the lock. Pretty tight now but a little more will be better.I still don't understand how turning that ring forces the cam into the narrow part of the slot, if the inner and outer ring turn independent of each other.

 

[Bakafish]

The way that sort of lock works is the outer ring rotates the small cylindrical pin so that it rolls up the flat ramp. As the pin moves up the ramp, it forces the gap in the inner ramp ring to close, constricting it around the anvil shaft. The inner ring is keyed, there is a raised area where it engages to the body, so it shouldn't rotate and when it grips the inner shaft everything should lock. That gap in the inner ramp ring needs to be clean, swarf in there will prevent it from closing. The little pin needs to be round and large enough to engage easily with the outer ring when in the rest position, and the ramp surface needs to be smooth and flat.

That pin and ramp both look a little worn from use. Lapping the flat ramp area, and finding a small hardened pin to replace the existing one, assuming it is as bad as it looks from your picture, should restore the functionality. Starrett is good about supplying replacement parts, so you may still be able to get OEM stuff if it needs replacing.