Southbend 9a: micrometer stop problem

[dhomrigh]

All,

I have a SB 9a lathe (from 1960). It has a micrometer stop which I've been trying to use. However, when I am operating the lathe, even slight vibrations cause the "thimble" part (if thinking of it like a micrometer) to rotate, which completely destroys any precision/repeatability. There doesn't appear to be any mechanism for locking it at a particular value (again, like a micrometer). I'm sure I'm missing something obvious but I can't figure it out (nor find any mention of it in a forum).

Thank you for any help,

Darren

Edit: I've posted a few pictures. The nut on the bottom and the hex head on top both seem to only lock the stop in place. The oil plug thumb screw is just that and can't be used to lock the thimble. I haven't taken the covers off the ends to look at it, but I probably should.

 

[Ulma Doctor]

I’m not familiar with the 9a micro stop’s construction.
But, if the construction permits, it may be possible to add a small spring to the thimble. The spring would put pressure on the thimble and mitigate the thimble rotation during operation.
Some stops have a (knurled) locking nut, built into the construction.
A picture of your stop may help to come up with a solution

 

[piper184]

Maybe this will help:

 

[SLK001]

My guess is that you're missing the brass shoe. That thumb wheel knob DOES lock the thimble in place.

 

[piper184]

I think the thumb screw that says to remove to oil is actually the lock screw. You might be missing the shoe that makes contact with the wheel.