Shims Appplication

[CodeRed7]

Hello,

My plan is to attach a potentiometer shaft to a gear bore using a shaft retaining compound. The shaft diameter is 0.1248"/0.1245" while the gear bore diameter is 0.126"/0.125", which gives a clearance of 0.0015"/0.0002".

Due to the clearance, I am concerned with keeping the shaft concentric with the gear. I was suggested to use shims in order to correct this issue, and was wondering what the best way would be to use them, and if this would be the best solution?

 

[Jboggs]

Sounds pretty tight to me. What level of concentricity is required? And why?

 

[CodeRed7]

I don't have an exact level of concentricity required, I just need the shaft to be centred enough within the gear so the gear can run smoothly.

 

[Jboggs]

I doubt if you're going to get much better than you have now, which in most cases is more than adequate.

 

[Tmoose]

So you restrain the potentiometer housing from turning to some degree, and the gear will support and drive the potentiometer?

I'm guessing the bore in the gear will not run nearly that true, depending on the hardware down the line.

A stiff ("rigid") pot support will cause the input shaft to strain against a rigidly held pot.
There are times in life when compliance/flexibility is required.

 

[tbuelna]

What kind of shim would you use to fill a .0002"/.0015" diametral space between a .125" nominal shaft and bore? I cant see how you could machine such a shim from metal. An anaerobic adhesive like Loctite would provide adequate bond strength if applied correctly, its shear strength is around 5ksi. And the connection could be made without any stress on the mating parts. But how would you disassemble the parts without damaging them?

 

[Artisi]

Let's come back to the real world, a tubular shim of a nominal 0.125" diameter with a number of wall thicknesses ranging from 0.00075" to 0.0001" thickness - come on now.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)