Press Fit Slipping

[Whyemier]

I turned a small cast iron flywheel (3" x .375) for a project I'm doing. I decided to band the circumference with brass. I bored the brass with a press fit of (.001-.0015) and pressed them together. This was fine until I was facing and turning to true the brass up. I didn't take into account the different rates of expansion under heat from working the metals. The brass spun loose from the cast. Hmmm. I can still redo it but...what would be a good press fit for this band? press fit with a .002 or better and heat to expand before pressing. Or would this spin on me too? I'm not set up with coolant for the lathe so that's out. Perhaps a slower feed and speed??

Anyone have this problem before and would know the best approach?

 

[mmcmdl]

Sounds like you didn't have a .0015 press fit to begin with . Perhaps the flywheel shrank if you didn't use coolant ? You could possibly run a knurl on either part , use some Loctite retaining fluid and heat up your ring ?

 

[Bob Korves]

+1 on using Loctite to reattach the brass band -- without changing the fit or re-machining it. Use red or green, preferably green. Carefully clean the parts so there is no oil on them before using the Loctite. Take it easy when you machine the brass afterwards.

 

[Groundhog]

From Loctite web site - "
LOCTITE 603



Retaining Compound - high strength. Ideal for bearings. For use on close-fitting cylindrical parts. High oil tolerance."

 

[intjonmiller]

Did you let the parts in both cases cool before measuring?

 

[tertiaryjim]

With a 3" dia you probably should have .003" to .004" interference with a thin brass ring. Perhaps more!
Diameter,Material, Stress, and Thickness are the main considerations.
Machinist Handbook can be your friend.
As long as you don't stress it or heat it much the Loctite should hold.

 

[mattthemuppet2]

ditto Jon's Q - it's amazing how much things can move a few hours after you finished machining something. Knurling would work or a poor man's option that I've used is to center punch around the male part, then put some loctite on it. Only done that on relatively small things though.

 

[Andre]

For a 3" diameter, .0015 is a very light press fit. You could get away with twice that, or even a little more if you heat up the brass band to expand it.

 

[4GSR]

Put in a .005-.007" heat shrink into the two parts. Wouldn't take much heat 275-300 deg. F. Drop on, let it cool and machine to cleanup.

 

[Whyemier]

Thanks everyone. I'm machining a new one this wknd and will leave .003-.005 for shrink fit.