How to tolerance a 4" diameter hole for a sleeve

[hikingff77]

So I am trying to get the drawing 100% for release and I want to make sure I'm on the ball here.

I have an aluminum block that will have a steel sleeve inserted (FN2 press fit) into it.

There is no load on the sleeve except the initial press in, it is there to prevent the aluminum from wearing by a piston.

So what we came up with is the sleeve being +.003-.000 and the hole in the aluminum block to be spot on to -.002" undersize.

Thoughts on this? I'm looking for an FN2 style fit.

Thanks.

 

[KENAT]

What do you mean 'spot on to .002" undersize?

Fundamentally you still need a tolerance on it, you may be able to make the tolerance very tight but if you can get an accurate enough measurement device you'll almost certainly discover you aren't 'spot on'.

How about the old trick of heating the block and even cooling the sleeve before assembly to reduce interference during assembly.

I forget the expansion rates for these 2 dissimilar metals, and I don't know your service condition but there may be a concern that at high temperature your press fit will be reduced.

Do your proposed values still correspond to FN2? Have you verified by calculation that FN2 is the appropriate fit for you application?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[hikingff77]

Thanks for getting back to me.

The process for this part is a piston being pressed into this chamber and material coming out of the bottom. Kind of like a playdough toy.

I'll have to check out the expansion rates of the material to know for sure on that end. Researching that now.

From my understanding a FN2 is a medium press fit, not intending for diss-assembly. Which is exactly this case.

 

[raulob72]

The tolerance should be at .001 per inch so it coulbe 3.996 minimun,my .02.