Thread: Installing press-fit bushings

Tweet

I went over to my baby brother's shop today (I think I once mentioned that my "baby" brother is 71) and found him struggling to install a press fit bushing into a small motorcycle frame. I figured he wasn't having much success by the volume of the cussing I heard.

We got into an intellectual discussion (it could happen) about freezing the bushing and whether to heat the part with the hole, and if that is the way to go.

I can see freezing the bushing since doing so should cause it to shrink, making it possible to press it into a properly sized hole. Where the conversation got loudest and nastiest was whether heating the part containing the hole would would cause the diameter of the hole to get larger or smaller. I say smaller. He disagrees.

It seems to me that if you take a part, say a steel nut, and heat it up, it's gonna swell a microscopic amount and swell in all directions. I mean, it will be thicker and wider and the hole would be smaller. Like frying a doughnut...... (How's that for a dumb a--ed example?)

So, is freezing the bushing and heating the hole is a self defeating exercise?

........ I guess I probably ought to go outside and find something to do instead of sitting around pondering life's great mysteries.

Jim

no it is not.. it works.. this is how you can do it that is the way to put seats in alum heads i run .002.5 to .003 press on sleeves in blocks i have used dry ice and i do not heat the block but on short press fit you can heat the bore is will open it and freeze what ever you want to press in the bore it works but you need to move fast

by coeffecient of thermal expansion the circumference of the hole (circle) expands as a straight line would, in a "linear" fashion? now you may even calculate it?

It looks like you gents have cost me a case of beer.

Well, thanks anyway, I guess.

Jim

Big Tracks---I'm with you---That heating something to make the hole get bigger is hard to get your head around. If you think of it in terms of heating the metal around the hole, it seems like the metal would expand and make the hole grow smaller.---But----It doesn't work that way. Exactly the opposite in fact. Think of the hole as having a circumferance of a given value. When you heat the metal, the metal expands, and the circumferance has to get longer because the metal is expanding. When the circumferance gets longer, then the diameter has to get longer as well, and it does.

Hey, that makes sense, Brian!

However, I'm not admitting it to the brother.

Thanks,

Jim

In industry this taken to extremes at times. How about 25 mils radial interference on a 4.5 inch diameter shaft? Easy, heat the female part to 750 F and cool the shaft to -320 F and they just slip together, well with some tooling.

Kitz

Originally Posted by kitz

In industry this taken to extremes at times. How about 25 mils radial interference on a 4.5 inch diameter shaft? Easy, heat the female part to 750 F and cool the shaft to -320 F and they just slip together, well with some tooling.

Kitz

Betcha my little garage isn't near big enough to hold the heating and cooling equipment is it????

Okay, boys, I give up. I'm wrong.

Soon as the rain stops I'm going to go back to Brother's place and present to him a case of adult beverage.

I'll do it, but it ain't going to be easy.

Thanks for setting me straight.


Jim