Shrink Fit tolerences Again

[ozzie46]

I'm milling my "Simplex "wheels out of aluminum and going to fit steel tires on them. My question is what should my wheel dia end up to get a good shrink fit from the steel tire? The wheel will have a dia. of 4.125. So what should the ID of the tire be? 4.124, 4.123. less, like 4.1245?

The tire is being made from some steel used as Hyd cyl. ram tube.

I have looked at the machinist handbook and to be quite honest can't make heads or tails of the limits and fits table. I don't know why but it just seems confusing to me. Its probably something simple in how to read it that I've overlooked but I don't know what

Ron

 

[peatoluser]

Hi Ozzie
it's been a while since i had to any shrinkage fits but rule of thumb ,if I remember correctly, was 1 thou per inch dia. i.e. you would need to bore out your tyre to 4.121. and don't overheat the tyre - a maximum of dull red. take it any higher and the tyre won't try to shrink back to it's original size so you won't get as tight a fit as if you had taken to just above the tempering colours. But i only ever had experience of fiting steel over steel. What would happen to an alloy wheel if you used the same tolerances i don't know, and i'm as curious as you to learn more. 'cos i have some 5 inch dia. alloy bar and it never occured to me to turn the wheels for my tender from it and fit steel tyres. You may just have saved me 90 quid for the castings!

 

[ozzie46]

Thanks peatoluser,

I will be heating the tire in a cast iron skillet on a electric stove and putting the wheel in the freezer to chill it . I will leave it in overnight to get it as cold as possibly. then assemble them.

I don't have a large enough torch to heat the tire to dull red. If I chill the wheel I think it should shrink enough to slip on.

Ron

 

[arnoldb]

Hi Ron

Peotoluser is on the mark; it comes in at 4.120 to 4.121. If your rims are thin, rather go for a slightly lighter fit, otherwise they might break when contracting.

You shouldn't have a problem with heating in a skillet (or in a domestic oven at max) and the wheel in the freezer. Aluminium expands (or in this case contracts) more than steel, so should give you good clearance for the fit. You might have to be quick when pressing together though; the Ali will soak up the heat from the rim very quickly.

Regards, Arnold

 

[ozzie46]

Thanks Arnold.

The tire will be approx 1/8 in thick at the tread and 5/16 in thick at the flange, so maybe 4.122 would be better.


By the way in case I didn't tell you before I have really enjoyed your posts. I have learned a lot from them.


Ron

 

[bob ward]

The other way to look at the problem is figure out how hot the rim will have to get so it will easily slip over the aluminium wheel. The coefficient of linear expansion for steel is .0000073" per inch per °F, which means that the diameter of your 4.25" rim will grow by .0031" for every 100°F of heat.

A 500°F heat in your kitchen oven will increase the rim size by .015", take away the 4 thou interference fit and you will have .011" fitting clearance.

Similarly the aluminium coefficient is .0000123", so chilling it by 100°F will give you another .005" fitting clearance.

You probably know this, but its easier to pick up a cold wheel and stab it into a hot rim rather than doing it the other way round.