Press Fit Question

Laredo7mm · Mar 28, 2005

How much undersized do you make the whole if you want to press fit a pin? I have always just kind of fudged it, but I was wondering if there is a standard undersize that I should use.

Inparticular, I am looking at press fiting a 0.250 pin into a whole, if that makes a difference. I hope 0.002 is enough because I already have a 0.248 reamer.

TIA

scfishr · Mar 28, 2005

I am looking at a mechanical trades manual,

It recommends for up to 1/2" dia, a .001 press fit,

Hope this helps.

A .002 fit would be very tight.

adammichael · Mar 28, 2005

According to the Machinery Handbook 22nd Edition, from .001" to .0025" per inch of diameter, .0015" being a fair average. So it would be about .0006" for a 1/4" hole. .002 would be way to much.

Ordinarily the allowance per inch decreases as the diameter increases. A 2 " diameter may be .004 where as an 8" diameter may be 9 or 10 thousands.

What the hell are you doing now!?

Michael

Laredo7mm · Mar 29, 2005

Thanks for the info guys. Amazingly even after being an Engineer for almost 10 years, I still don't own a Machinery Handbook.

Well, I will have to try to force it or fuzz it. I can wipe the pin a bit and dust off some material.

What am I doing now? HeHeHe...just wait and see. If all goes well I will bring it with me to the Badger show. I have a couple things going on. Nothing earth shattering, but still kind of cool. Now I just need to wait on the UPS man.

scfishr · Mar 29, 2005

If you have no other option than to use the .248 reamer

You could, theoretically, put the pin in the freezer(will decrease dia)

and warm the object that you are going to pin to say 200 deg f

be sure to work fast as the items will normalize to room temperature fairly fast.

can`t guarantee anything.

By the way, I am not a knife maker, just happened across this thread and do this kind of work fairly regularly. Not trying to be a buttinsky

severtecher · Mar 29, 2005

Scfishr has a fine idea.This is how a horizontal stabilizer is attatched on a Learjet. We used to put the pin , about 1.5", in dry ice for an hour then drive it in with a 10X rivet gun. Some fun.

Chiro75 · Mar 29, 2005

Press fitting a pin.... hmmmm... my guess is a balisong. And, Sean, are you planning on going to the Novi show? I think I'm going to go on Saturday and check it out, so if you wanted to carpool out there or something let me know...otherwise if you go and I run into you I'll say hello! I have to go and harass Kim Breed for a while!

polarbearforge · Mar 29, 2005

It depends on the material it's being pressed into. I regularuly press fit dowel pins and punches at work. If it's being pressed into a hardened piece, usually 0.0002-0.0005 press is all I leave. If it's mild steel or aluminum, something soft, I might leave between 0.0005 and 0.002 for a press fit. These sizes for are for 1/4 " dowels and punches about 3/8" and 3/4".

The finish also plays a role. Did you drill the hole with a 0.248 drill? If you did, the hole isn't 0.248, it's a little larger. That's the way drills are. A sharp reamer leaves a very nice finish and a round hole. Drills leave an ugly hole. Think of a drilled hole as similar to a tapped hole. There will be peaks and valleys just like threads, though they will not be consistant with a drill. When you press fit something, you swedge the peaks into the valleys. If it's a really coarse finish, you might be able to press fit a pin once, but if you knock it out, it will almost be a slip fit next time.

Jamie