Pressing Issues: What size holes for what size pins.

Wow, Terry,

That was a great bit of work you did for me! Thanks so much. I have to confess, I have a "Machinery Handbook"--can't remember which version but I got it new. I just couldn't make heads or tails out of it because I was in a hurry and also because I didn't understand the terms. With what Terry just said, it makes a lot more sense now. I very lazily asked this question of all of you because was tired of trying to figure it out. Now I feel bad because Terry just did all my work for me. However, you did also give a lot of other information that is probably splattered around the book and you very nicely summed it all up.

The dowel pin that I have is a 6 mm 18-8 SS. +.004 to +.012. I'm pressing it through unknown chinese steel thru a 6 mm hole hardened bearing and into the other side of the chinese steel. The roller bearing would be the most difficult hole size to alter, so the dowel pin may need to be sanded in a 5C collet on the lathe to the proper tolerance as Terry said and I'll sneak up on it with the cloth until it mics right as noted. It can be a pretty permanent installation, but I wouldn't mind being able to take it apart to replace the bearing if I ever had to. There are actually 5 of these that I am making. I have a hydraulic press to do this with. Now maybe with this information I can get this done. Thanks everyone for pitching in to help!

Barry
 
barrydc1 said:
So this is one of those questions where I wish I had been to school for engineering. If you want a sliding fit or a press fit (in this case I want a press fit), how do you know what size hole to drill when you have a certain size shaft or pin to press into it? Or in my case I have a 6.00mm hole and what size pin do I need for a press fit. Are there charts for this or is there a consistent size over or under? I suspect that each diameter has different specifications. How is this determined in the machine shop? This was almost touched on in the last thread I started on making a dowel pin or my own press pin, but in this case I'm wondering if the 6mm dowel pins I have will press fit into a 6mm bearing hole?

Also for future education, how do I know what size holes to shoot for with a specific size pin if I want press fit? Or...what size shaft size does one shoot for with a certain size bearing hole?
Click to expand...

Make sure you drill through holes for your pins. You don't have to ream the press fit hole all the way through unless you want to. If you have a blind hole make sure you either grind a little flat spot on the side of the pin so air can escape or use pins that have a spiral air groove ground in them. A little air pressure trapped in the hole will push the pin out. I have seen it happen. Good Luck
 
Thank you all very much for the information, and the tips. I was successful in pressing the pins in to all 3 holes. I did mic the pins and found that they were all either .2367 or .2366". Using my 5C collet chuck, I ground them down with some 330 grit sanding strip (after covering my ways) to .2361 +or- .0001. This allowed a moderate resistance trying to fit the dowel into the bearing bore, but just barely able to start on the slots of the shaft. Which was a 15/64 over reamed hole. This worked extremely well and I am very pleased with the result. I ought to take pictures of my, now, new roller steady rest. I have my 3" bar of 6061 aluminum all dialed in and ready to go, but haven't had a chance to make chips yet. Tonight maybe. I'll try to take some pictures. I have another question I'll post after doing some research.

Oh, the other 2 holes were for my follower-rest, but I'm not sure I'm going to do the same thing to it, as I think the 17mm bearing my get in my way.
 
You must log in or register to reply here.
Back
Top