clearance measures for pin/ bushing

[notme]

I have a pivot mechanism im trying to build which uses a 1.5 inch pin/bronze bushing/cased in a piece of 2"id dom tubing
what I was wondering how much undersize should the pin be to fit in the bronze and allow room for grease without being to sloppy...and also too press the bronze into the dom tubing should it be exactly the same size? or slightly under? I realize I can heat the dom and cool the bronze to make it go in easier but not sure if there should be a difference in size when its at room temp??? hopefully my question is understandable?

 

[JCByrd24]

I've been doing some reading on this lately as I'm a beginning hobbist machinst (engineer as my day job). You can find the correct answers in books or tables online, but I'll give you my take on what I'd do. Typing it is easier than actually getting there for me. I've come to understand the difficulty of both measuring IDs with calipers and hitting measurements of around 0.001" or so. It sounds like the pivot is not super critical so a couple thousandths would be about right for the pin to bushing, probably has much as 0.010" would be perfectly adequate depending on what it is. If it were rotating it'd be a little tighter from my reading like 0.001". For the bushing to the tube it's much more critical, there are a few tricks if you go too small on the bushing though. Your thought of exactly the same size would theoretically give you a very light press fit that would almost certainly prevent it from slipping compared to your other fit. You don't want to be more than 0.001" oversize on the bushing or it'll be a real pain to press in, a couple tenths would like be the book answer. Getting here is tricky, I'd be sneaking up on it very slowly, using the first 1/16" or so of the tube or bushing as a test area. If you go a little too small and it's slips you can knurl the bushing or just center punch it in a pattern around the bushing.

 

[SandburRanch]

If the bushing has a 0.001" press fit that 0.001" will need to be compensated for when the I D of the bushing is machined or the pin will be too tight. A thousandths per inch of diameter clearance will work for a pin.

 

[KWentling]

I'd go .001-.002 tight with the bronze bushing and allow about .005 clearance to the pin. 35 years a machinist.

 

[beeforty]

I'd go .001-.002 tight with the bronze bushing and allow about .005 clearance to the pin. 35 years a machinist.

Yepp! 40 years in aircraft maintenance and and the the machinists were always making the bushing a tight fit. Otherwise the bushing being the softer material is wearing on both the inside and the outside surfaces.

 

[Tractor Seabee]

They make adjustable reamers to clean and ream bushings after pressing shrinks or distorts them. I agree on the clearances mentioned by others. HF has a pretty good set of reamers that don't break the bank. I am a shade tree machinist but this kind of stuff we do is not considered critical. I do have inside and outside micrometers and dial indicators.

Ron

 

[4570Man]

I make them as tight as I can get and still push together by hand. I like to make the inside piece first and polish the outside. Then I bore the outside piece about .003 undersized and hone it out. The is makes a smoother running bushing than i could do on a lathe alone.