Machined fit?

[Jeepwidow]

When slipping two pieces of metal together (one inside the other) what should the tolerances be? Basically its two machined parts that join with one cylinder going inside the other, then bolting down with the flanges. It’s a drive train component and I don’t want slop in there when it’s all put together. I do want them to slid on, with out force (no pressed fit or beat it in fit). Any help would be appreciated.
Chris

 

[bvasa]

Take a look in Machinery's Handbook under cylindrical fit tolerances, and there'll be a range of diameters for a given fit tolerance. It sounds like you want a locational-slip fit.

If you don't have access to the book, post your joint diameter and I'm sure you'll get a couple interpretations of what the tolerances should be.

 

[Tmoose]

Assembled concentricity variation must be appropriate to maintain the individual components' balance after assembly, and is based on service speed.
Stuff that goes wheel speed (<1000 rpm?) probably only needs centering better than 0.005 inch.
Stuff that goes engine speed may need centering and fit &quot;better&quot; than 0.001 inch.

A &quot;tight&quot; fit that moves the part off center 0.005 is going to be a problem.

The fit may establish the initial centering, but the clamping force provided by the bolts is what keeps it alive.

A 426 Chrysler Hemi flywheel is held on to the crank by 8 bolts torqued to 80 lb-ft torque. The holes in the flywheel are &quot;clearance&quot; holes. The flywheel is centered by a snug fit (<0.001 inch clearance?) on a true running pilot diameter. There are NO DOWELS in that joint ! If the bolts were torqued to 10 lb-ft the joint would fail in one or more ways, possibly in less than an hour.

 

[enginesrus]

Think of it this way. If you have a hole that is say .5 inches diameter. And then take a pin that is .5 inches diameter. That is a light press fit. Depending on the finish on the two items. If the pin was .0005 under it would be a slip fit. Finish and coeffients of expansion play a role too. And it depends on the diameters of the parts, and what kind of fit you want. Like others say see machinerys hand book.

 

[oldfart2]

Hi Chris,
There are several things to be considered here, if you can supply some of the following I may be able to help.
What is the part we are talking about, What diameters are you using, how long is the joint going to be, is it a rotating-reciprocating (axially or rotary) or static joint, if rotating at what revs, is it lubricated, what are the material in the parts?

Regards
Paul H

 

[Romefu12]

jeepwidow;
I believe there are many good replies to your questions. I would have to agree with oldfart 2 that there are many things to be considered especially when talking about 2 cylinders or a cylinder and a pin including lubrication, fixation, joint design and material used. There are other considerations as well including temperature transients. When dealing with temperature as a rule of thumb a 1.00 inch bore will expand .001 inches for every 100 degrees over room temperature(to a point) so your design tolerance depends greatly on the application.

Hope this helps

Romefu12

 

[automatic2]

try .0015 clearance to start with, then add a thou on for every inch of shaft diameter. That should give you a ball park. If the joint has to come apart in the field for any reason, then start off with .002-.005 clearance.