You are talking about a press fit. I would shoot for a hole that is .0005"
smaller than the pin.

The bearing is the next consideration. If you will consult the bearing
specs, you should see that the bearing is designed to have either the shaft
or the housing press fit to the bearing to take up the slop. This depends
on the permissible slop and the amount of change that will occur when the
bearing heats up and swells at operating temp.

On a surface grinder where you want to keep wobble as near to zero as
possible, all of the cumulative tolerances need to me considered to select
the proper fit. If you are talking about a less critical application, then
the running clearance can be looser.

If I understand your application correctly. you want the pin to be fixed in
the hole a little snugger than the pin to the inside of the bearing.

--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.


"John2005" wrote in message
...
Hi everyone,

I would like to ask if anyone can please recommend a tap fit hole Min.
& Max. tolerance for a 3/8" hardened steel dowel (.3751" Min to .3753"
max OD) ? The pin will be tapped into 4140 Pre-hard steel.

The pin is being tapped through a bearing housing, 1" OD X 1.5" long.
The bearing housing fits between two upright supports and there is one
drawn cup needle bearing pressed into each of the upright supports. I
want to insert the dowel pin through a bearing at one end, and then
tap it through a hole in the 4140 housing and on through to the
bearing at the other upright support. The housing and pin will rotate
together, and the pin rotates in the bearings.

I will probably build simple fixture to locate and hold the housing as
I tap the pin through. I want it to be fairly easy to tap the pin
through, so assembly goes smooth, but I don't want the housing to
rotate on the pin, the pin and housing must rotate together in the
bearings.

In order to get a nice easy tap fit, can I have a very small amount of
interference to do I need some clearance ? I was going to shoot for a
hole size of .3748" Min. to .3751" Max.

I'm just curious what's usually recommended for an easy tap fit.

Thanks
John