On Fri, 29 May 2015 09:12:36 -0400, "Jim Wilkins"
wrote:

"Ned Simmons" wrote in message
.. .
On Fri, 29 May 2015 06:01:20 -0400, "Jim Wilkins"
wrote:


If the concern is that you don't trust your mics, remember that you
have the bearing that's going in the bored hole. Treat the mic as a
comparator and the bearing as your standard. Ideally you want a line
to line fit to at most a couple tenths interference. You can
interpolate the graduations closely enough for that. I'd be more
concerned about the machine used for boring than the mics.

On the other hand, if you just want to be sure the bearing goes in
OK
the first time you can always heat the wheels if the fit after
boring
is too tight. Assuming the wheels are steel, a 300F temp rise will
open the bore .003. If you can get within .001, you should be good.
You do need to plan and work carefully when it's time to drop the
bearing into the hot wheel - the last thing you want is to get the
bearing cocked and jammed in the bore. It doesn't take long for the
bearing to warm up and expand.

--
Ned Simmons

I practiced measuring the setting ring. This Enco 508-00150730 inside
mike doesn't have a good enough feel to repeat to better than half a
thousandth.

The machine is my 1965 South Bend 10L, with a 3/4" boring bar that I
cut and ground a 5/16" square HHS bit for. It's more rigid than any
other boring bar I've used so this is my first go at boring a smooth
hole to a more precise diameter than Oilite requires.

On outside diameters that I can measure to 0.0001" the lathe can shave
a few tenths with a freshly honed bit.

-jsw

Essentially, you do not want the bearing outer race to rotate in the
hole and you do not want the shaft to rotate in the bearing inner
race. You also do not want to have too much of a "press fit" on either
diameter as it is very possible to cause the bearing outer race or
inner race to contract or swell sufficiently to cause it to "bind" to
at least some extent.

If I were doing it I would aim for a hole diameter of the bearing O.D.
to perhaps 0.001 larger and a shaft diameter of from bearing inner
diameter to 0.0005 smaller. If there is concern about either the outer
race rotating in the hole of the shaft rotating in the bearing inner
race than just assemble it with some of that bearing mounting goo.

It is not "rocket science".
--
Cheers,

John B.