On Fri, 29 May 2015 06:01:20 -0400, "Jim Wilkins"
wrote:

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
.4.170...
"Jim Wilkins" fired this volley in
news:mk89h1$mft
:

For something that won't be used much is there a problem if a
bearing
fits loosely in the 40mm bore?

Not TOO much of a problem, so long as you have a 'keeper' to prevent
it's
migrating out of its cavity. That, and so long as the speed is kept
low,
it won't damage the bearing to 'roll' on its outer periphery.

But (cough!) why would you be pounding on the INNER race to remove a
bearing? The access hole at the bottom of the cavity (through which
the
shaft will penetrate) can be only a few-thou smaller than the outer
race,
and it will be retained on that end just fine. Then you'd be able
to use
a proper outer race-sized drift to remove it, were the fit too snug.

Lloyd

The reason is because I'm copying the existing wheels closely in
hopefully better metal instead of re-engineering a heavily loaded
design I don't fully understand. The HF wheels have an 18mm center
hole that catches a snap ring on the 17mm axle. Presumably the solid
metal from 18mm out to 40mm stiffens the wheel rim against distortion.

I could drill three holes for push-out pins and use one wheel to hold
and guide them while pressing the bearing out of another.

-jsw


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