On Mon, 18 May 2009 00:45:01 -0500, Tim Wescott
wrote:

On Sun, 17 May 2009 21:21:33 -0700, Michael Koblic wrote:

Lapping seems to be a term that encompasses several different processes
of similar nature.

I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve
this: From dedicated lapping compounds obtained in Auto part stores
(which here nobody has heard of) to mixing up a scouring powder with oil
to make a lapping paste. It brings up several questions:

1) When does lapping stop and grinding starts (Permatex make a "valve
grinding compound" which some people use for lapping)? 2) What is the
maximum/minimum grit suitable for lapping? 3) Why isn't using ultrafine
steel wool/Scotchbrite pad "lapping"?

FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings.
Not having anything "lapping-like" to hand I mixed up Fast Orange with
oil and used that. It contains pumice and GOK what the grit of that is.
The shaft is smoother. I think.

BTW it is now virtually impossible to get the old scouring powders for
cleaning - everybody is so proud that their product is "scratch free".

While browsing in the Auto part stores I found several cleaning pastes
which contain abrasives. Would they be suitable? Too harsh?

Where's "here" for you?

In the US you can get lapping compound (and diamond grinding/lapping
compound) from McMaster and from Small Parts, Inc.

IIRC, Michael's in BC.

I haven't done any myself since engine rebuilding on the farm days
(decades), but usually it means charging abrasive to a softer metal
form to lap a harder metal. The abrasive embeds in the softer metal,
then the lap (softer is moved across the harder material to improve
finish and fit.

This implies that you wouldn't want to lap a babbitt bearing because
you'd never get the abrasive out, and it'd continue to wear the shaft
it was supposed to protect. Very deformable laps also wouldn't be
effective because they wear the low spots almost as fast as the high
spots.

Brass makes a good lap for cast iron or steel. I intend to use lead
bullets charged with abrasive to fire lap a rifle barrel. There's
lots of other combinations.

The abrasive must be removed completely from the lapped part after
lapping. I have read of abrasives that break down quickly so they are
not a problem, don't know how effective that is.

As far as obtaining lapping compounds, I'd google Clover compounds
British Columbia. Hmmm. Just tried that, there's a supplier in
Ontario, and the stuff is pretty easy to ship. They also have some
info on grit sizes and uses. http://www.newmantools.com/clover.htm

Pete Keillor