On May 18, 5:17*pm, "Michael Koblic" wrote:
wrote in message

...



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?
Greetings Michael,
It's too bad you used pumice to lap your shaft. This is because the
pumice will embed itself into the softer bronze and continue to lap
the shaft. For lapping plain bearings (AKA bushings) the stuff to use
is called "TIMESAVER". You can find it online. It is an abrasive that
breaks down completely and will not keep cutting. It is available in a
sampler kit that contains several different grits of two different
types of compound. One for soft metals like bronze and babbit and the
other for steels and the like. Unlike regular lapping compounds when
this stuff is used the softer material is lapped, just the opposite
when using, for example, Clover Compound.
ERS

Ah. Live and learn. Though the stuff washes off my hands fine. Maybe the
shaft will live...I honestly do not know how much effect it had in the first
place. Anyway, calling it a "shaft" requires a fit of enthusiasm in the
first place.

Now I am still confused: Why go to all this kerfuffle to smooth out a bit of
metal, particularly if it is flat. I see the grits available are anywhere
between 50 and 1200 so one can take pretty big chunks of material. Why can't
you achieve the same result (on a flat and accessible surface at least) with
steel wool/Scotchbrite pad? Or just plain old sand-paper for that matter (if
you are using the coarser grits). How is the lapping compound behave
differently from these other gizmos?

But thanks for the references - I have been able to bookmark the web site
that sells both Clover and Timesaver just in case I decide I cannot live
without it.

--
Michael Koblic,
Campbell River, BC

Lapping is about getting two parts to fit each other, as in lapping
valves into their seats, or pins into holes. Scotchbrite is about
getting parts clean and shiny.