"Gwhite" wrote in message
ups.com...
On Sep 13, 7:56 am, "Ed Huntress" wrote:
"Doug White" wrote in message

...





I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm
wondering
what sort of abrasive I should try. Given that annodizing itself is
very
hard, I don't know if normal compounds will touch it. I'm also not
sure
how fine I should start with. This is a one-off, so I don't want to
have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and
possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

Anodizing is, itself, aluminum oxide. I think it's unlikely you'll be
able
to do anything like *cutting* into that surface using other than diamond.
You probably could *scrape* it off with other abrasives, but you'd just
be
tearing the anodizing from the base aluminum.

Just an educated guess...

That was my concern. Somewhere I have some diamond compound I used to
lap a small carbide expander button, but my recollection is that it
was extremely fine. My concern was that it might take quite a while
to lap the aluminum piece, which is about an inch ID and 2 inches
long. I may just have to try that.

Some of the Clover compound is aluminum oxide, and I don't know how
well lapping with an identical hardness compound would work. I
suppose I could try that, and then switch to the diamond if it doesn't
work.

Lapping with equal-hardness compound does work (that's how they do
diamond-to-diamond lapping), but it's reported to be slow and sensitive to
pressure. I have no experience with it myself.

Diamond, in general, cuts fast, grit-for-grit.

Please let us know how it works out.

--
Ed Huntress