"DoN. Nichols" wrote in message
...
In article ,
Harold and Susan Vordos wrote:

"DoN. Nichols" wrote in message
...
snip---
Cast iron, itself, is somewhat abrasive, even without the skin,
as are some aluminum alloys. So -- if you are cutting a lot of these
materials, the carbide insert tooling should do most of the job,
followed by a switch to a sharp HSS for the final finish pass -- if you
need a better finish than the carbide inserts are giving you.

That isn't a problem if you use the proper grade of carbide, which many
don't understand. Steel grades (C5-C6, etc.) behave exactly as you
described, and you're sure it's because the material is abrasive. Truth
is,
it's not, but the formulation of carbide isn't proper for the conditions
at
hand. . By using a C2 grade for both cast iron or aluminum, what
appears
to be abrasion quickly comes to an end. Being from the "old school" of
carbide, I know to use Carboloy 883 on stainless, cast/ductile iron, and
aluminum.

Thanks -- this is useful information. Though I was really
talking about the abrasion on HSS tooling, where the hard skin on cast
iron or the sapphire layer on anodized aluminum would wear a groove in
the areas which were exposed regularly to the hard skin.

That brings to mind an experience we had many years ago, when I was employed
at Sperry Utah. The shop had a few Gorton Mastermils (I-22), all of which
were step drive. The brake system was nothing more than a portion of the
bottom of the driven pulley on which a caliper clamped down, inside and
outside. The pulley, being aluminum, was hard anodized, and held up
extremely well, but like any brake system, it needed a rebuild occasionally.
In order to remove the old, worn surface, the area used as a brake was
machined, so it could be re-anodized. The brake pads wore the surface a
small distance away from the edges, so in order to get the cut started, you
had to penetrate the old hard anodizing, which, in that particular zone, was
still 100% intact. HSS wouldn't touch it. Any attempt yielded a tool tip
well ground away, with virtually no affect on the anodizing. Bear in mind,
this is hard anodizing, which can be applied considerably deeper than is the
ornamental type of anodizing. The proper grade of carbide (883) worked
perfectly, although you still had to penetrate the anodizing to get the cut
started. The surface created by anodizing is, indeed, similar to a
sapphire!

Harold