"DoN. Nichols" wrote in message
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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.

I've yet to find a situation where HSS would perform better than carbide
when machining iron. Please keep in mind I'm a strong supporting fan of
HSS----but it, too, has limitations.

Harold