"Martin H. Eastburn" wrote in message
. ..
Ed Huntress wrote:

I'm not sure what you're saying here, Martin, but diamond turning and
milling cutters are not used on ferrous metals except in very rare
situations. They just don't last, for the reasons Howard has explained.

In production, diamond is use primarily on high-silicon aluminum. Other
uses
include composites, plastics, glass, and other non-ferrous metals.

The development that made polycrystalline synthetic diamond a
near-necessity
in production was the use of very high-silicon (hypereutectic) aluminum
casting alloys in automotive applications. Another one of the early
users
was Mercury Marine, who used it for machining their hypereutectic
outboard
motor blocks. OMC soon followed suit.

--
Ed Huntress


Ed - I generally agree. But I feel the panic is a bit high.

A diamond on a metal base that is spinning contacts the work for a very
very short period
of time. This assumes the tool is spinning and the diamond isn't
massive...

I'm assuming a 'point' of fine atomic level that diamond can do. It is
the touching / grinding
on a fine point. [ remember the Garnet sanding sheets that shatter as they
impact and stay sharp ]
diamond is tougher and stands up to higher pressures.

The 'nano'-second it touches the work it will heat up but starts to cool
down as the cutting arc
is swept. The diamond wicks the heat (being the best conductor - far
better than metals) to the
work base metal the diamond is loaded into. Which gets hot. (a little
anyway).

If coolant is supplied as in mills this would help.

Normally diamond is to expensive to use in a normal work area, other
materials have been developed.
Even special process of near zero degree work has been developed for some
applications.

Saw blades have diamond pressed into slots on the circumference. These
slice through rock and cements...
I have sliced through tons of material. The diamond doesn't absorb into
the host material (the tool)
but I suspect the very highest temps are only at the tip where atoms are
stolen.

Is it simply a matter of cost ? - the carbon is absorbed a little and the
tool becomes used up?

Maybe the data is simply old economics. Diamond drill heads bore through
iron cobalt deposits and
other iron rich layers for many years in well drilling. So maybe research
needs to look at this
again with a different point of view.

Martin

Well, yes, it's economics. In turning and milling ferrous metals, the costs
of using diamond tools can be worked out very neatly from wear-life data
that was compiled decades ago. Using diamond cutting tools in chip-making
applications on iron and steel is very expensive business, and the amount of
it that is due to chemical carbon loss has been quantified. I haven't seen
the data since around 1979 or so, when GE was touting its then-new CBN, but
it's out there.

There are some places where it's been used on steel. I think it was
Pneumo-Precision that was using diamond tools for steel on one of their
optical-grade lathes (built on granite bases) back in the late '70s and
early '80s. The applications were optical or optical-grade turning.

It's not that it doesn't work, and it's true that there are some rare
situations in which it's the way to go. But not in general.

Grinding, honing and lapping are another matter. The same principles apply
but the dynamics and the economics are different. Again, I haven't kept up
with this. The last thing I remember was some data from Sunnen on their
plated-diamond, one-pass honing tools that came out in the early '90s. It's
a bit more complex than the situation faced with chip-making tools.

--
Ed Huntress