Dan Murphy wrote in
:

Anthony wrote in
:


I'm gonna quibble with this a little. Although I'm sure Anthony
already knows this, someone else might find it interesting. A PCD
tipped tool won't give you the best possible finish in Aluminum. PCD
or Poly-crystaline diamond is made up of many diamond crystals. A
single crystal diamond, usually a natural low grade gemstone, will
give the best possible finish, since the cutting edge can be lapped to
a flawless condition. With a PCD tool there is some "un-eveness" due
to the multiple crystals. I have a polygonal mirror on my desk that
was face milled in Aluminum with a natural diamond tool. Also, video
tape recorders have drum heads that are turned with a single crystal
tool. Look inside a VCR. The head is aluminum and that is a turned
finish. Pretty amazing. Thing is, you need a damn good spindle and a
very good servo system.

Dan



Agreed Dan, however, within the budget of just about anyone, PCD would
be the next choice. Monocrystal diamond tools in any useful size are
*extremely* expensive. We do use some, but only in applications where
the specific advantages they offer are absolutely required.

PCD grain size (PCD Grade) will determine, to a large degree, the
surface finish you get. Using a fine grade (say GE 1500), will provide a
better finish, but really should only be used for light finishing cuts,
as you have much smaller diamond crystals which are easier to rip out of
the binder along the edge. However, you do get a much smoother edge on
the tool, with smaller binder gaps between crystals, hence better
surface finish. You want to use a very coarse grained PCD tool for
roughing operations. The crystals are larger, but the binder has a
better grasp on the crystals, so they aren't as easy to rip out. You
will have a rougher surface due to the larger gaps of binder between
crystals, however.

Unless you are doing mirrors, or some automotive/electronics/NASA type
stuff, the differences are unnoticable to the average machinist. You can
really only see the differences when doing microscopic inspections of
the surface.





--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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