Subject: Soft Material Machining (Was Teflon machining)

From: [email-masked] (Boris Beizer)
Date: Thu, 06 Jun 1996 14:37:45

Back when I was working in the hospital lab (1954-56) I had
to machine a big (10" diameter x 20" high) container made out
of lead.  Walls only 1" thick.  Had to be one piece (except
the cover) to prevent any kind of radioactive material 
leakage.  Had to be very accurate (for lead, that is) +-3 thou.
Again to minimize radioactive leakage.   I had a 24" x 120 lathe 
at my disposal for the job.  I spent a lot more time remelting and
recasting the swarf to start over again than I did machining.  30
years later, in the (MUST BE ON YOUR BOOKSHELF--DOVER PUBLICATIONS)
classical book by Holtzapfel (1810 or thereabout) I read his
recommendations to use sour milk as a lubricant--but if that turned
you off, try dirty water!!!  Holtzapfel, I have learned, besides
being the father of almost all our modern machine tools, is never
wrong.  I immediately tried the dirty water.  Didn't have that
much lead around nor a big enough lathe, but I turned a 3" d x 6"
long bored-out cylinder in a few hours with an inner tolerance of
+-2 thou. Holtzapfel wins again.  
    I couldn't stand the sour milk or wait around for it cure, but I 
tried and found that thinned out yogurt works just as well.  His
explanation for this marvelous lubrication technique is that the 
trouble with lead is that it resolders itself.  The dirty water and/or
sour milk promotes an instant oxidation that prevents the metal from
resoldering.
    Something like that might be going on with soft plastics.  Surely
this is a phenomenon that affects all low-melting temperature
stock.  Instead of lapped bits, it might be just a question of finding
the right lubricant. Fiberglass mold release?  Sour WD-40? 

Boris
   
Boris Beizer

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Dr. Boris Beizer                                  Seminars and Consulting on
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From: Bob Frazier <[email-masked]>
Date: Thu, 6 Jun 1996 21:12:20 GMT

Boris Beizer wrote:
> of lead.  snip
> 	How about lead bullet lube from a gun store? Alox & beeswax?
Without lube lead bullets "lead" or solder up a bore at high velocities.
	Bob

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From: [email-masked] (Robert Galloway)
Date: 7 Jun 1996 09:46:09 -0600

>the right lubricant. Fiberglass mold release?  Sour WD-40? 

Melting is a big problem with poly(methyl methacrylate) but not with 
Teflon.  Even though swarf can wrap around and mess up your cut, it 
doesn't tend to weld back to the parent metal.  I've never found any 
libricant necessary or helpful.  My Teflon turning has been limited to 
2-3" dia. stuff at aluminum speeds with HSS tools.

rhg