Subject: Re: Advice wanted in machining lead

From: [email-masked] (Andrew Vida-Szucs)
Date: Thu, 10 Mar 1994 20:01:13 GMT

In article <[email-masked]>,
[email-masked] (Clive Washington) writes:
|> I'd like some advice as to the best way of machining soft metals
|> like lead.  

	[Snip, exluding the litany of problems, such as:]

	|> Poor finish (tearing).

	LOW speeds and very fine feeds.  VERY sharp tools with edges
	polished.  I've never machined lead, but I have done other
	hard to machine metals (titanium is one of the worst).

	I would try running the lathe in back gear with a 0.002" feed
	and maybe 0.005" or less depth of cut on the finishing passes.

	Use lubricant.  Water soluble oil would be my guess since they
	are thin and conduct lots of heat as opposed to lard oil and the
	sort.

	|> Chip clearance. The chips re-weld to the surface if they go
	|> round past the tool again.

	Same as above.  Gotta go slow.

	|> Metal 'pushing'.  e.g if I drill 2 adjacent holes, the second
	|> pushes in the wall of the first.  I have to drill arrays of holes 
	|> in some
	|> items - it's a nightmare, having to go over the array 4 or 5 times.
	
	Multi spindle drill setup would help, but this is, I'm sure, not
	financially responsible, eh?  All I could suggest is starting with
	small pilots and working your way up, but this is, as you put it,
	a nightmare in time burned.

	|> Burring and burr clearance.

	Not sure what you mean here.

	|> rake angles?  

	Not sure about angles, but my gut says they probably should be
	relatively sharp.  Maybe 10 degree front, 10 degree back rake with
	a round clearance channel ground right behind the cutting edge that
	would give an effective angle of about 30 or 40 degrees at the edge
	without compromising tool stability.  Can't say for certain though.

	-Andy V.

---

From: Doug White <[email-masked]>
Date: Thu, 17 Mar 94 16:12:18 -0500

This may not be practical in many situations, and I've never tried it on
lead, but freezing might help.  I knew a machinist who used to turn things
out of rubber (!) by freezing them with liquid nitrogen.  This made the
stuff hard enough to cut with some (?) precision.  He had to be very careful
to keep his cutting tools extra sharp to avoid heating things back up.
The tools were ground with a LOT of rake angle to work much more like a
knife than a conventional tool.  I haven't tried rubber, but I have had
some improvement in finish on soft plastics by cooling them with the 
spray freeze aerosol used for testing electronics.

------------------------------------------
Doug White
Satellite Communications Technology Group
MIT Lincoln Laboratory
244 Wood St.
Lexington, MA  02173-9108