From: jmorton@euler.Berkeley.EDU (John Morton)
Newsgroups: rec.crafts.metalworking
Subject: Re: Advice wanted in machining lead
Date: 10 Mar 1994 18:10:50 GMT

In article <pazcw-100394123957@ppacwz.nottingham.ac.uk>,
Clive Washington <pazcw@uk.ac.nott.unicorn> wrote:
>I'd like some advice as to the best way of machining soft metals
>like lead.  I occasionally get jobs to make small items for medical
>radiology and have been turning, milling,and drilling lead for a while,
>but always seem to get poor results.  Some of the problems:
>
>Poor finish (tearing).
>
>Chip clearance. The chips re-weld to the surface if they go
>round past the tool again.
>
>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.
>
>Burring and burr clearance.
>
>So, should I be using a coolant/lubricant?  What cutting speeds are
>appropriate?  rake angles? Tool tip radii?

I machined a lot of lead at the last place I worked.  Here are some
observations:

	When drilling, dub the end of the drill as you would for 
	brass.  The bigger the drill, the more important this is.

	Paradoxically, for single-point turning and boring, what
	works best is a very keen tool with a lot of rake, usually
	with a radical curl for a chipbreaker.

	Douse the cut in lots of kerosene.

	Observe the direction in which the chipbreaker throws
	the chip.  Sometimes a different geometry can toss it
	away from the work so that it has less of a tendency
	to stick to the finished surface.

	Plan ahead by leaving extra length to grip in the chuck.
	Lead is so inelastic that it doesn't maintain jaw
	pressure.  I like to use those chuck jaws with big
	gnarly teeth, and bury them in the workpiece.

	Once everything is working properly, you should be
	able to take a cut as deep as the tool edge.  I once
	had a block the size of a suitcase set up on a horizontal
	mill, and took 1/2" deep cuts with a 6" diam. shell
	cutter, at the fastest feed available, probably 20 in/min.
	It would even cut OK while I was holding the rapid lever :-).
	The chips rose up in a fountain right to the ceiling.
	It looked so great that I invited my family to come
	and watch :-).

John Morton					University of California
jmorton@euler.berkeley.edu			Mechanical Engineering
{decvax,cbosgd}!ucbvax!euler!jmorton		Machine Shop