Re: [ATM] Balance, Danyo-san!

[Woodchuck <djv@bedford.net>]

On Fri, 9 Jul 2004 mdholm@telerama.com wrote:

> I am curious, Jerry.  How did you drill and tap that lead counterweight?  I
> tought lead was difficult to do that with because of being so soft.
>
> Mark Holm
> mdholm@telerama.com

There are ways to harden lead, bullet casters do this.  Mostly they
are alloying the lead with antimony and/or tin.  Wheelweights
(scrounge for free from places that do tire work) or linotype metal
are plenty hard already.  You might try casting the threads in,
using a well-smoked piece of ready-thready-rod as mandrel (might
get stuck!).  If you or anyone is curious about this I can research
and post some bullet-casting URLs which will give definite alloying,
melting, source-of-supply info.  There's also a heat-treatment
hardening method for certain lead alloys.  Riflemen want hard lead
because it is more "machinable" when it hits the rifling in the
gun.  Soft lead can smear around, fouling things quickly.  To me this
means that hard lead alloy will also machine better when tapping.
"Better" is a relative thing.  I bet a roll tap would work well
in lead, but don't know.

Or you could tap threads in a piece of tube, say brass, tin it, and
then cast the lead around it.  I've definitely seen this done for
counterweights on lab instruments.  Aluminum might work, too.  Steel
and C.I. will work.  Thread the inside of a black iron (not galvanized
[zinc]) pipe nipple.

Before anyone asks -- old car batteries are not a source of lead,
unless you have a professional smelting shop.  They're alloyed with
cadmium and that's toxic and doesn't cast right anyway, and you can't
refine it at home, although I hope Mr Schwartz can prove me wrong :-),
as he takes the word "can't" as a personal challenge.

Wheelweights are of two kinds, alloyed with tin (good) and zinc (bad).
Zinc leads to bad castings.  The zinc ones are the shiny ones.  One
bad one spoils the melt, I'm told.  whether this means it spoils it
for a counterweight, I don't know, but it is definitely bad for bullets,
which are more critical in shape and hidden voids.

Or one can buy chilled lead shot or cast bullets (or pre-alloyed
ingots of casting alloy) at a gun store, this stuff is not particularly
expensive, since most of the guys who use it are skinflints.  Hmmm,
you could cast the shot in epoxy or plaster or concrete.  Fishing
sinkers are another source, but they're usually dead soft. (Pure
lead).

Dave

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