Subject: Re: Volumetric sheet metal work

From: [email-masked] (Andrew Vida-Szucs)
Date: Tue, 8 Mar 1994 17:58:11 GMT

Bill Hubbard <[email-masked]> writes:

> I was wondering if you could use successively deeper concrete (ie easy to
> make) formers to just pound the sheet metal into shape, with annealling
> between stages.  

	You *could*, but it would not work too well.  Look at the surfaces 
	of cold forming dies and what do you see?  SMOOTH surfaces.  Without
	smooth surfaces, the die will bite into the surface of the blank
	and cause the plastic deformation to become extreme in localized
	areas.  One result of this will almost certainly be an unacceptable
	variance in thickness of the work.  In extreme cases, the work may
	tear.  At the very least, you will wind up with work that has an
	extremely ratty, marred surface.

>I understand it would stretch thinner at the points of
> most stress and wondered if you could get away with using successively
> *sharper* curves to get the right shape.  Would this approach be worth
> trying? 

	I don't think so.  Anyone know different?

> Incidentally, various museum and armour experts have assured me that in
> the fifteenth/sixteenth centuries, armour was beaten out and drawn up
> cold and annealed between stages.  Evidence for this comes from
> illustrations of the time.  Too skillfull for me.

	How did you *think* they did it, if not this way?

	-Andy V.

---

From: Bill Hubbard <[email-masked]>
Date: Thu, 10 Mar 1994 15:55:32 GMT

In article <[email-masked]> [email-masked]
(Andrew Vida-Szucs) wrote:
>	of cold forming dies and what do you see?  SMOOTH surfaces. 
 
Thanks for the information:  I have never seen cold-forming dies, so did
not know that they had to be so smooth.

>	How did you *think* they did it, if not this way?

I thought that armourers would have worked the metal while it was hot and
therefore more malleable, at least to the form of a basic shell, before
just finishing off cold and work-hardening it. The evidence for them
working it cold throughout was what surprised me.

---

From: [email-masked] (Rick Cavasin)
Date: 10 Mar 1994 19:00:24 GMT

In article <[email-masked]>, Bill Hubbard <[email-masked]> writes:

(snip)...

|> I thought that armourers would have worked the metal while it was hot and
|> therefore more malleable, at least to the form of a basic shell, before
|> just finishing off cold and work-hardening it. The evidence for them
|> working it cold throughout was what surprised me.

But the basic forming is the easy part (especially with the iron/steel
they had back then).  I'm not sure that work-hardening would make that
big a difference, but they did case-harden armour sometimes.
If you've done much work of this sort, you can see pretty quickly why
hot forming is largely impractical.
Once the iron is beaten into plate, it's surface area/volume
ratio is pretty high, and it won't stay hot long enough to get much work done.
You loose alot of heat transfering the piece from the forge/furnace to the
work area, and then your anvil/stake will suck away the heat even faster
when you start to work it.  Added to that, you have the problems with changing
your grip with the tongs (eg, while rotating a spherical piece on a round stake).
The scale built up by constant heating could also be a problem.
With the right tools, knowledge, and skill, you really can do alot.  It takes
some time to get the feel of it, and to get good at knowing how to hit the
metal to make it go where you want it (NOT that I'm an expert!!).
Books on silversmithing/goldsmithing can be very handy.  Many of the same
principles apply, the tools are just bigger for armouring.

Cheers, Rick C.

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From: [email-masked]
Date: Tue, 15 Mar 94 23:32:18 -0500

>	How did you *think* they did it, if not this way?
 
It can be done cold if the metal is soft to start with and relatively
thick (12-8 Ga).  You will have to anneal it once the major sink has been
done before its taken to a stakes for working the edges back inward for a
tighter nape.  A lot of the cheaper; ie common soliders, helms were made
in halves and hammer welded in a forge or even riveted with sunken rivets.
  The real key is in the style of hammer and the manner in which you work
the process.

---

From: [email-masked]
Date: Mon, 21 Mar 94 00:20:29 -0500

RICHARD ALLAN JOHNSON <[email-masked]> writes:
 
>	This sounds like you are describing a dishing process.  I beleive 
>that the first fellow is reffering to raising which is commonly done in 
>silversmithing.
>	The process is to create gooves from the center straight out with 
>the grooves getting deeper toward the edge of the metal circle and then 
>pounding them flat again.  This causes the outside diameter to shrink and 
>casue a bowl shape.  This requires many, many annealings in steel.  Quite 
>the job when you work by yourself.
 
Crimping is a serve pain in heavier gauges.  Spirial sinking from the
edges inward can form a hemispherical bowl in 12GA HR in about 20 minutes.
Of course this implies a heavy hand and a good smooth cupped depression
in which to work.
 
Raising from a flat is equally a pain.  Better to dish the basic form
and then use the raise to pull and refine the final form.