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Hardened tool steel for pancake dies


#1

Because the original RT Blanking System came with type 0-1 flat stock
(oil hardening tool steel) and I had a small electric kiln at the
time, I began my diemaking adventures with the goal of maikng the
best tools I could practically make, and one of the important aspects
is proper hardening, or heat-treating. Commonly mis-identified on tv
programs about the manufacturing industry, heat treating, in the case
of 0-1 dies like these, is a two-part process : 1) hardening, which
is done by heating to 1500 F and quenching in oil, and 2)
tempering/drawing, which is done by reheating to a specified lower
temperature (roughly 600 F to 900 F, depending on design and
application) to decrease brittleness and increase toughness.

Not all jewelry applications require heat-treated tool s= teel
(HTTS), or even tool steel, but again, I started and continued
making HTTS dies because they perform best, and are definitely
required for many jewelry applications. The difference in toughness
between mild steel or unhardened tool steel is obvious and huge;
just think of the difference between a hammer and a piece of iron :
the hammer always wins and always remains intact because it is
tough, and rigid, but not too brittle. It’s the same with pancake
dies, they need to be tough, and largely rigid, but since they flex,
and are fragile due to their relative thinness, they need some
spring, and generally should not be made quite as hard as a hammer,
and some need to be significantly softer.

Certain designs, like a spiral that winds around in on itself, or a
small hand with articulated fingers, or small animals, present a
dilemma that was only resolved by breaking a lot of dies, and having
a lot deform, over the years until I figured just what I could get
away with and what I couldn’t, as far as design, and heat treating.
To cut such delicate designs, especially in thicker or tougher
metals, the die obviously needs to beas strong and tough as
possible, so that the weak areas (or sharp points) do not deform,
bend, and ultimately fail. However, if you temper a die extra tough
(550-600 F) to cut, say, 20 ga 14ky sheet, it will be too brittle,
and the fingers will break off or the hinge will snap where it hits
the design, or the outer part of the die might even crack. One way
to compensate is to use thicker steel, which makes sawing the die
more difficult, and the other way is to compromise, and temper it
hotter (750-850F) so that it’s less brittle.

Half- hard (or softer) copper, silver, brass, and alumin= um are
generally very nice to dies, and you can make fairly intricate,
small designs for cutting up to around 18 ga, and expect dies to
last for hundreds, if not thousands of cuts, tens of thousands,
even. The other part of this equation, and why deciding exactly how
to temper dies can be tricky, is that because you want to temper a
delicate-design die softer, to lower the risk of breaking, you run
into the possibility of making it so soft that it will not be tough
enough to withstand the intense forces directed to small areas. You
may make it so soft that it will bend and not flex back. Permanently
bent spots on dies are an obvious problem because it’s clear that
the application is more than the die can effectively deal with, and
it will fail eventually. Such bending can cause immediate
misalignment, which is an immediate problem which shows up as
ragged-edged parts or metal sticking in the die.

Situations like this are something of a gray area though, because
they are by default compromises. You can’t have it both ways: with
certain designs, you can’t make the die as tough and hard as you may
want, nor can you make it as soft and unbreakable as you may want,
and a certain percentage of dies will either break or deform and
fail. In production runs, with tough applications and vulnerable
designs, this just comes with the territory. Heat treated tool steel
is an incredibly strong material though, and I’m often still amazed
at how well some dies hold up to sometimes very brutal jobs.

One more common occurence with unhardened and non-tool-s= teel dies
is stretching, when the whole outer part of the die expands slightly
with repeated use, which causes the tolerance between the cutting
edges to relax and become looser. This shows up as parts with slight
rims, or burrs, or metal sticking. This even happens to heat treated
dies that get a lot of use ; since the dies are softer than a
hammer, they are slightly bendable. The original RT setup came with
1/32" tool steel, and while that isok in my opinion for minimal use,
I never use it for dies I sell because it has always seemed too
insubstantial to me. Even when heat treated, it’s thin enough to
flex excessively, and that can allow thin metals to stick, among
other things. Unhardened, it’s susceptible to premature bending and
stretching, and general failure because it’s so weak, and since 0-1
gets more and more expensive as it gets thinner, I just don’t use
it.

Another important consideration involving die thickness is the angle
at which dies are cut at; the degree to which the saw table is tilted
to get the tolerance correct for a given steel thickness and
sawblade size. Much can, and eventually will, be written about this
specific area, but the basics can be covered briefly. The thinner
the steel, the more actute the sawing angle needs to be, and the
weaker the resulting cutting edge will be, so the thicker the steel
is, the steeper the angle and the stronger the cutting edge will be.
Then, the bigger the sawblade is, the more actute the angle needs to
be, and smaller blades call for steeper angles. Where more-acute
angles are problematic is in delicate areas, thin areas, and points.
This is because the acute-angled cutting edges are weaker than
steeper ones, and the cross-section of these areas shows that there
is less mass to give strength to these areas.

Again, using thicker steel will add more and more strength to dies,
and with mild or cold-rolled steel, using thick steel like 1/16" or
3/32" isn’t all that difficult, nowhere near as hard to saw as tool
steel. Coming around full circle, many designs really need to be
made from hardened tool steel.

Dar Shelton
www.sheltech.net