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Tight pancake dies for thin materials


#1

One of the many issues not covered in any detail with the original R=
T Stamping System kit ‘instructions’, or in the Rio Grande video I
helped with (many moons ago!), are the requirements to get the
process to work well on very-thin materials. The dies have to be made
tight, very tight, sometimes extremely tight, often tighter than is
desired for speed of use, but sometimes you have to accept this as
coming with the territory. When the alternatives are material jamming
in the dies, or die failure, or simply burrs on the parts, tight dies
are always preferrable.

The obvious adjustment to a normal table-angle setting (and sawblade=
-size combination, which is always part of the equation, along with
steel thickness) is to increase that angle, but another important
thing is heat treating. The greater sawing angle is such that the die
starts out at less than zero clearance between the cutting edges, and
when the die is being broken in after heat treating, the first
closure of the die she ars off a hairline sliver of steel as the
cutting edges contact and move through each other. This shearing
creates a true zero-clearance that facilitates the cutting of thin
material, and also creates a small section -the tips of the cutting
edges where they contact each other- where the angle of the cutting
edges is closer to perpendicular, as with a normal shear, or a pair
of scissors, or metal shears. Non-heat-treated steel does not react
well to the extreme tightness, either in opening the die for the
first time, or closing it. If there is any complexity in the design
it’s easy to bend part of the die with the force required to open it,
and if there is much complexity it can become an untenable situation,
where you simply wouldn’t be able to get the die open without ruining
it. When a tight, untreated die is closed for the first time, the
steel does not allow for the same degree of tightness as a treated
die, because it doesn’t withstand as much shear force directed at the
cutting edges. You could back the angle off a hair, and make a
reasonably tight die, untreated, but you wouldn’t be able to go to
the extreme you could with treated steel. One more reason treating is
important is because untreated dies stretch out and become loose much
quicker than treated dies. Yes, heat treated dies can stretch, unless
they are tempered harder than I usually temper them.

It took a few years to see that most dies aren’t used enough to have
to worry about wearing the cutting edges out, which means that I can
get away with a softer temper than I started out with at first, to
lessen the chance of dies breaking from being harder and more
brittle.

It’s nice to use dies that pop back open by themselves each time
after a punch, but with thinner than about 26 g (24 with softer
metal) it just isn’t practical. Many of you are no doubt familiar
with parts that come out with a burr or lip, and probably have dies
that have jammed, and this only happens because there is a loose
spot (if a die becomes misaligned (for the same reason it stretches)
it will be loose on one side ), or the die is just not tight enough,
either from stretching or from starting out that way. New customers
often ask me if the dies cut clea= nly and I always say that yes,
they do, as long as they start out tight and stay aligned. It can be
tricky to get dies as tight as they need to be for certain thin
materials, paper, acetate sheet, steel used for tins, etc., and with
complex shapes, it can be almost impossible. Almost, but people want
what they want, so I figure out how to make the dies work as well as
they possibly can, because I have to, and most of the time I can. Not
that I haven’t been defeated… I had my rear end handed to me by
some stainless steel foil, and thicker stainless steel more than
once, and of courese some designs are just impossible. One die I
just made took about ten minutes to open up the first time,
carefully tap= ping it open bit by bit from the back with a small
punch, and closing it each time to do that shearing thing gradually
instead of all at once.

This can be especially dicey because it’s easy for a complex design
to open unevenly, which misaligns the edges in places, and closing
misaligned, tight dies in this situation can be disastrous. This
parti= cular die was of a square rosette shape, with four squared
petals separated by four long, narrow spaces between each petal. Two
inch diameter shape, with 3/32" wide separations extending about
3/4" inwards towards the center. The more complex a shape is, the
harder it is to get open the first time (speaking of tightly-made
dies as we are, here), and with this design being intended for use
with 30g galvanized steel sheet, it needed to be extra tight. It was
impossible to just knock it all open at once, because the
negative-space pieces would’ve bent badly or snapped off, so it was
tap-tap-tap close, tap-tap-tap close, little by little. I can’t open
it with my hands, and it doesn’t open by smacking it on the table,
like most moderately-tight dies, but I know because I’ve been making
dies like this for this person for twenty years, that it has to be
done this way.

I should also note that this sort of opening needs to be done after
tempering, which is second nature, no-brainer info to me, but
obviously not as obvious to everyone else. Case in point, one guy for
whom I sawed out a die with two little horses on it. Tightly sawed
little horses they were, and since he has made his own dies , he heat
treated it himself, and as he does, he tried to open it after
quenching it, but before he tempered it. This guy gave me the idea of
heating the hinges in the open position to lock them in that
semi-open position, which makes them much easier to load metal into,
but his method was to do this as part of the tempering stage of heat
treating. So, he went to open the horses up before the die was
tempered,right after it was quenched, and therefore the steel was
very hard and very brittle. Since the die was tight and the steel was
brittle, he broke it. My way being second nature to me, I hadn’t
thought of explaining the need to temper it first. This is extreme
diemaking, right at the edge of what can be done, and sometimes over
the edge, and I’ve found out where a lot of those edges are by
stumbling over them and falling off, but that’s a small price to pay
for the satisfaction that comes with doing something like this out
here on the (bad pun time) ahem, ‘cutting edge’ of what can be
achieved with the process.

Dar Shelton
the sheltech guy
www.sheltech.net
www.soundclick.com/darshelton