I need to figure out a way to punch out shapes from .025 aluminum sheet.
I've got the little taig mill of course, but I'm thinking it will be
incredibley slow, and if the project works I'll want to punch a lot of them.
The shape is roughly triangular with an outside shear length of
approximately 6 inches.
I also considered the idea of making some kind of punch that I could use in
my press, but I haven't any idea how to start or what material to use for
the punch itself. Also, I am thinking something as slow as a hydraulic
press is going to tear and distort the metal rather than punch it out. I
made a couple of custom punches out of some stainless rod stock for another
project a while back and even for paper they only lasted a very short time.
Going back to the idea of using the mill. What do you think is the most
aggressive cut and cutter I could use? The spindle RPM maxes at 10,000 and
my max IPM is about 30 for rapids, but with any force for feeding is 20. I
have a couple details on the cut that could double as holding tabs and be
cut as a seperate operation.
Stack up a bunch of blanks and chew them all out at once. Could also
do the same and use a pin router with a template on top or bottom.
Usually uses handfeeding against the guide pin. Quite common to use
wood-cutting router bits on aluminum, too.
Consider a Beverly shear to cut them out. You didn't say how much "a
lot of them" is, but a Beverly shear can cut them out pretty fast. This
kind of shear cuts around curves, too. Harbor Freight has a knock-off
model for something around $100 that would work well for this. I have
had one for several years and it's one of the neatest tools in my shop.
If you lived around Baldwin Wisconsin, I'd be glad to let you try it out.
Bob La L> I need to figure out a way to punch out shapes from .025 aluminum sheet.
Well, I just have a generic open frame 12 ton air over hydraulic H-frame,
but I was thinking something like a compound lever action arbor press might
work better if it will produce enough force.
I'll have to look see what O-1 is. If it machines well I guess I could just
make it with my little mill easily enough.
Hmmm.... that is an option.
Initially maybe 100 or so. Give or take. They need to be pretty identical
though and have exactly the same weight.
Watch it. That's the kind of thing that's likely to get me to roll the bike
out of the garage.
Hmm ... for distortion -- make the punch nose flat, and the die
angled so it starts cutting near the middle of one side and at the point
opposite (assuming that the triangle is equilateral) so the distortion
is in the waste stock instead of the workpiece. (This probably means
that you want to shear to blanks not too much oversized to start with.)
Hmm ... this sounds like a job for a flywheel punch press. But
with a 6" perimeter, my little 1-1/4 ton one would not have a chance.
O.K. A bit of calculation, with a full perimeter of 6", a
thickness of 0.025" and 6061-T6 aluminum at 30,000 PSI shear strength
gives 2.25 tons using the formula:
and replacing the Pi*D with your 6" perimeter.
Here is a 7-1/2 ton one on eBay if you are near New Jersey:
And a 10 ton one:
And a 5 ton one:
Search for "punch press"
These essentially have a flywheel spinning around a shaft with
an eccentric which drives the punch holder a short distance. There is a
dog clutch which is tripped by some mechanism or other (some are air,
other mechanical) after which there is a quick up-and-down stroke and
then the clutch releases and pauses for the next trip.
Note that these strokes are quick and thus quite dangerous to
the user. Probably best if you set it up so both hands are required to
Which stainless? They are not what I would choose for a punch
anway. And paper has clay in it, so it is rather abrasive compared to
I would use a high carbon steel (and did -- D2 air hardening --
to make some punches to cut out circles). Machine it to near the
desired shape, harden and temper it, and then grind it to final
And make sure that there are guide pins to keep the punch and
And add a stripper to pull the workpiece off of the punch on the
Part of the problem is that you need a way to pull the chips out
as the workpiece is cut. Since you are cutting through, put some
sacrificial material below it. Use a shop vac with a reduced nozzle to
pull air quickly past the cutter.
Perhaps have a toggle clamp which you can swing into place after
the cutter passes so you don't need the tabs.
But if you want quick -- you are really talking about a punch
press job here.
Or perhaps a waterjet cutter with a stack of plates to perhaps
1" thick or so (depending on precision needed) so you make a lot of them
in one machine pass. (This means contracting it out, of course.)
FWIW -- the 1 ton punch press (or is it 1-1/4 Ton?) that I have
I can just barely carry from one horizontal surface to another not too
far away. Anything bigger -- expect to use something to help lift it.
FWIW, the recommendations to make punch and die sets for this job seem a
little cavalier. The punch/die clearance will be rather small and difficult
to keep consistent with a manual mill, unless one is very good and has the
Tawwwwwm mentioned O1, which would do it easily for a few hundred parts, but
heating a die of that size with a torch, as he recommends, sounds like a
disaster waiting to happen. O1 is forgiving but this is an inside shape, fer
chrissakes. I wouldn't try it without a decent heat-treating furnace.
D2 is overkill. It would work fine, but you're making the job more difficult
than it has to be.
If I had to do it (and I wouldn't -- I'd have it wirecut; I think the
clearance is enough that you can do a one-shot punch/die set from a single
piece of steel) I'd make it from a free-machining grade made for case
hardening and have it case hardened by a heat treating service. The cost is
modest and it beats the heck out of doing a high-wire act with a torch.
As for curving the die set (cutting "shear" into the die, if the saved piece
is the inside piece of the punching) to reduce forces, it's not a bad idea
if you really have to. But if you can't develop 2.5 tons of force with your
press, you have another problem. A press lighter than that is likely to
strain, trying to keep the die centered in the punch. You'd need guide pins.
Building a punch and die with guide pins and bushings is not for tyros. And
don't forget to file some clearance into the die -- or make it thin, and
make a die shoe with a slightly larger hole.
This is not a trivial job. If the stock was 0.006", it *could* be trivial.
[ ... ]
O-1 is a high carbon oil hardening tool steel. You heat it up
until it no longer attracts a magnet, then quench it in oil. Then, if
you don't want it to be too hard and brittle, heat it up again, to a
temperature determined by what hardness you want. I would suggest about
Rockwell C 59 to 61 as being reasonable. From the tables in:
you heat it to about 475 F (should be able to do it in the kitchen oven,
if SWMBO does not object).
They suggest an hour per inch of thickness to get the tempering
done all the way through.
Since you want a precise clearance between punch and die, and
since the steel expands slightly when hardened -- you want to make it
with overlap between the punch and die, and after hardening, use a die
grinder to adjust to the desired final dimensions.
Make the hole too small, because it will grow with the material
surrounding it. Make the punch just slightly too big to give room to
grind back to a clean surface.
BTW You want the hole in the die to be the right size at the surface,
and to taper larger behind the surface, so you don't wind up
with the slugs getting stuck in the dies. (Especially here,
where the slug is what you actually want to make. :-)
I *think* (but you should verify this first) that the usual
clearance angle in the die is 7 degrees.
Almost all my O-1 dies are full hard with no tempering. I counterbore the
dies rather than taper, I leave 1/4" of land. Usually, I machine to size
and not grind to size. O-1 doesn't move that much for me. But, 95% of my
dies are for round parts in 19-11 ga. mild steel.
Wow! It doesn't have to be that complicated. I have O-1 dies, full hard
with a torch and a bucket of quenching oil, that have served for decades
making many hundreds of thousands if not millions of steel parts. A lot of
them are on shoe plates not die sets unless there is more than one
operation. But, I've made hundreds of die parts and have a knack for
machining and heat treating them trouble free. OTOH, I've had some give me
real headaches. For most of the high production or complex parts, the dies
and punches are D-2 on die sets professionally heat treated. The OP job
isn't above the hobby category, it can be way less complicated than a real
I mentioned to a friend recently that the dishwasher would be a good
way to clean some copper parts prior to patination. The alkali nature of
the wash agent being good at removing finger prints etc. Apparently that
and the patination worked a treat although she said her husband did give
her a few odd looks when he saw the stuff in the dishwasher, it didn't
Weeeeeelll.... I think I'm gonna give punch making a try again. I got to
thinking about it and its not much different than using a slug buster. A
tool of which I have a couple. One hydraulic and one manual. The key being
I'll have to design my irregular shape slug buster to use a c-clamp type
configuration instead of a bolt through configuration.