RE: [CAD_CAM_EDM_DRO] Re: Making a punch die?

Hi again Joseph

These Pioneer brand punches (the small ones) I have were made before zip
codes (I looked at the boxes; give postal zones); I don't recall anodizing
being that popular back then. My Dad had an electronics parts store, and I
worked for him occasionally while in high school (late '50's). They're not
as sharp as a lathe tool or endmill but definitely have a ground edge. I
feel SURE they are heat treated in some way.

Heat treating is something I'd like to learn something about. All I know
about is heating to cherry red and quenching in water. I recall we did
something in metal shop using oil and something else heating the metal in a
chemical in an oven to red hot, but that's all been too many years ago to
remember. Anyone that knows some good references?

Lew

-----Original Message-----
From: Joseph [mailto:toybuilder@...]
Sent: Friday, July 13, 2001 8:58 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Making a punch die?

Thanks Fred.

I sort of expected that the cutting edge had to be sharp and smooth.
When you said that grinding the end is easy, but the sides might be
hard, do you mean the part of the punch that contacts the to-be-
displaced sheet metal (end) and the surface that travels along the
sheared line (side)? Wouldn't having the side relief take care of
the latter?

Hmmm, I just realized that maybe you mean the inner wall of the die
for the "side".

In my case, I'm making these dies for light-duty occasional use on
plain aluminum sheets (and plastic too), so I'm hoping that a little
bit of slop will still be okay.

--- In CAD_CAM_EDM_DRO@y..., "Fred Smith" <imserv@v...> wrote:
> > side cuts through the aluminium. At the very least you would need
> to shape
> > the bottom of the punch so that the cut is progressive i.e. it
> starts at the
> > middle and finishes at the ends or vice versa.
>
> A couple of more comments to help you decide to CNC machine them if
> possible.
>
> Punch/die construction and effectiveness depends on some things
being
> done right.
>
> #1 and absolutely critical is that the punch have a sharp-sharp
> edge. You CANNOT mill this edge. It MUST be a ground edge, or you
> will make snaggletoothed holes. That means that both the sides and
> the end must be ground. Grinding the end is easy, and you just
grind
> two angles to help reduce the force required at any point in time,
as
> posted above. You might even get away with the finish from a disk
> sander. However the sides are another matter. Grinding them is
pretty
> much out of the question for home/hobby equipment. You might get
> away with a milled surface, but should at least polish it smooth
> before heat treating. A steel punch should be heat treated to at
> least 55-60 Rc before grinding. Anything less and if you try to
> punch steel you will have a swedged cutting edge and the punch will
> be useless. Aluminum is very abrasive(many cases are annodized),
and
> it is just as critical to harden the punch and die for aluminum to
> prevent premature wear on the edges.
>
> #2 most punches and dies also have a side relief. This helps
prevent
> the punch and die from becoming jammed together after the punch
> enters the die. It also reduces the chance for a tiny piece of
swarf
> from getting jammed between the two and preventing the removal of
the
> punch. Complex shapes like a D hole or a connector clearance hole
> punch can sometimes be made by precision machining segments and
then
> pressing the finish ground pieces into a retaining pocket or ring.
>
>
> As far as machining them on a CNC machine, remember, you may be
able
> to cut out a rectangular section and screw or pop-rivit a machined
> flat plate into place. It is much easier to cut an Rs-232 hole
into
> a flat piece of 1/16th aluminum, than into the side of a 2x6x8
folded
> box. A hand nibbler will do a nice job of cutting out the large
> hole, and if you have several penetrations for components, they
will
> still be nice and neat, with fairly tight locations.
>
> If you are cutting holes for rectangular components, like switches
or
> power plugs, watch out for the corner radii. Some of them have
> square corners. It might turn out to be easier to mill a small
> chamfer or radius on the component's plastic case, rather than to
> fuss around trying to mill a square corner on a mounting hole.
>
> Been there, done that, what a pain.
>
> Best Regards,
>
> Fred Smith IMService


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