machining top punch

porthos

Active Member
getting ready to make some bump dies. got everything figured out,except. how am i going to cut the nose in the top punch that is going to form the new nose shape that will swage the bullet under pressure. i'm worried about leaving a ring around the nose after bumping. and, i would like to continue to have a spitzer style nose. any help??
 

Pistolero

Well-Known Member
Cut an oversized cavity and use a filled epoxy like an "epoxy steel" to make an
exactly matching cavity in the top punch, by molding it to the bullet, in place in the
die, so that it will be aligned correctly. The strength, when fully surrounded by
a steel punch body, and loaded in compression will be fine. Use some paste wax
for mold release on the bullet nose, a couple of coats.
 
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porthos

Active Member
thanks; i've always used epoxy to form top punches. but in this case i thought that it might not hold up under the pressure of bumping a bullet. i've always used acra-glass jell with ss powder.
 

Ian

Notorious member
Metal-filled Acra-Glas should be fine. I prefer Devcon liquid steel or Marine Tex grey.

You could be stubborn like me and grind a form tool to match the nose profile via a 10x optical comparator and then cut the nose profile in the end of the drill-rod punch; you get to have razor-edged yet strong sides that way :) The other caveat of the epoxy is you need to make sure your "form" for the bullet nose doesn't have parting lines or isn't elliptical....otherwise you know what.
 

Ian

Notorious member
Here's an ejector punch I made for a TC bullet nose:

20181004_223116.jpg

No picture handy but I did make one for a spitzer recently and it works well and can take a tremendous amount of swaging force while barely putting any marks on the bullet.
 
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Pistolero

Well-Known Member
You may manage to mess up ordinary epoxy, but with a heavily metal filled, the compressive
strength should work. The powdered metal additive versions are very strong in compressive
stress.
Yes, you may want to sculpt off any parting lines for your forming bullet, as Ian said, otherwise
you'll likely be adding parting line marks to them. A bit of 400 grit sandpaper judiciously applied
should do it nicely.
 
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Ian

Notorious member
It's not as difficult as you might think with some good HSS stock and an optical comparator.
 

Pistolero

Well-Known Member
And doesn't everybody have an optical comparitor on their workbench?:):rolleyes:
I have a friend who has one that I could borrow, I imagine.
And sometimes I do get a wild hair to just do something to see what it is like.

Bill
 

Pistolero

Well-Known Member
Here you go, Brad. High precision shadow projector with accurate scales for measureing parts.
Very cool chit. Very expensive new, MAYBE available on an auction from a machine shop going
out of business for a good price. Kinda a precision projection microscope with the lenses
and distances fixed to get accurate measurements on the screen scales. You can't see but there
are scales etched on the screen and you can move the part around on the stage with knobs, very
precisely to line up reference edges with the lines on the screen scale to measure stuff. Different
magnifications are available, often, and all are magnified so you can see much better what is
being measured.

9765

I have no idea what Ian has there, but it looks interesting,hope he will share more info.
 
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Ian

Notorious member
What I have there is also called an optical comparator, but a smaller version more suited to toolbox drawers and much better than the pocket versions. It has all nine standard reticles and 360⁰ illumination built in.
 

Ian

Notorious member
Santa Claus brought the one in the photo last year, it has been invaluable for grinding drill points and especially for getting the angles and root width precise on HSS single-point threading tools. I can now tell you exactly what back angle I ground on my general cutting tools too.
 

Pistolero

Well-Known Member
Nothing like being able to see it well, and at the same time have angular and linear scales
to check it against.
I've tried to explain to people that trigger jobs aren't too hard, IF YOU CAN SEE WHAT YOU
ARE DOING. I use 3X and 10X jeweler's loupes and a headband type of 10X magnifier to
do trigger jobs. When you see what you are doing, it is a whole lot easier to get it right. :)
 
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