Clever checkmaker

Brad

Benevolent Overlord and site owner
Staff member
I actually just drilled the bottom piece. I think a bored hole would be better as you can control size more precisely and also ensure a round hole.

i formed bottom section first, acts like shell holder in ram. Cut roughly to length. Drill 3/3” then hole. Reverse part and use 3/8” endmill to get flat bottom center hole. Drill to required size for cutting disk. Then mark and cut slot.
 

Brad

Benevolent Overlord and site owner
Staff member
Made a few checks from Al flashing Paul had on hand. Pretty sure it is from Yonoy as it is strips in a coil.
A few have some voids on the edges from not being careful enough in aligning the strip in the slot.
I have a feeling this design is going to be pretty critical of dimensions. Mine is T quite right in relationship between bore of die, diameter of punch, the diameter of cup forming pin, and diameter of forming cavity. Using a drill for size instead of boring is a large cause.
I used a 60° countersink to make the sharp edge for the punch and ease the entrance to the cup forming section. I wonder in a sharper edge, maybe 90-100° would be better for that bevel.
 

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fiver

Well-Known Member
a square 90* cut is what you want.
your punching the disc first and then forming it into a cup.
soo making it 2 separate but smooth steps is best.
think about it like the star lube-sizer one handle press but two distinct steps just performed in one motion.
 

Ian

Notorious member
I think at least a 90⁰ included angle, blended in well on the inside edge, on the inside of the punch would be needed to ease the forming. I also wonder if leaving a very small and fairly sharp teat on the end of the forming mandrel would skewer and hold the disc centered while the punch drew it into a cup.
 
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Brad

Benevolent Overlord and site owner
Staff member
It is that inside forming angle I wonder about. A small, sharp teat might work.
I need to mess with some tolerances on this thing and see what happens. Easy to make another cup forming punch and see what I get.
Material thickness will need to be matched to the die.
 

KeithB

Resident Half Fast Machinist
Wonder if small concentric rings on face of punch might prevent material sliding, less chance of poke through maybe?
 
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Ian

Notorious member
Something else to think about, how about a very slight step to the outside if the punch? Meaning get the tip of it sized for the punch clearance like your daughter explained, and higher up make it just the barest minimum clearance so the upper part of the bottom die (the part above the slit) will more accurately center the punch over the mandrel.

Light lube, annealing the aluminum strips with a torch, and smoothing the inside of the forming punch might be all that's needed to make it wirk to perfection.
 

fiver

Well-Known Member
what... no.
Gary.. don't you go encouraging him to make stuff like that.
 
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fiver

Well-Known Member
i'll put money down on the lopsided checks just being a clearance issue.
I see it with swaging stems if they have more than .001 clearance and sometimes with less than that if it's in contact with flowing lead.
do the math and get things tight and straight, you don't need to lube the sliding parts buut they do need to fit.
 

Brad

Benevolent Overlord and site owner
Staff member
Nothing wrong with the looks of those checks Brad; how do they fit?
Like a frickin glove! They don’t crimp but they slide right on yet are snug.
The spring back of Al makes them not stick as well as copper which bugs me a little. They certainly won’t allow checking before powder coating by tumbling
 

Brad

Benevolent Overlord and site owner
Staff member
i'll put money down on the lopsided checks just being a clearance issue.
I see it with swaging stems if they have more than .001 clearance and sometimes with less than that if it's in contact with flowing lead.
do the math and get things tight and straight, you don't need to lube the sliding parts buut they do need to fit.
And this thing has multiple fits all in one.
The plans uses drills of various sizes for dimensioning and that leads to some pretty liberal tolerances.
 

Ian

Notorious member
Swage dies are also polished to microns.

Annealing the Al might help with spring back.

I don't know what kind of tool Josh used on his but the Al is soft and bites on the bullets quite well if you get them seated good first in a base-first machine with the gas check seating stop installed.
 

Spindrift

Well-Known Member
My experience with home made alu- checks, is they can work remarkably well even if they look like they didn’t get all their vitamins when they grew up. A little asymmetry does little to unbalance the bullet, it seems, when the check is so light. Some of my best groups has been shot with checks looking a little like yours.

When making checks with the Pat Marlin die, I orient the discs with the burred edge facing up in the forming die. The burrs then end up on the inner circumference of the cup, biting into the shank.
 
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KeithB

Resident Half Fast Machinist
Wonder if something like a collet die similar to a Lee crimp die could be used to crimp on checks better. If the GC shank was longer and the check skirt a little taller a good roll crimp could be put on,
 

Ian

Notorious member
Funny you should mention that Keith, I made a rough sketch of a gas check crimping tool that had an adjustable top punch/stop to fit the bullet nose and a flat base punch so the check is first pressed and held firmly against the bullet base and then swaged onto the shank by the collet.