Eccentric hoop punch guide (Hoop Eccentricizer)

For more information, see my Instructable on using these (and on making a simpler non-3DP version). 

If you make jewelry out of sheet metal, you probably have a set of graduated disc punches. At some point, you may realize you want to make a ring-shaped cutout, called an annulus. If you're using a standard set of straight punches and dies, either in a press or with a mallet, you can pretty easily find standard-sized centering tools to make a concentric annulus, like a washer. But what if you want to make the inner hole off-center on the disc? You can do it by eye, but if you want more precision - say, for a matched pair of earrings - you need a different system. These provide that system. 

Jewelers often use disc punch sets to create not just discs, but annulus (ring) shapes. There are widely available tools to help you center the hole on the outer ring. But if you want to make the hole off center (eccentric) on the ring or hoop, rather than centered (concentric), there is no system to make the positioning consistent. I wanted to make matched pairs of earrings in this eccentric hoop shape, so I devised a way to position the outer die consistently so that the hoops match, and have just enough space on the narrowest part of the hoop to punch holes for the earwires.

Note: Each eccentricizer is defined by its outer diameter (the outer diameter of the hoop) and the width of the narrowest point of the hoop. Every hoop it makes will have the same width at its narrow point, if you're using it correctly.

How to make Eccentric Hoops:

1. Punch the interior hole, leaving space around it for the hoop itself. If your material, like my patinaed brass, has a front and a back, I recommend punching the inner hole front-to-back so that the cutting burrs on the final hoop both face the back.
2. Flip the sheet and place it in the die with the inner hole near where it should be.
3. Insert the eccentricizer so that its peg or conical protrusion goes through the hole in the sheet.
4. Wiggle the eccentricizer and sheet around until it is properly seated, pulling the sheet against the protrusion.
5. If you are using the 3D printed version, seating the cone as far down as it will go should position the hole properly to leave the right size narrow portion automatically.
6. If you are using the wood dowel version in its simplest form, you will need to do it by feel, rotating the eccentricizer and pulling away from it, to make sure you have made the narrow part of the hoop as narrow as possible (and thus consistent from one to the next).
7. Carefully holding the sheet in place with respect to the die, remove the eccentricizer, and make sure it looks like you got the hole in the right place.
8. Continuing to carefully hold the sheet in place, insert the punch and punch the hoop.
9. If you are hanging the hoops from the narrowest point and want them to match, you can use the eccentricizers to mark the spot you want to punch a hanging hole, by placing the hoop over the eccentricizer, and centering it by feel, which will place the eccentricizer's protrusion just at the thinnest point, and you can mark that point, then center-punch it and drill or punch your hanging holes.

The parameterized .f3d file lets you alter the outer diameter, the “ease” (which is subtracted from the outer diameter, in case your printer prints a little large or your punches are a little smaller than nominal), the maximum size of hole you intend to have in a given size of hoop, and the minimum width of the hoop.

The individual .stl files are sized for common US standard punch sizes from ¾" to 2", with a minimum hoop width of 1/8" in all cases.

I'll work on providing a metric-native set soon.