Eccentric Hoop Punch Guides, Done Two Ways

If you make jewelry out of sheet metal (or for that matter felt, plastic sheet, leather, maybe cardboard?), 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.

This Instructable shows two (or three) ways of making what I call "hoop eccentricizers," depending on your tools:

1. Using dowels, a drill, and some sort of vise - a simple method and a slightly more involved way.
2. 3D printing using a parameterized model I made.

Both versions work pretty much the same way, and for context, I'll show how the tools are used before showing how to make them.

In general you will need (and probably already have) a set of disc punches, and an arbor press or heavy mallet to drive it, and the materials you want to punch. In addition, for the eccentricizers you will need either:

1) For the simple, wood method:

• Dowel of each size punch you will be using for the outer discs, plus a much smaller dowel or metal rod.
• A saw to cut it (a miter saw, hand powered or electric, is ideal). If your peg will be metal, a hacksaw to cut that.
• Coarse sandpaper
• A drill or drill press
• A vise to hold it while drilling
• A drill bit the size of the much smaller dowel or rod - a Forstner bit is great, but any will do.
• Wood glue
• ruler and pencil
• (optional) center finding tool
• (optional) drill guide (if you don't have a drill press)

1a) For the fancier wood method, you'll need all of the above, plus

• Dowels of all the inner hole sizes
• Drill bits (again, ideally Forstner) of all the inner hole sizes

2) For 3D printing (see step 7):

• Access to a 3D printer (FDM is probably better for this than resin printers)
• Filament (I used PLA and PETG)
• 3D models available here.
• (optional) Fusion 360 to alter the parameters to create exactly the size and proportions you need.

Before showing you how to build the hoop eccentricizers, it's worth understanding how to use them. I will assume you know how to use your disc punches in your chosen material.

Purpose:

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.

See the two attached short video clips. Hopefully I will be able to make a longer video to post on my YouTube channel soon.

The simplest way to make a hoop eccentricizer is with a dowel stuck in the end of a larger dowel.

Considerations:

• You will need the larger dowel to be as close as possible to the size of the top hole in your disc cutting die. However, if the dowels you find are a little small (the 1" dowels from my hardware store weren't really 1", for example), you can wrap a few windings of masking tape. This fitting should be done first, before measuring and marking for the hole for the smaller dowel.
• The smaller dowel needs to be smaller than the smallest hole you want in a given size hoop, but should be as close to that smallest hole size as possible. The closer the peg is to the size of the hoop hole, the easier it is to get everything lined up the same way every time.
• If you have the tools and can get the material, making the peg out of metal such as aluminum or brass would make it much more durable in use.

Preparation:

1. Decide the size(s) of hoops you're going to make, and make sure you have dowels of each outer diameter. The one shown is 1" diameter. You can make all the pegs the same size, or make them different sizes for each eccentricizer. The peg for each eccentricizer needs to be a little smaller than the smallest hole size you plan for that size hoop.
2. For each eccentricizer, decide the width of the narrowest part of the hoop it will make. This will determine where you put your peg.

1. Cut your large dowel to length. It needs to be as long as the upper section of the disc cutting die, plus enough to hold onto conveniently (1/2" - 1" is about right for the latter). It is very helpful to cut this in a miter box so that the cut is square. If not, work to make it as square as you can on at least one end with careful sanding afterwards.
2. Clean up the cuts with light sanding.
3. If your dowel is a little too small, wrap it with a few layers of masking tape near the good end.
4. Measure to drill for the peg.
5. On the good (square) end of the large dowel, mark a center line across the dowel, using a center finder, or a compass, or careful measurement.
6. Measure along the line from one end.
7. You can mark the center for drilling, by measuring the narrow hoop width, plus half the diameter of the peg you're going to use.
8. OR, if you are using a Forstner bit for the peg hole, you just measure the narrow hoop width along the line, then place the edge of the bit there, and push its center in to mark the drill point farther along the line. If you do this, I strongly recommend doing it lightly first, and spinning the Forstner bit by hand to scribe out its circumference, in order to check that the bit is really centered on the line.

Bonus extra tool how-to!

It is important to drill the hole in the large dowel as straight as possible. Ideally, you can do this in a drill press. But that still means you need to hold the large dowel very straight in a vise on the drill press. If you have a drill press vise with a wide vertical channel in the jaws to hold dowels vertically, you're fine. If not, you can make a simple jig for any size dowel. I used a scrap of 2"x2" wood for this.

1. Draw a center line along a bit of the wood.
2. Clamp the wood in the vise, and drilling a hole through it of the size of the dowel you wish to clamp, centered on the center line. It's important to get this hole quite straight.
3. Take it out of the vise, cut off the bit of wood with the hole in it, then cut it in half carefully along the cut line. I used a thin Japanese saw for this, but in this case, a wider kerf is actually better.
4. You can now use the two halves of this piece to grip the dowel quite solidly in your vise.

1. Clamp your large dowel and drill the smaller hole in it for your peg. It should be at least 3/8" (1cm) deep to hold in well, but doesn't need to be much deeper than that.
2. Cut your small dowel or rod for the peg. It only needs to protrude by 1/4" to 1/2" (5-12mm) from the end, so cut it to suit.
3. Clean up any cutting burrs on the peg, and lightly chamfer the end with sandpaper on a board, or with files. A slight taper just on the end of the piece makes it easier to use. The taper should not be long enough that it is still tapering where it enters the large dowel.
4. Glue up the un-tapered end with a little wood glue, and insert it into the hole in the dowel. If there is any play in the peg, try to get it to end up straight up, but if it has to tilt, make sure it tilts toward the center of the dowel - along the drawn center-line, that is.
5. Let it dry, and move onto the next one you're going to make.You're ready to make some hoops!

Instead of making one eccentricizer for each outer hoop diameter, if you want to spend the time and materials, you can make one eccentricizer for each finished hoop configuration. That is, for each combination of outer hoop size, inner hole, and minimum hoop width. This will make for very positive fitting and very consistent results, and probably less wear and tear on the pegs. But it takes having dowels and drill bits of all the inner hole sizes as well as outer hoop sizes.It would be a great array of tools at the end, though.

The technique is the same as for the simple dowel version. But it will take a while.

(There's also what I might call Option 1b, of course. If you have a lathe and the skills needed, and a 4-jaw chuck, you could also turn the eccentricizer on the lathe as a single piece, either in hardwood or in metal. But I'll leave the working out to you if you have the skills and patience.)

So if you skipped down here after the intro, welcome!

This is what I use in my studio, and my original idea when I first started making my hoop earrings in patinaed brass and copper.

On the Printables page you can download STLs for several sizes of hoop eccentricizer in US standard units, from 3/4" to 2" (19 to 51mm) outside diameters. They all have 1/8" (3.2mm) minimum hoop width, which is enough to punch a 1/16" (1.6mm) hole for the earwire.

With the eccentric cone on top, a single tool can be used for many different sizes of hole, but only one minimum hoop width. Wiggling and twisting the eccentricizer and the sheet will give you a very positive contact and consistent results.

I have printed these in PLA for my own use, and it seems quite durable even against sharply burred copper and brass workpieces. I'm sure PETG would be even better.

Customizing the model:

If you want other sizes, either for metric punches, or for different minimum hoop width, you can alter the parameters in the F3D file using Fusion 360. In Fusion, in the Solid environment, go to Modify>Change Parameters. You can set the largePunchDia (the diameter of the outer hoop), the minHoopWidth (the width of the narrowest point on the hoops you want to make), and the smallPunchMaxDia (the largest hole you intend to make in this size hoop).

If your punch is a little smaller than nominal, or your printer makes things a little too big to fit, you can set the parameter ease to subtract a little from the outer diameter.

You can also vary the total height of the barrel of the eccentricizer, which is upperDieThickness+gripHeight. If for some reason you need to change the shape of the tapered cone, it depends on the smallest size inner punch you intend to use (smallPunchMaxDia) and the height parameter (coneHeight).

Note: you may use these 3D models to print eccentricizers for your own use, and of course use them to make earrings or other parts for sale, but you may not sell these 3D prints themselves.

Happy making!