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Old 04-29-2007, 06:45 AM
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KurtB KurtB is offline
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Join Date: Mar 2007
Posts: 192
Default The Coin Collet! Interested?

It appears that coin carving these days is more popular than ever. Steve's excellent tutorial is evidence of this, but holding the little rascal can be tricky. I've seen guys use pitch, hot glue, or any number of tricks to get the coin stable and secure. I thought that perhaps their was a better way! I dug into my closet coin bucket, and gathered a handful of Jefferson nickels, both old and new, as well as some buffalo nickels from my own coin collection. All of my Buffs are fairly worn... they were bought by a young boy (me) a long time ago at coin stores and shows, and I couldn't afford the nicer specimens!

Anyway, a few days ago, I designed and machined a prototype workholding device, and sent some pictures to Steve. He liked the device. I asked him if it would be OK to offer them for sale to the membership here, and he gave me his approval.

My goal was a fixture (I'll call it a CC, for Coin Collet) that would FIRMLY hold a nickel, and present either surface to the engraver, for any operation: roughing, background removal, and finer cuts and shading. The coin can be installed and released in seconds. The nickel's surface is presented above the holder's rim, meaning the CC does not get in the way of the engraving operation. A single 8-32 socket head cap screw secures the coin by collapsing the body of the collet around the rim of the nickel. No set screws touch the nickel, and it is unmarred by the collet.

To achieve this sort of clamping requires an accurate bore (hole) for the nickel. When I put a good micrometer across a dozen nickels, both old and new, I was amazed at the variation in diameter. I don't know if they left the mint this way, but it is significant, on the order of +/- 0.005" from the average diameter. This means I needed to create a double-ended fixture. One end of the fixture will be the large end, the other a bit smaller. Between the two ends, it'll clamp pretty much any nickel out there, short of one run over by a train! You won't need a micrometer to figure out what end to use... start with the small end, and if it seats itself before tightening, use that end. If it won't install, switch to the large end.

These pictures are of the rough and quick prototype, and I do apologize for the quality of the shots. I didn't even finish cleaning up the swarf (small metal chips, etc) from the inside. The finished CC would be clean, and sport a glass bead-blasted exterior finish. I was going to execute a better prototype, and take some nicer shots, but I ran into a bit of a time crunch with work. So I decided to post these, and see what interest there might be in such a fixture.

The round stock is turned, bored through, and then precision bored each end for the two different diameters. It is then split, and drilled and tapped for the set screw.



The CC, plus the modern Jefferson/Buff nickel, are resting on the jaws of my engraver's vise. This gives you an idea on the size of the unit.



Note the double, or stepped, recess in the body of the CC. This step ensures that the CC is holding ONLY the very outer rim portion of the coin. If you have tall engraving, inlays, or an irregular surface, there is no problem, as the surfaces of the coin don't touch the fixture... only the rim and perhaps ten thousandths of the coin faces make contact.



With the nickel installed and secured, it is accurately and securely held in the V-guide of a standard engraver's vise jaw. When removed from the vise, and reinstalled, it returns to exactly the same spot it was earlier. Scope users will appreciate that.

There are refinements that can be made. The CC can be turned and bored from perhaps blued steel for a lifetime of coin workholding. A rim can be left in the outer diameter of the CC body which will register with your vise jaws, meaning the CC can be removed, reinstalled, and it will retain the exact Z-axis relative to your setup. It'll be in focus, and at the correct height. Finally, this system is not limited to nickels. A similar unit can be machined for any sized coin, medallion, or other round object.

I was thinking about making a run of these for the hobo nickel enthusiasts, but before I actually get to work, I was wondering if this was something that would appeal to you coin engravers out there, or if there was some refinement that could be engineered into the device that I, a beginning engraver, might have missed. The price would be somewhere between $20 and $30 for a standard 6061-T6 aluminum double-ended collet. Custom machining or diameters would be reasonably priced, as these are all handmade anyhow, and a different diameter simply means that I must start with larger stock. Sound good? Steve L. gave it a preliminary thumb's up, as he and I both think it would be a useful addition to the coin-carver's arsenal.
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