Combined CNC and Hand Engraving on a Hobo Silver Dollar with Handprint Skull


After a few successes with wood, moose antler and brass it’s time for something a little more challenging. There have been a few technical glitches and broken end mills along the way, but I’m confident enough I’ll risk a $20 silver dollar to make a Hobo Nickel…


First, however, I need to come up with a way to hold the silver dollar securely enough that it won’t come loose during milling. That would be a total disaster…so I need to make a special holding fixture, Above, I begin that process by sawing off a suitable bit of aluminum with my trusty Harbor Freight bandsaw…works great as long as you team it up with a good quality bimetal blade… This was about 20 minutes to cut this thick stuff.


Here’s the smaller block, turned out pretty darn square. Looking good so far, but don’t get cocky…


Making an insert to hold silver dollar coins in my CNC mill vise. Here’s the block in the little milling vise, with the dollar laid on top for scale. I’ll mill out a pocket the same size as the coin, but not quite as deep so a little bit of coin will remain sticking out of the top. Then I’ll saw through the center (left to right in this image). The saw kerf should leave enough gap so the vise will close enough for a good grip.


That worked so well I milled a half dollar-sized pocket on the other side. Hare-brained scheme to come, so stay tuned…


Above, I’ve marked the center of the dollar, installed it into the holding fixture and zero’ed everything. It’s now ready for cutting…fingers crossed.


Here, I’ve roughed out everything with a small 1/16th inch diameter square end mill. Still looking good.


Here’s the raw cuts after using a finer 1/16th inch diameter ball nose mill. That looks better but there are still mill marks, and nowhere near good enough for a hand engraved product. I could probably use much smaller steps, but I don’t think it will ever be as good as hand engraving and would take a lot longer during the milling process. Not a problem, though, since I’m only intending to use the mill for “roughing out” things, to be finished by hand later.


Above, I darkened the silver for a better contrast for the photo. Well I’ll be a suck-egg mule, but the beginning of my hare-brained scheme actually came off without a hitch with a little help and advice from Apollo of Carbide3D (thanks Apollo!)… A Hobo Nickel to be (Yes, I know it’s actually a Hobo Dollar…don’t quibble…)


Well, what’s a good Hobo Dollar without a little gold inlay? We’ll add a gold tooth… Above are the basic steps of inlay – excavating the inlay pocket, undercutting the edges and raising tiny teeth in the bottom, lightly laying in the 24 karat gold wires, and finally pounding them in securely. The undercuts and tiny teeth make a strictly mechanical bond for tiny pure gold wires.


Here’s the gold inlay scraped and stoned flat, with a tiny engraved cut around the edges for excellent definition.


Inlaying a 24 karat gold tooth in the hare-brained scheme. Looking better all the time…I’m beginning to think there’s some merit to this…


Continuing the hare-brained scheme by sculpting away the little artifacts left by CNC. Now I’ll attack the chief limitation of using CNC for really fine work – the tiny milling marks that are left behind, seemingly no matter what I do. If you look closely above in the upper left, notice the fillet left by the tiny ball end mill (blue arrows). In the image in the lower right I’ve removed that little problem with a graver.


The above image has half of the skull sculpted and carved (screen right) removing the milling marks. Compare the smoother right side (your right…) to the left side with the milling marks that look like a plowed field. The right has been punch sculpted (with some carving as well) to remove the furrows…


Above is my foot controlled Lindsay Nitro G20 airgraver and the sculpting punch I used.

So you thought the hare-brained scheme was finished? No, no, no. You should be so lucky… It simply cries out for a tiny gold spider…


Above, I’ve begun the standard process of inlay – excavation, tiny bottom hooks/undercutting, followed by melting tiny balls of gold on the end of the wires. I want lots of gold to make the spider body stand proud of the surface.


Continuing on with the spider by sculpting, smoothing and trimming.


Inlaying the tiny little legs. Very fiddly work…


Above, the tiny legs scraped and smoothed. Once they’re stoned and then outlined with tiny cuts, the spider will be finished.


Above is the finished Handprint Skull Hobo Silver Dollar, so the hare-brained scheme is completed and now it’s safe to go back in the water… turned out to be not so hare-brained after all…and saved a whole lot of time during the CNC roughing out phase.

Thanks for Looking!

Tom Sterling

http://www.sterlingsculptures.com
http://www.facebook.com/TomSterlingHandEngraving#
http://instagram.com/tom_sterling_hand_engraving

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