I've always been interested in Eadweard Muybridge's pioneering work in photography; especially the task he was given to prove that the legs of a horse come completely off the ground when running a full speed. In the Title picture above, can you find the frames where the horses feet leave the ground? I can't believe this ground-breaking event occurred in 1873!
While reading about Muybridge's Zoopraxiscope, which is based on stop-motion photography, I got an idea about making a custom-silver coin, that in conjunction with mobile camera frame-rates, could simulate what Muybridge did with his "Horse in Motion" event.
In the following pictures, you can see my progress in creating this coin. The first picture shows the "horse running cycle" vectors that I purchased from Shutterstock. That site has running cycles for just about any animal.
The next .gif file shows the twelve horse models galloping. I created the models from the Shutterstock vectors, using Extrudy. Then I used Aspire to rotate the vectors 30 degrees and capture the screen. I also used EZGIF.com to create the GIF from the screen captures.
The next picture shows the final preview of the coin as it was designed in Aspire. Aspire's preview is pretty amazing to me. It's usually WYSIWYG from the CNC Machine, as long as you program Aspire with the bits you actually plan to use.
Note: The 0.3 mm bits look very similar to 0.5 mm bits if you're not paying strict attention to what you're doing.
The next picture shows the silver coin that I designed in Aspire. This took my Sable 2015 CNC Machine just over 3 hours to carve. Most of that time was dedicated to the Finishing Toolpath--1' 47". The Roughing Toolpath took just about 44".
The next two pictures show the ring that was formed from the silver coin. The tumbler I used smoothed the details of the horses down a little much, but for a first try, I think it turned out okay.
I used a couple of programs to create the "12 Galloping Horses" Coin. The first program I already mentioned--it's called Extrudy. This free program is available for Windows and Android (what I use) and was so easy to use since the Shutterstock horse vectors were solid black against a white background. This is exactly what Extrudy needs to create 3D models.
The other program I used to model the coin (for carving) was Vectric Aspire. This is the program I usually turn to for most of my carving tasks, but to be honest, if you use Extrudy to make your 3D models, you don't really need the extra horsepower that Aspire provides. I have been using Vectric products for a while, so I suggest importing the models into VCarve Pro. Then you can use 3D Roughing and 3D Finishing Toolpaths that VCarve Pro provides, to carve the coin from silver, gold, or copper.
The next step is to make these coins faster. I'm seriously thinking of commissioning a company to make me some custom 2-sided dies. Then I can use a contraption to stamp double-sided coins at my leisure. Sweet!
1. Out of Spec Precious Metal
The first sheet of 12 Gauge 925 Sterling Silver I used happened to be the only one of three sheets to measure incorrectly at 1.22” x 6” versus the specified 1.25” x 6”. In order to use the silver sheet (purchased from Rio Grande) that did not meet our specification, I redesigned the double-sided coin to be smaller.
Discovered after breaking several bits (0.8 mm and 0.3 mm) that the outside edges of the silver square (1.25” x 1.22”) were 0.05 -0.1 mm higher than at the middle of the sheet. The single wood screw that I employed to hold the silver sheet down into the mount put unequal forces in the middle of the coin versus supporting the whole square. Added L-shaped metal brackets to better hold the sheet down uniformly flat.
3. Too Fast and Deep CNC Machining
Broke a 0.8 mm ball nose bit during a Roughing operation. This may have been due to my attempt to carve un-annealed silver with increased feeds & speeds. For success, I lowered the depth of cut from .15mm to .10 mm. and annealed the silver sheet.
Broke several bits (0.3 mm ball nose) during Finishing toolpath operations due to a 3D design issue where the offset of the Finishing toolpath was too small (0.15 mm should be okay in normal circumstances). This caused the small bit to scrape the ragged outside walls leftover from the roughing toolpath. Changed the offset to 0.3-0.5 mm to ensure the bit cleared the walls.
Discovered late in the double-sided operation that one or more toolpaths did not carve centered in the silver square. This problem is caused by several factors. For one thing, I’ve verified several times during the design stage that some part of the 3D design was not centered in Aspire. This is a huge problem that must be resolved by better situational awareness. If you get the design under control, there is still the physical mounting of the silver sheet that must be centered. Maybe more significantly, I found that the wood mount was not exactly equal to the size of the silver square. The mount was actually 1/32” larger than the silver square in each direction (x and y). Lastly, if using a wood screw to help hold down the silver square to the mount, it must be screwed into the wood straight. If it is screwed into the wood crookedly, it can possibly shift the silver square in both the x and y directions; especially, if the mount is larger than the silver square in the first place.
Hi there! I've been refining my Coin Rings over the years, and I wanted to document what I discovered during my experiences. In this Kindle book, I pinpoint the problems I see with all coin rings made from currency coins, and provide what many coin ring makers, including me, do to mitigate these problems. I go one huge step further and provide a path for those wishing to use CNC Machines to make better rings. I love the ability to create coin rings using coin ring making tools and the procedures and skills I have developed. Now I make custom, double-sided, precious metal rings using these tools and skills along with my desktop CNC Machine. By the way, the rings shown on the Remarkable-Rings Welcome Page were made using coin ringing tools and the CNC Machine.
Do you own silver coins that have grime or tarnish in their crannies? I sure do. Take a look at this pile of junk coins I bought from an Ebay seller.
As you can see, most of these coins are pretty tarnished. Here are the steps I take to clean up grimy coins.
Here we have 3 Walking Liberty half dollars. Notice the grime in the cracks.
First step is to heat up the coin to a dull red, and then quench it in water.
Here is the coin after pulling it out of the water. Lots of fire-scale; ready for pickling.
Next step is to drop the coin in a hot batch of Pickle.
The pickle will remove the fire-scale and leave a pristine white coin.
Next step is to use a brass wire bristle Dremel attachment to strip away the whiteness and reveal the prized shine.
Mark Unger has been called the Renaissance man by his peers for all of his successful pursuits on the job and in his spare time. Among other interests such as 3D printing, CNC milling, woodworking, and electronics, Mark follows the developments in Coin Ring Making.