Introduction: Make Your Own Custom Coin
Link for the video in case it doesn't show up: http://www.youtube.com/watch?v=jhASjoxSpkE
Have you ever wondered if you would look good on a coin? This is your chance to find out!
In the past making your own coin was an ordeal and a half, having to carve out a die and strike malleable metal under several tonnes of pressure. These days, it's as simple as making a 3d model and sending it to a CNC mill for machining. Follow along on the journey of making your own custom coin (and a box to go with it).
- Brass stock
- CNC milling machine capable of milling soft metals
- 3D modeling software (Autodesk 123D Catch, optional)
- 2D photo editing software
- Engraving cutter
- Files/sand paper
Let's get going!
Step 1: 3D Model Your Head
Here you can use two methods to get a 3D model of your head, unless you happen to be fortunate enough to have it scanned with a high quality 3D scanner.
One entails using a software from Autodesk called 123D Catch which can stitch together a 3D model from a series of photos taken of your head.
The other method means building a depth map from a photo to displace geometry into a 3D relief for use on a coin.
Go to step 2 for the 123D Catch method, and step 4 to learn how to make a depth map. Either method is unfortunately a bit time intensive, but both yeilds great results.
Step 2: Autodesk 123D Catch
The perhaps easiest method is to use Autodesk 123D Catch. I won't go deep into it's workings, as there are many, and better, tutorials and videos explaining it's use around the web, not the least here on Instructables.
The idea is though that you need to have someone take a lot of photos of your head, from every conceivable angle. For this you should not move, and the images need to be sharp, and have as big depth of field as possible (meaning if you focus on the nose, the eyes still remain sharp, etc). If your image isn't sharp the results will reflect that and be rather poor.
Be prepared to take 50-100 photos, at least, to cover an entire head. However, if you're using it for a coin you may be able to get away with less as you may only need one side of the face.
Once everything has been shot, process them through 123D Catch and get a 3D model which you can continue to manipulate in your 3D software of choice.
Step 3: Modeling
Once you have your model, and you have polished it to whichever finish you have, all you need to do is bisect it down the middle and squish it down so it fits on your coin.
Model the rest of the coin around your head, and make sure it is to scale with your intended final coin.
Step 4: Depth Map
Making a depth map is quite a bit more intensive, and does require a fair bit of manual labour as well, but will give great results if you take your time.
The idea behind a depth map is an image where things are brighter the closer to the camera something is. The closest part of a subject to the camera is colored white, the furthest away is black, and everything in between is a gradient of gray. Unfortunately, there is no easy way to simply convert a photo to a depth map, just converting it to grayscale won't work.
In your photo editing software, start by converting the photo to black and white, adjust the contrast and brightness. Then you need to start to manually push and pull values in the photo to become brighter, and darker, to get the depth map to how it should be. There is no magic to it, just a bit of work. Using burn and dodge can be a great way to push those values around. For hair, it can be a good idea to isolate it on its own layer and invert the values, as that will make it stand out (as long as the person has dark hair).
You may need to go back and forth between your 3D software (I will cover this in the next step) and your photo editing software to fine tune parts as you're working on it.
Step 5: Modeling
In your 3D software you need to find the function to displace geometry using the depth map you just made. Basically you will push polygon geometry differently much depending on the value of the corresponding pixel in the depth map. If a pixel is white it will be pushed a lot, gray less, and black not at all, in the end creating a relief of the face you made.
This may be done differently in different software, in Autodesk 3ds max it's called Displace (it's a modifier), in Rhinoceros 3D it's called heighfield, but may be called different things in other programs. Some programs, like Solidworks, lack an easy way to perform this function.
Once it's done and you've tweaked the depth map so your face relief looks like it should you can model the rest of the coin around it and go on to the next step.
Step 6: Side Track
Now that you have your coin all fancy and 3D modeled there is certainly nothing stopping you from forgoing the entire CNC route and just 3D print your coin instead, even in metal. There are several services which offer this option, but my personal favourite is Shapeways. Bear in mind that a metal 3D printed coin will be many times more expensive than one which you mill out yourself, but if you don't have access to a CNC mill, or the money to buy one, and you're only planning to make one coin it could very well be a viable option.
You could check out my other instructable Making Your Own Branding Iron for more on metal 3D printing.
Step 7: Setting Up CNC Mill
To mill this coin we're going to be using a Roland MDX-40a CNC mill. Unfortunately this mill was not intended to mill metal, not even soft ones like the brass we're using, so we need to make some adjustments to make it work like we want.
A word of caution! Since this mill is made for softer material it's usually enough to use double sided sticky tape for the work holding. I made the mistake of trying that, as can be seen in the image using the thick aluminium block for a base. Don't repeat my mistake, as when milling metal you introduce much more force and vibration into the machine. If the tape doesn't come loose entirely it will still not be rigid enough to hold the stock still, and the resulting vibrations will make the end result quite rough, not like you'd want to see on a coin.
Because of this an entirely new bed was made for the mill using some thick aluminium plate, into this four holes were drilled and tapped at known positions, and corresponding clearance holes were drilled through the stock to mount the brass in the mill. This will be a rigid enough setup for the machine not to vibrate itself to pieces.
Since we're going to mill both sides of the coin we need to be able to make sure that the back is aligned with the front. Using the four holes we drilled in the stock, find the centerpoint and mark it. In the mill use this mark to set the X and Y zero points.
Make sure everything is tightly held down and move on.
Step 8: Milling!
This is where you're going to have to experiment a bit to find the speeds and feeds which work for you. Be prepared to ruin a piece or two while dialing in the correct settings. The Roland MDX-40a mill has an overload protection, so if you push the mill too hard, and the tool can take it, it will jam and shut down.
Then again, if you don't push it enough the milling operation will take absolutely forever. If you have a stronger and more rigid machine you can definitely go faster without introducing chatter and vibrations.
For the tool we're using a 90 degree engraving cutter. This also has to do with the underpowered mill, as this tool will have less contact with the stock than a ball ended endmill would. Again, if you have a better mill, you could use the ball ended endmill to hog away most of the material in a roughing pass and then change to the engraving cutter for the last little bits.
I found that milling the coin in a spiral path from the center out produced best results, as compared to milling following the X and then Y axis, but you may have to experiment to find what works for you.
Step 9: The Flip!
When the front is done, remove all the dust, flip it and screw it back down. Do not rezero or reset the X and Y origin points, they should remain in the same place as when you milled the front. If you were fastidious in centering on the mark on the front of the coin the back should mill aligned with the front. While doing it all by eye isn't the most exact method, with care you can still get it within a fraction of a millimeter, close enough for no one to notice if the alignment is off.
Of course, you don't have to mill the backside, but a one sided coin is just a medal after all.
Milling the back is just a repeat of the front, just with different 3D geometry. Model yourself a fancy coin, or make a replica of an already existing one, just don't try to pass it off as legal tender. Then again, considering the time and effort which would go into making this you'd be crazy to try to make a quarter or two to use as payment.
Step 10: Creating the Rim
As the mill was underpowered the entire coin was not milled out, but a small ledge was milled around as much of the cirumference as possible without crashing into the screws. This ledge could then be used as a guide when clearing away most of the rest of the material on a belt sander. There's of course nothing stopping you from simply filing away the rest of the material as well.
A file was put up against an angle plate and the coin filed against it while pushed down against a flat surface. This created a nice right angle around the coin, and got rid of the unsightly marks left by the belt sander. This is a bit of a long process, but it gives a very nice result in the end.
The plastic was put down to not scratch the coin during these operations.
Step 11: Patination
You could stop here, and you would have a very nice coin. However, it is just bare brass, and it doesn't have much depth or life to it at the moment. You could just handle it and over time it would build up oxidation and grime enough to look interesting. Or if you're impatient, like me, you could create your own patina pretty simply
With brass, as it contains a lot of copper, there are many ways to oxidize and create a patina. There is a compound called liver of sulfur which is very good at this specific task. You can also hard boil an egg, smash it up and leave it with your coin in a sealed plastic bag (don't let the coin touch the egg though) over night, the sulphur in the egg will create a patina on the brass.
Not having access to liver of sulfur and having eaten all the eggs made for another way to create a patina look. First the coin was burnt with a blowtorch enough to dull and oxidize the surface of the metal. It won't create a dark oxidation, but more of an unsightly brown patina.
To fix that we're going to grab a can of matte black spray paint. Yep! Spray paint! Just give the coin a quick coat and before it dries wipe off as much paint as you can. This will leave paint in the recesses and make it look quite dirty and even more unsightly.
Final step, and here is where the magic comes in. Once the paint has dried thoroughly, take some metal polishing compound, like Autosol, and polish the high spots of the coin. This will bring the shine back and give a nice, multi-layered, patina on your coin. The burnt oxidation will shine through in places, and the black spray paint will stay in the recesses.
If you find that the paint has gone a bit grayish after polishing you can just treat the coin with a bit of linseed oil. It will absorb into the paint, darkening it, and then harden over time so your coin won't stay all oily.
Step 12: Done!
And your coin is done! Present it to whoever you want to give it to, or keep it for yourself constantly reciting "My preciousssss" every time you handle it, the sky is the limit.
Of course, if the sky truly is the limit, and you're planning to give this to someone, why not put in the extra little effort and make a nice container for it. Read on for how to bump your coin up another level!
Step 13: Box!
If you have access to a CNC mill already making a box for your coins should be fairly trivial.
Here we're using a piece of oak, cut in half and opened up so each side of the box will match when closed. Into this three recesses for coins were milled, each a fraction bigger than the actual coin so they wouldn't bind in their positions. The front of the recesses were also milled slightly deeper than the rest so the coins could easily be extracted by pushing the front down so the back of the coin pops up.
In the corners of the box four smaller recesses were milled in to hold magnets to keep the box closed. A drop of super glue when putting them in ensures they won't move out of place.
Cutouts for the hinges were also milled while milling the circumference of the boxes, so the hinges would sit flush with the body of the box.
Once you've milled it out just give it a light sanding and treat it any way you feel like. Give it a nice coating of mineral oil, or why not varnish it to make it shine!
Step 14: Bonus!
If you're shooting material in a dusty or grimy environment and you're worried for the well being of your camera. What if you can't afford an underwater housing just to use in your workshop? No worries, saran wrap (or cling film) to the rescue! Just cover up your camera in the stuff, and make sure you stretch it over the lens so no folds or bumps are there to distort the footage. Sure, it's not the best solution, but it will definitely do in a pinch!
Step 15: Thank You!
Now go out and conquer the world! Convince your friends you were once the ruler of a long lost nation! Incist that your currency is good for a venti latte at Starbucks! Heck, do whatever you want to!
Thanks for checking out this instructable! Remember to subscribe to my YouTube channel, and follow me here on instructables for more future projects like this.
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