Mint Your Own Coins
I created some custom gold coins for a costume my daughter will be wearing at NY Comic Con next week. If you are curious, she is cosplaying Cleome (aka Cleophee), a character from the French anime, “Wakfu.”
There’s no chance these are going to be mistaken for real gold, but they look good enough for our purposes.
Whether it’s for a costume, a game, or just to print a big pile and roll in it, designing and 3D printing your own coins is fun. You may even learn a thing or two, like I did.
In this skill builder, you will learn how to create a simple custom model for coins or tokens in OpenSCAD. I’ll explain the basics of the tool, show examples, and provide links for 3D printing custom coins for your own purposes. You can start from my example .scad file and tweak it for your needs, and then export an .stl file for printing.
My example Kama Coins have a raised rim and a custom kama symbol that I will show you how to create. You can use the same technique to make simple geometric shapes for your own coin design.
Creating a Model in OpenSCAD
As I’ve discussed in an earlier post on designing custom dice, OpenSCAD is a free 3D Computer Aided Design (CAD) modeling tool, that lets you program your model, rather than draw it. This post is going to show you how to use OpenSCAD to make a basic coin or token shape and then add a raised geometric design in the center.
Download the latest version of OpenSCAD software for your preferred computer operating system, and install it. I used OpenSCAD version 2015.03 on a laptop running Windows 7 Professional. There may be slight differences for other versions and other operating systems, but you can probably work through those.
Create a Cylinder
Open OpenSCAD and create a new file. Save your file with a unique filename so you can find it later.
I use a lot of comments in my code, so I can recall what I was thinking later when I look at it. Comments in OpenSCAD start with a double-slash, as you can see below.
Start by making a simple cylinder, 6mm high and 36mm in diameter. This is super easy.
Press the Preview button to see what we made.
Add a Rim to the Cylinder
We’ll add a raised rim to the cylinder. Actually, we’ll subtract smaller cylinders from the top and bottom of the original one, using the difference command.
The two smaller cylinders are positioned slightly overlapping the original cylinder, one above and one below, using the translate command. The format is translate ([x-position, y-position, z-position]). We want the new cylinders to keep the same horizontal position (the x and y axes), and move in the vertical (z axis).
Then the difference command is used to subtract the two small cylinders from the larger one. Note how the translate and cylinder commands are nested inside the curly brackets of the difference command.
Press the Preview button again and you should see a rimmed cylinder that provides the basic coin shape for our model. I’m only showing the top of the coin, but there’s a rim on the bottom as well. Don’t trust me? Rotate the model in the display area and check for yourself. You should see a red indented surface on the bottom of the coin.
Forming the Geometric Symbol
Next we are going to make the kama symbol. It looks like a capital “K” with two horizontal bars through it. The bars have slanted ends.
We’re basically going to build it by using the letter “K” and adding some polygons on top of it, and joining them all together with the union command.
First, we need to define our font, letter size, and letter height using variables. I inserted these lines at the top of the code, right below the initial comments.
Starting with the bottom side of the coin, we now add the letter “K” with the text command. Text in OpenSCAD is 2D, so we have to use the linear_extrude command to add some height to the letter. The rotate command is used to position the letter where we want it.
Once again, press the Preview button, and make sure it looks something like the picture below.
Now for the horizontal bars. We use the polygon command to create the basic shape we want. Repeat the command to get two of them. We add these lines inside the same linear_extrude command block we used for the text. The translate command you should now be familiar with places each of the polygons where we want them.
Finally place the extruded text and polygons within a union. The union command is a Boolean operation that adds shapes together.
There we have it, a nice kama symbol on the coin. It is important to note that the bottom of your coin will not be supported when you print. Therefore large recessed areas may not print well. I made my kama symbol as big as possible to try to limit the unsupported area.
Now that we know how to create a 3D kama shape on the bottom, we just copy that code for the top, and re-position it using the translate command. We also need to use the mirror command to flip the symbol around the y axis. The format for the mirror command is similar to the translate and rotate commands. However, we are not working in degrees. By placing a 1 in the y axis argument of the mirror command, we flip the image so it looks right.
Press Preview and check your work.
Looks like we are done, right? Well, not quite. Although our model looks all joined up, it is actually still in three pieces: our basic coin shape and the two kama symbols. Join them all together by wrapping a union command block around all three. Don’t forget to close the union command block with a squiggly bracket at the bottom.
Render the Model and Export the STL File for Printing
Once you are happy with your model, you need to render it. Click the Render button and see if it completes without error.
You should see the rendered model in the display area, and the result of the operation in the console area below that.
Finally, export the model to an STL file for later printing.
I used Cura version 15.04 on a Printrbot Simple Metal, and I was very happy with my results. I printed in PLA with a layer height of 0.2mm and the shell and top/bottom at 0.8mm. If you make the top/bottom too thin you will get gaps.
Printing in one piece worked well for me, but the bottom may be a little stringing where it is not supported. I tried to make the model as good as possible for printing in one piece. Printing with support did not help.
You can use your printing software to print only the top half of the coin (Cut off bottom in the Advanced tab on Cura), print two of them, sand the bottoms flat and glue them together, but that’s a lot of work and I’d rather live with a slightly stringy bottom half of the coin.
You can find the files for my Kama Coins on Thingiverse.
Don’t just stop with my example, try something on your own! Work with different symbols, print coins with your own profile on them, etc. Have fun!