I recently lost an entire set of pieces to one of my favorite board games, Settlers of Catan, and I couldn't find any easily accessible replacements without buying a whole new copy of the game, so I decided I would make some. I wanted to be able to create pieces with a unique color to (hopefully) impress my friends when we next get together to play, and since I had access to a Nomad 883 milling machine I decided to design a mold. To make small plastic pieces I needed a rubber mold, which itself needed a mold, and a bit of patience. With this design I can make pieces in any color imaginable; I chose purple because it is not found in the game, and makes for vibrant plastic pieces. This technique could be adapted to any board game pieces, and mold for the rubber could even be 3D printed if that was what you had available.
Step 1: Materials Used
- Square block of medium density polyethylene (MDPE) or milling wax or equivalent
- This can be any size as long as it will fit your design and your milling machine
- The better the surface finish of this material the better your final design will come out
- #201 Bit (Square 0.25")
- #102 Bit (Square 0.125")
- Nomad Milling Vice or equivalent
- Smooth-Cast 325 Pigmentable Liquid Plastic
- So-Strong Purple Liquid Urethane Colorant
- Mixing cups
- Rubber gloves
- Newspaper or other work surface protector
Step 2: Measure the Pieces
To make sure that the pieces will fit in nicely with the regular board game, I measured the edges in mm so that I could recreate them. For my project I decided to build a city, settlement, and a road, but if you wanted to expand on that, making any of the other pieces could be done in a similar way.
Step 3: Design the Model
To build the 3D model of my pieces I used FreeCad. Any 3D modelling software can be used provided that it can export files in a .stl format. To begin I built a 52 X 115 mm base, because I had a piece of medium density polyethylene (MDPE) in those dimensions. Using the sketcher and part design views I drew and extruded 5 roads to the proper dimensions, leaving 5 mm between each for the cutting tool to pass through. For the settlement and city I built block shapes and used the pocket tool to cut away the corners. After the pieces I wanted were drawn I added an enclosure around everything and extruded it up 15 mm (5mm higher than the highest piece, keeping in mind that the city was on its side) so that there would be a stable bottom for the rubber mold.
Step 4: Prepare the Milling Files
To generate the .nc files to run the CNC machine I used MeshCam V6. A license for this software came with my offices Nomad 883 CNC machine, and works well for this tool. To start with I import the .stl file into MeshCam, and select the machining region. Since I want my design to be cut out of the plastic, I don't need the outside machined. By setting the machining region to just be the inside I can save quite a bit of time during the actual machining. MeshCam has a great automatic toolpath wizard that I used, where I specify the roughing tool (#201 tool) and the finishing tool (#102). I chose tools with square edges to make sure that the bottom edges would be sharp. After generating the toolpath save it somewhere you can find it later, and you're ready to move onto the next step.
Step 5: Zero Your Axes
To mill out my creation I used a Nomad 883 pro CNC milling machine, with the carbide motion software. To secure the plastic I used the Nomad drilling vice. Using the jog tool get your drill bit right to the edge of your material. I use a small piece of paper, and gently slide it back and forth under the drill bit while using small increments to move it closer, until the paper can still be removed but with resistance from the drill bit. Make sure you know which axis you were moving, and zero that one. Go on to zero the other axes, making sure that you don't jog the drill bit into your material as this could break it. Always zero whichever bit you are going to use first, for my project I zeroed with the #201 as it was my roughing tool, and when I changed to the #102 I re-zeroed with that bit.
Step 6: Mill Your Design
Once everything is set up, load your .nc file into carbide motion and mill your shape. The pictures I took of the finished product are post clean up, and don't show the incredible mess that milling machines can make. Make sure that plastic chips aren't going to fly and hit something delicate, like your eye. The Nomad 883 Pro has a great screen to catch any flying debris. Once your milling is done it is important to make sure that it is cleaned out thoroughly as any defects inside the blank will transfer to the rubber mold, and the eventual finished plastic.
Step 7: Pour the Mold
To make the mold I used Smooth-On Mold Star 16 FAST Platinum Silicone Rubber, which comes in two parts. After ensuring that the milled plastic mold is clean and dry, measure out two equal parts, both approximately half the required volume to fill the milled mold. Stir each independently using different stir sticks, and then mix it together. This rubber is an irritant to your skin and eyes, so make sure to wear gloves, and do this in a well ventilated area. If you do get any on your skin or eyes, follow the MSDS instructions included in the packaging. Once mixed, the rubber will start to set, so the faster you can pour the rubber into the mold the better. To help free some of the bubbles that may be trapped you could put it in a vacuum chamber, but I find that gently tapping the mold is enough. This could get messy, so make sure you either put paper towel down like me, or do this somewhere you don't care too much about the work surface. Once you are satisfied with your result let it sit. I like the fast setting rubber, which I let sit for about an hour. There are a lot of great videos on Youtube about how to use Smooth-on products to achieve different effects, so if you're interested in molding I recommend checking these out.
Step 8: Remove the Mold and Pour the Plastic
After an hour the rubber mold should be ready to be removed. Gently lift away at the edges, until you can start pulling the mold out. Any residue from the MDPE mold will likely come out with your rubber, and if you need to its okay to redo it. After you are satisfied with your rubber mold you can mix the colorant into Part B of the liquid plastic, and mix it to an equal amount of Part A. Smooth-Cast 325 cures quickly, much faster than the rubber so don't linger. As with the rubber, follow the safety guidelines outlined in the MSDS included with the plastic, and make sure your surface is protected as getting this stuff off is quite difficult. Let the plastic cure for 30-40 minutes before removing it from the mold. After 20 minutes it is okay to touch, but may still feel tacky. When handling the liquid plastic it is important to use rubber gloves, as this stuff can irritate and stain your skin.
Step 9: Pop Out the Pieces and Repeat
Once the plastic is hard enough you can pop your pieces out of the rubber mold, similar to popping out ice from an ice tray. Since I only designed a small number of the pieces, I just kept making the plastic copy until I had a full set, in order to reduce the amount of MDPE and rubber used. If your plastic parts have a bit of excess on the edges from the pour you can file it down with a nail file, or clip with small scissors. This technique is great for building lots of the same small plastic parts, and the finish and resolution comes out better than if they were 3D printed, with more options for materials (I could make Catan ice cubes or chocolates using a food grade rubber mold). The finished pieces came out more black than purple, but they still look great and fit in with the other pieces!