Mold for 3inch compliant wheels

thingiverse

Human: "Gietmal ribbelwiel 3 inch" is our latest design for a 3-inch wheel with a profiled rim. We created this to be used with softer (shore 15) silicone, as anything stronger would probably be impossible to extract from the mold. Many people asked us to include an example of a hub, and we have now included a STL for an example hub ("hubje 3 inch ribbelwiel anderhalf hoog zonder gear"). This hub has a 4-hole pattern ready to accept M4 bolts with 16mm spacing (commonly used by GoBilda/Tetrix/REV). The original mold: This is the mold FTC team 3954 created to cast our own compliant wheels from 2-component silicone. Our goal was to make the wheels lighter and add custom-made hubs to meet our needs. It was a fun side project for some of our "intake engineers". Printing the mold: Material, infill, number of layers or layer resolution does not matter much. As long as it has a smooth surface on the inside. The largest forces on the mold are when the wheel is pushed out afterwards. Designing your own hub: The hub should have a 1 or 2 mm high, 6 mm diameter cylinder to plug the hole in the bottom. This cylinder is used to keep the hub centered in the mold. We designed it with a 4mm diameter hollow shaft, so we could use a long M4 bolt as an axle. The hub should have a diameter of no more than 22mm to ensure silicone can flow freely around the hub. The hub can be over 10mm high, but only 10mm will be covered in silicone. We designed ours with a 16T sprocket for #25 chain on top. The hub MUST have holes or "inlets" to "capture" the silicone. We found out that silicone does not stick to PLA of the hub, so you must design a way to physically attach the silicone to the hub. We used a row of thin pillars around the outside of the hub. Prepare for pouring silicone: Make sure the molds are slick and free of printing artifacts (blobs/strings). Use a sharp hobby knife or a small file. Spray the molds with anti-adhesive for silicone. We used: https://polyestershoppen.nl/siliconenrubber/lossingsmiddel-voor-siliconen-305.html Spread the anti-adhesive with a small paintbrush. Mix the silicone and hardener and mix according to the instructions of the supplier. MIX WELL! We added pink coloring (of course). We used: https://polyestershoppen.nl/siliconenrubber/siliconen-gietrubber-1-1-shore-40-594.html https://polyestershoppen.nl/siliconenrubber/pigment-voor-siliconen-316.html Each wheel takes roughly 20 mL of silicone, depending on the volume of the hub you designed. Pouring the silicone: "Pouring" silicone is challenging, so we used a large syringe (60mL) to suck up the silicone (slowly) and inject it into the molds. Although the silicone may seem thick, it DOES flow quite well into the crevices of the hub AND it levels. So make sure your mold is level, otherwise the wheel will be thicker on one side. We had a problem with lighter (less infill) hubs because they would "float" out of the center hole, so we prevented the hubs from floating with a small dead weight on top of each hub. We did not use a vacuum chamber to de-air the silicone. We did find some small air pockets in our wheels but nothing serious. We did mix the silicone more gently at the end to prevent trapping more air in and we tapped the molds on the table a couple of times after they were filled to help free trapped air pockets. Removing from the mold: After the suggested curing time (supplier) you are ready for the last stage. All surfaces in the mold are 6 degrees slanted to ensure the wheel comes out easily. By pushing a 6mm pin (bolt) into the hole you should be able to push the hub out of the mold far enough to grab the silicone. Resist the temptation to push the whole wheel out this way, the silicone CAN tear or come loose from the hub, in both cases the wheel is worthless. Just keep pushing and pulling until you can get hold of one of the spokes and pull the wheel free. THERE you have it! Your own Compliant wheel!