The mold “box” base was an aluminum plate with the bolt hole pattern drilled into it. This was then used to hold the master (aluminum) wheel down to the plate. I then hot glued a bucket with the bottom cut off around the wheel.
Yes, the top side is as smooth as the urethane is poured. Some of our wheels have just the poured urethane surface on top. As we tweaked the process though, we added more glass to the urethane, which resulted in a “bumpier” surface on the top. To enhance the look of the wheels we did start pouring high and machining the excess away. One of the enhancements to the process we are trying to make is to eliminate that step, although it only takes a minute or 2 for that operation per wheel.
Our pieces of glass are between 3/8" and 1/2". Right now to measure the amount of fiber we place in the mold, we place the chopped fibers in a cup and gently tap the cup on a table to flatten the fibers out a little bit. We use the same style cup to measure out the urethane needed for the wheel. We then use a 1:1 ratio of urethane to “tapped down” fiber by volume. Our wheels typically needed about 80 mL to fill the wheel safely, so obviously for the 80 mL of urethane, we needed around 80 mL of tapped down chopped fiber.
The amount of fiber we use is something we still want to play around with. I feel with the geometry tweaks we plan on making that we can reduce the amount of fiber necessary.
We used chopped fiber at the time because we had cloth laying around that we could use right away. Certainly playing with the size of the fiber would be another variable to explore, and is something we’ll certainly be looking into.
They have a huge selection of materials to choose from. You can use their data sheets to pretty effectively choose a resin yourself, however their customer service is also super helpful, so if you are not sure, feel free to ask them.
The different resin sizes come in pretty handy as well, where trial sizes are cheap and get you a couple parts, and larger sizes can help get you through a large run.
We used Task 9 for the wheels, however that may not be the best choice for whatever application you are considering. I highly recommend doing a little research for yourself and coming to your own conclusions so you know for sure that you are using the best resin for your needs (and you’ll get to learn a bit too about mechanics of materials and material science!!)