Our CNC operator did this project as a personal project and it came out so cool we decided to share it.
First he downloaded a file of the Rebel Alliance symbol and took it into Fusion 360 and redrew it and modeled it into a 3D object with a border to get the cut file needed.
Next he cut out the the relief areas to pour the resin into with the CNC router. For this project he used some baltic birch plywood plywood due to it having lots of thin layers of equal thickness and very few core voids. The CNC cutting on this project is done in 2 operations, the first operation is to cut out the pockets to cast the resin into and the 2nd operation is to cut the coasters out of the plywood sheet. For this reason it is important to set up the cutting in a way that you can take the sheet off of the machine and load it back in again without loosing your zero reference for cutting. The pocket depth on this project was 1/8-3/16 deep, in hindsight it may be a good idea to go deeper in the ring pour and on something this small there is no reason why you couldn’t with any of the hardener speed configurations.
Once cut it was time to get casting. We used the clear Contemporary Composites Technologies (CCT) resin on this cast. In this case the castings are so small that there is no need to worry about issues from the resin getting too hot as it cures so he used the fast hardener. With this pour he also used a variety of powder pigments to get different effects. The cool thing with powder pigments is that they are reflective and move in the resin so you can get really neat looks, textures, swirls, etc.
After casting these will get surface planed, so it is OK if they get a little overfilled as you can see they did in this case. One thing about the sworls and such is that as the resin cures it can be helpful to come in with a wire and move it around to get different effects. This particular resin is really runny to begin with but as it cures it gradually gets thicker, during that time that it begins to thicken it can be a good time to play with adding texture by moving it with a wire. Keep in mind this is more an art than a science for getting the look you want.
After surface planing on the CNC router (which could also be done with a sander or a router sled) and perimeter trimmed he sanded them down a little further to get out the milling marks and to slightly round over the edges before clear coating.
You can clear coat with the same resin or with another coating if so desired, in this case he used a product called Duratec Sunshield which provides a hard, buffable clear coat that is also UV inhibited and UV stable so that it will protect the substrate below it. For the coasters that might have been overkill but if it is a project that is going to be outside Sunshield is an excellent option to protect from UV damage.
