Composites


This week, we learned how to make composites. I decided to make a frisbee, as it would benefit from being hard and rigid but also light. I designed my frisbee in Rhino and milled it on the desktop Shopbot from 2-inch foam. The frisbee is 9 inches across and about an inch tall.
Milling frisbee - it was the first day of snow in Boston this winter, and the shopbot participated!
Materials and tools:
  • Foam
  • Shopbot
  • Mold release, expoxy, burlap, release film, cotton batting
  • Clothing vacuum bag
  • Shop vacuum
  • Band saw, sander (for finishing)
After milling the frisbee, I lasercut some round burlap pieces for the layup. I opted to use 2 layers of burlap for this first experiment.
Lasercutting burlap for layup
Palash helped me set up and pack my piece in the vacuum bag. I had some trouble with the vacuum bags at first. After I removed the vacuum, the bag very quickly started to fill back up with air. I realized that I had the valve open a bit too much. A good way to tell if it was open too much was how long it took for the bag to be absent of air. In this case, the longer it took to achieve a vacuum the better, because then I didn't have to worry about it losing suction when attempting to put the cap back on the bag.
Vacuuming air out of bag.
When vacuuming, I had to hold down the area around the edges of my part. Due to the shape of my mold, I had to make sure that suction was created in the pockets around my part so the frisbee edges would lay flat.
Moment of truth!
Pulling the frisbee out of the mold went smoothly. I used the saran wrap film between the mold and the part, so it took me a few minutes to rip off some of the edges of where it got stuck, but overall it worked well. Next time, I'd like to paint the mold with gesso and use wax to ensure a smoother finish on the bottom (the saran wrap gave the bottom some very small creases).
Mold and frisbee.
To finish the frisbee, I cut the excess edges off with the band saw, and smoothed it out with the sander. I accidentally made the hole in the middle of the burlap too small, and I didn't find a good way of cutting it back perfectly roundly, so I kept it this way. Next time, I'll make the burlap pieces the right size!
Time to test!