Epoxy and Fabric Composite Paddle


I have a kayak that I bought for Rush at East Campus and I haven't had a chance to use it yet because I don't have a paddle. What better way to remedy the situation than composites week at MAS.863?!

I drew up model in Solidworks of what I wanted the paddle to look like based on some research into lightweight wing paddles. I then made a drawing of the part and took section views at one inch intervals. I then cut out ~1/8" thick cardboard sections with the laser cutter and secured them together in a skeleton. I cut out a slot in the cardboard for the shaft and then wrapped the whole thing in shrinkwrap.

I was unhappy with the stiffness of the Smooth-on polymers that we have available in the Fablab, so I picked up some West System resin and hardener that was laying around at MITERS. Apparently the mix ratio is 5 parts resin to 1 part hardener, so I eyeballed those amounts into some into some glass (I couldn't figure out why the directions recommended not using glass containers - maybe precaution against breaking?) jars and carried them back to the Media Lab. I also picked up a 1.25" diameter, 6' long wooden dowel to use as the shaft of my paddle. I cut out 2.5" wide strips of the tan cotton fabric and dipped them in the mixed epoxy solution, which has a pot-life of about 20 minutes. With gloves on, I made sure the epoxy was thoroughly impregnated in the porous fabric and then draped the layups over the skeleton. Because I was only covering a single side and wanted to remove the skeleton, I first covered it in some pink release film. The layup layer count varies from 3 (5 if you count the layers holding the shaft in) along the central axis of the paddle to 1 at the very edges. Finally, I put on another layer of release film, a layer of cotton absorbent and stuck it all in a sealed bag for pulling a vacuum. I left it under vacuum for about 15 minutes, or until I could see that the excess expoxy had become quite firm.

After Setting:

I took the composite back home and let it fully harden overnight. The next day, I removed all the now superfluous vacuuming paraphernalia and trimmed the edges of the composite paddle. I was quite pleased with the result, despite the shaft not fitting as snigly as I would have liked. Tips for next time:

  • Find a better way of thoroughly impregnating each fabric strip with epoxy
  • Use thin wood for the skeleton instead of carboard
  • Make sure the support for the shaft is wrapped snugly around the shaft and firmly connected to the rest if the paddle.
  • Use one more layer of fabric