Sun May 03 2020

Center arm rest lid

So, today I did my first composite layup. It was, ummm, an interesting experience. I felt like a one-armed paper hanger. Lots of problems. The first one was that I figured I needed about 60g of epoxy for the cloth (55g). I wanted to have a little extra, so I measured out 60g of resin in one of these little mixing cups. By the time I had the resin measured out, the cup was about 3/4 full. By the time I added the hardener, I figured the cup would be too full for easy mixing, so I transferred the resin to one of the large cups. I added the hardener, and stirred for a full minute as instructed.

The first use of the epoxy was to turn my chopped carbon fiber into a thick mixutre. It took a *lot* more epoxy than I thought it was going to. Here's the mix before spreading.

When I tried to smear this chopped fiber mixture into the joggle area just under the aluminum strips, it was clear I hadn't done a good enough job of chopping the fiber. It turned into a stringy, sticky mat that really wasn't spread-able at all. I found it strangely reminiscent of matted, tangled terrier fur. I did the best I could using my (glove-covered) fingers to spread it out.

Since I used up so much epoxy wetting down that (poorly) chopped fiber, I needed to add more resin and hardener so that I had somewhere north of 60g of epoxy. I added another 12g of resin and just over 2g of hardener to what you see here and mixed for another minute.

Ok...we're off to an inauspicious start. Whatever. Onward with wetting the three layers of carbon fiber. I poured out the entire contnents onto the carbon then laid the visqueen down.

I used an ID badge I had from SolidWorks World 2019 as a squeegee to spread the epoxy.

After spreading and squeege-ing, it looked pretty good from the top.

But, when I flipped it over, there were large areas that hadn't wetted through. F**K!

OK, time to mix an emergency *third* batch of epoxy. Here's another 20g.

Pouring the extra epoxy onto the back side of the carbon fiber layers.

After more spreading, the back side looked good as well.

I marked out the main dimensions of the lid...

...and cut the layup out. Fortunately I had an extra piece of visqueen available. It hadn't occurred to me to need one, but in retrospect, of course I need that to keep my workbench from getting gooey during this phase.

I saved the four corners I cut out. It'll be interesting to see how strong these little sample pieces are.

Here's the top layer of visqueen peeled back. At the top edge, the visqueen is folded to form the bottom layer. That was kind of a pain. It would have been better if they were two separate pieces. That way I could just peel off the top layer and discard it. As it was, I had to cut it off in it's sticky state. The alternative would have been to have a floppy, sticky layer flapping around while trying to peel it off the back of the layup.

Then it was time to fit it into the mold.

After much poking, pressing, and tucking, I had it in place. I can't emphasize enough how sticky this layup was. I'd press it into a corner with my fingers, and when I'd pull my hand out, it would stick to my fingers and get pulled back out. Arrrg!

I trimmed up the edges so that only about a half inch was sticking out of the mold.

I used the only acetone available to clean up my gloves, scissors, stir sticks (yes I cleaned off the stir sticks). Kerin was very accomodating letting me use her nail polish remover.

Time to set it aside to let it cure for a day. I hope it releases from the mold.