I figured my shoulder was well enough to start building again, so I called up Steve Robbins and took him up on his earlier offer to come inspect the workshop and maybe do a layup or two.
Steve arrived early Saturday morning and took a look at my garage/airplane factory. Aside from a few suggestions, he was happy with layout and outfitting of the shop, and suggested we do a layup while he was there. I decided on doing the F-28 bulkhead, since it was a fairly small piece.
I figured that cutting the glass for the layup was going to take about five minutes, but Steve was VERY careful about making sure the weave was straight with each piece before cutting it, and with taping the edges to make sure the cloth didn't shift after we cut it. This seemed a little over the top at first , but paid off later when laying the glass.
I started pumping the epoxy into the cup and was a little nervous when the hardener came out with a brown color, rather than looking clear like I had expected. We proceeded anyway, and I made a note to myself to check the forums to see if this was going to be a problem. I had planned to use only slow hardener for all my future layups, but since I had some fast hardener from my first epoxy order, I used a little bit of that in the mix as well for this layup. Steve suggested forgoing the first pass with with the micro, since the Clark foam was so dense there really wasn't much weight savings. I agreed, so we proceeded straight to the first layer of BID. Steve brought a 2" paintbrush to stipple with, and I found it was easier to spread the epoxy with a brush than with a squeegee, especially for a part that small. The hardest part was making sure the weave was straight. Even for a small piece that was still taped at the edges, it was tough getting the fibers to line up right until the epoxy started to set in. The second layer of BID and final one of UNI seemed to go on a little easier. Using the hair dryer helped keep the epoxy runny enough to work with, but Steve was a little surprised at how fast the epoxy seemed to be curing. We ended with the layer of peel ply tape on top, scissor trimmed it, and called that one done for the day.
We next moved on the cutting the 22 layers of BID for the landing gear hardpoints. After a few false starts (it's amazing how something so simple as figuring out the weave angle can get so confusing), we got into a nice rhythm. We used up the first roll of BID pretty quickly since I had bought smaller rolls of BID rather than one big roll. Steve was recovering from a cold and was starting to look a little worn out by this time, so when we used up the second roll, I took pity on him and told him I could finish the last few plies myself so he could go home and rest.
I came back to the garage that evening and tore the the peel ply from the layup. The finish ended up looking pretty nice, although I saw a lot of specks from the air bubbles that had formed under the layup. Some epoxy had gotten underneath the workpiece, so after staring at the underside for awhile wondering what to do, I just hit it with the Multimax sander to remove the dried epoxy (or at least rough it up enough to do a layup over it). I started trimming and was surprised at how hard it was to get around the inside corners with the Multimax half circle blade. I ended up using the sanding attachment to get the final trimming complete.
I came back out to the workshop Sunday evening to finish the other side. Since the epoxy had set a little fast the day before, I only gave the epoxy a tiny squirt of fast hardener and used slow hardener for the rest of the mixture. I went ahead and tried to micro this side of the bulkhead and ended up taking all the micro off the surface with the squeegee, so Steve was right about that. (But you know I HAD to test it myself). Getting the fibers to line up right on the first layup was frustrating to say the least - I'll have to work on laying it down more carefully. I was surprised when the epoxy started feeling thicker when I got to the UNI ply. I had forgotten to plug in the hair dryer and got it all sticky trying to get it set up. By the time I laid down the peel ply, it was already starting to gel. I quickly mixed a new batch of epoxy and poured it over the peel ply, but I left the gelled epoxy alone, since I didn't want to disturb the layup underneath. I was really confused at how fast the epoxy had cured, especially since I was using mostly slow hardener.
Or was I?
I opened up the epoxy box, noted the location and numbers on the cans of hardener, and double checked them against my MGS data sheet. Sure enough - I had gotten the two hardeners mixed up and was using mostly fast hardener for the layup. Doh! I grabbed a Sharpie and marked the two types of hardener on the hot box so this wouldn't happen again.
When I inspected the layup the next morning, it looked awful. When I tried to pull the peel ply off, most of it stayed on the workpiece. I spent the next evening sanding down the epoxy clumps and then chiseling the peel ply off. I ended up with a pretty crappy finish. Oh well.
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