The other night I finished up the steam box and made a set of little standoffs for the bottom. I wanted to keep the wood off the bottom of the box to allow air circulation, but also allow water to run back to the low point at the rear. I got a little lazy and didn’t put in dowels like most plans show.
Tonight I loaded it up with eight cap strips and let it run for 45 minutes while I went out and hung some outdoor lights on the deck. When I came back I found that the door had developed a pretty good curl — concave from the outside – and was venting a lot of the steam past the door seal. The spruce inside was fairly pliable, so I clamped three pieces in my bending form and put four more in the rib jigs. They would only fit partway down in the jigs, since the wood is swollen. While the wood cooled down I got all of the geodetic braces ready to install. I’ll glue these two ribs up tomorrow night.
I did email System 3 about their epoxy. Some of the ribs were assembled with the capstrips not pre-bent. They’re fine, but the wood will spring out of shape if it gets hot enough for the epoxy to soften. I don’t want that to happen. so I was thinking about clamping them in their current shape and steaming them to relieve some of the stress in the capstrip. Of course that will soften the epoxy, and I wanted to know what that would do. Their answer is that T-88 will begin to soften at around 120 degrees, but once returned to room temperature will be at full strength. That’s great news.
I’m definitely not in love with the geodetic rib bracing design. 24 braces, no two alike, and I’m having to hand-fit them all. It takes for-freaking-ever. I have to wonder how much heavier 3/32 plywood would be with suitable lightening holes. A guy could pop sets of them out on a CNC router in no time, save a ton of time and effort on the ribs, and probably end up with much stronger ribs too. But, I don’t think I’m going to re-engineer the ribs right now.
Last night I glued the two separated ribs back together. I cleaned off/out all of the old epoxy, sanded everything clean, mixed up some new T-88 and brought them in overnight. Just to be extra sure of a good glue cure I’ve got them warming up under a heating pad. I took one of the others to the EAA chapter meeting, no one seemed to see anything wrong with it… although the reaction varied from “Wow, that’s cool” to something closer to “You’re nuts, why would anyone do that?”
It’s cold, I’m not looking forward to the next session of shaving down geodetics for the next batch of ribs. I’ll have to go out tomorrow and do it though.
This morning I went out to check on the two ribs I had glued last night. The epoxy was set, but just a little “tacky”. It’s pretty cold out in the garage, as the outside temperature has dropped into the 20s and low 30s. I figured it was cured enough to be OK, and pulled the ribs from the jigs so I could compare the first rib out of the new jig to the others. It’s a perfect match, so I set them on the bench and went inside.
A couple of hours I went out again to do some cleanup. I found the two new ribs had pulled apart at the leading edge! The glue was still pliable enough that the “spring” from the wood very slowly (judging by the long strings of epoxy still joining the pieces) pulled them apart from the main spar forward. Fortunately I caught it before the glue had completely finished curing. With some wiggling I was able to remove the geodetics from the capstrips and clean off as much of the excess epoxy as possible without carving into the wood. I put the ribs back into the jigs, and will re-glue them tomorrow. I’m pretty sure I can salvage and repair these two, but if I’m not 100% confident in them they’ll be scrapped.
I really want to figure out an arrangement to steam the capstrips. Soaking in cold water doesn’t really seem to do much good, which is why I had not pre-bent these. Trying to soak them in hot water works for about 10 minutes until it’s no longer hot water. Two out of the six or eight I’ve bent in my former have split during that process.