Yesterday I glued up the last full rib (#26) and the first aileron rib. I’m going to call this a milestone. 🙂 I now have 15 more aileron ribs to go, then 34 false ribs. I suppose I should pull out the plans sheet for the spars and see exactly what I need to order for them. I have the BOM, but it doesn’t really tell me what I need to know without looking at the plans too.
I had to look at the plans a few times. It looked like the plan sheet was calling out just one geodetic brace to omit for the aileron ribs, but the locations to mark for eventual cutting didn’t make sense. I finally realized that the text read, “Omit this X-brace for aileron ribs”… as in, BOTH braces, not just the one. Great! That’s two less pieces to cut and glue.
I finally went out and got the second rib jig from the garage and brought it down to the basement. Ribs 24 & 25 are now curing, they will be ready to pull tomorrow evening. My new routine:
Put the first jig on the bench. Cut all the pieces fro one rib and set the geodetic pieces above and below the rib caps, ready to glue.
Stack the second jig on top of the first, cut all the pieces for it.
Mix up enough glue for both ribs (14cc seems about right)
Glue up the rib in the top jig and set it aside.
Glue up the rib in the bottom jig.
Double the completion rate. I’m out of pre-cut geodetic pieces, so now I”m marking and cutting them individually with a razor saw. It doesn’t take much longer, really, and each one is cut exactly to fit.
I’m almost out of pre-curved top capstrips. The comments on the plans say you can bend the spruce dry and glue the ribs. I don’t like the idea of having that much tension on the wood. The nice thing about working indoors, though, is that I can keep hot water hot longer. When I run out of pre-bent pieces, I’ll try the hot water bend method again. In the garage the water cooled off far too quickly. In the basement, I can get REALLY hot water in a capped length of PVC, and keep it hot long enough to soften the capstrip. System 3 says T-88 works fine on damp wood… I’ll try that and see how it goes.
I finally took a minute to go out and count the ribs hanging in teh garage today. Combined with the ones in the basement, I have 22 of the 26 required full ribs. Four more and I can start on the 16 aileron ribs — they are identical to the full ribs, but missing one geodetic brace. After that will come 34 false ribs. I’m considering (maybe) using 1/16″, 2mm or 3/32″ birch plywood for those, just to speed up the process. Haven’t decided yet, and probably won’t do it because of weight. We’ll see once I get to that point.
Progress has been slow, much slower than I planned, but really — building ribs is a pretty low priority. I have knocked out half a dozen in the basement, to add to the I-forget-how-many in the garage. I’ll need to count them up soon, but I know I’m not at 26 yet, which is the count of full ribs I will need.
Got the basement workbench cleared off enough to move rib production indoors. So far I’m only using one jig, but I’ve knocked out two ribs now. I need to get the second jig set up. One rib per day isn’t going to cut it. Sure is nice working in the basement instead of the garage though.
I’ve been wanting to get back to building ribs. The garage bench has been piled too deep to get anything done, and now it’s been below zero for over a week solid. Insulation or no, it’s damned cold out in the garage. Too cold for epoxy to cure, and too cold to work.
So… there’s a perfectly good work bench down in the basement. 8′ long and rock solid, built by Dad back in the 1960s. It’s been pretty much completely covered up for the past several years with a collection of parts, partially-disassembled or -assembled prototype projects and assorted debris from the side business I was running, plus a CNC router that took up about 3′ of it. I have cleared most of it off (much of it into a trash can). The CNC machine is shelved for now; I’ll maybe resurrect it when needed at a later date. It will probably come in handy for cutting the instrument panel and/or nose ribs.
The next issue is containers for the geodetic rib braces. There are 24 braces used in each rib, all of which are of course slightly different. Just enough so that none are interchangeable. I was using paper cups to hold them in the garage, but it’s a completely unsatisfactory solution. In the basement I think I’m going to try stapling taller plastic cups along the back edge of the bench and see how that works.
I’m not moving power tools down there from the garage, so new geodetics will be cut with a razor saw. We’ll see how that works out… it’s one of those jobs I wish I could set up a machine or fixture to do. It’s 24 different lengths with over 40 different angle cuts, so I’m not sure how I’d make that work. Even cutting them out in batches on the band saw meant fine-tuning each one with a sanding block before assembly. It’s fiddly work and tedious as hell. Classic gusseted ribs would be a whole lot faster and easier to build. If I were starting this over I’d probably just depart from the plans and build them all that way; I’d probably have them all done by now.
Just so I could feel like I’m not totally stalled, I built rib #15 this weekend. 6cc of glue turned out to be just about right, with no skimping and very little excess. The new method of mixing and applying the epoxy with an acid brush worked out well. I think I will go back to an earlier idea I had, of pre-wetting the groove with glue before putting the top and bottom capstrips into the jig. It will be easy to do with the brush, and will save some assembly time. I have a template with pencil marks defining where the glue should go; I think I’ll mark the glue lines along the bottom and top of the jigs to make it easier to apply the glue.
I’ve been away from building for a while dealing with a remodeling project, the annual condition inspection on the RV-12, Oshkosh and few other odds & ends. At Oshkosh I discovered that the wood shop guys had actually saved my miniature wing rib from last year (2016). I brought it home with me, of course. Last night I pulled the staples, cleaned it up and sanded it, and gave it a coat of clear polyurethane. I figure it will make a nice wall decoration for my office.
Last night I also started cleaning up some of the enormous mess in the garage so I can get back to building. I’m not quite there yet, but tools are slowly making their way back into drawers and onto pegs. It may take a few more days, but it will be nice to get back out to a garage that’s not a complete disaster. There are 14 wing ribs hanging on the wall, and the guy on the Biplane Forum is catching up with 11 finished. He can work faster, since he can pull his ribs out of the jigs as soon as they are stapled. I need to step up my game!
I did pick up a good idea from that discussion — using cut down acid brushes to mix & apply the epoxy. They’re cheap, and it looks like I might be able to get more precise application of the glue where it’s needed, in the amount needed, with good penetration into the wood grain. I’m anxious to try that, I have a handful of brushes here. And, I got some of the epoxy into 60 cc syringes so I can dispense exactly the same amount of each component. I know it’s not terribly critical with T-88, but I still want to be as accurate as I can.
Last night I tested out the upgraded steam box door with an hour of steam. While that was going on I grabbed a chunk of scrap 2×4 and cut a second bending form. I wasn’t happy with only being about to bend three lengths per run of the steam box. I really need a better blade for that band saw… this one is cheap, and while it will claw its way through a 2×4 it’s not something I would want to do regularly.
But — I have two bending forms, which means I can now do six lengths of capstrip at a time, so I won’t run out as often. The steamer seems to work pretty well. It’s not quite as perfect as if I had attacked it with a planer, jointer and an attitude of complete professionalism… but I don’t have a jointer or planer, and even if I did what that steam would do to cheap flat sawn boards would be a real downer. It works.
On the last several ribs I’ve been taking a different approach to gluing. Early on I found that trying to glue up two ribs in one night meant working with epoxy that was starting to get a little stiffer than I would have liked. I was using a popsicle stick to carefully spread glue in the groove, then on the braces, and assembling. I was also having to fit each brace piece as I went along. Each rib seemed to want about 10cc of glue, but I was getting a fair amount of it running down onto the plastic on the jig.
Now I pre-fit all the braces and mark them with their location. I mix up the glue, dip the ends in the glue and put them in place. I can work a lot faster and make less mess. I’ve been seeing more left-over glue than I would like, as much as half what I mixed up. I think about 7.5cc of glue per rib is more than enough. I mixed 15cc for one pair of ribs and only had a little left over. I’ve also been more careful about the glue mixing. I had the ratios close enough to work well, since T-88 is not too critical. Still, the darker B component was getting used faster than the A, and that tells me I’m not getting it completely right. The stuff is pretty viscous, B much more so than A, and it takes a while to level out in the mixing cup. Now I’ve been squeezing the B part into the mixing cup and walking away for a few minutes while it levels out. Then I add the A component, walk away again, check back in a couple of minutes. I can get it dead on 50/50 that way. I may see about building a 100:83 balance scale to get it even closer.
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.