#2 rib glued

I spent some time cutting geodetic braces.  I stacked five of the thin capstrips, laid out the parts along them, and cut them with the bandsaw.  I now have enough parts to make half a dozen more ribs.  It’s slow going with the geodetic capstrip, because each one has to make three passes through the spindle sander to shave them down to 3/32″  Holy crap that’s tedious.  I may try using the table saw when the thin strip rip jig arrives.  Even if I can get them close enough to just make a single pass on the sander it would be a huge improvement.

I tried a different technique for applying the glue.  First I dry-fit all of the parts to make sure I didn’t end up with a brace with glue all over it that needed to be trimmed.  I marked the top and bottom capstrips with a pencil to indicate where the groove needs to be glued.  Then I pulled them out of the jig and used a trimmed-down popsicle stick to apply epoxy to the grooves.  Back into the jig, with the front and rearmost vertical pieces in place since those are impossible to install with the capstrips in the jig.  Then I proceeded as usual, installing all the other parts with epoxy.  It worked like a charm, and resulted in no glue running down where I didn’t want it.  We’ll see how this rib looks when I pull it out of the jig tomorrow…  and we’ll see how closely it matches the first one.  In theory they should be identical, but I’ve  never done this before, so…

Rib #1 out of the jig

This morning I pulled the first rib out of the jig to check it out.  I was a little apprehensive about it, to be honest.  I had tried to use a little digital scale to weigh out the epoxy, and that didn’t work well.  The scale didn’t see tiny increases in weight as “activity” and would power itself off every few seconds.  I ended up “eyeballing” the mix by volume, and hoped I got it right.  With a little less than 15cc of glue I was hoping it was right, and last night it was still feeling a little “tacky”.  Well, this morning that epoxy is perfect, nice and hard, glossy surface and zero tack.  My test piece with a couple of scraps of geodetic brace glued with no clamping broke apart in pieces, with no failure at the glue joint.  The wood failed and the glue didn’t.  Success all around.

The only deficiency I can see is, there’s maybe a little more glue than needed.  Glue had run down under several of the joint areas and I have some cleanup to do on the “bottom” side of the rib, the side that was against the jig surface.  I’ll need to figure out how to get the right amount of glue in there when I pre-glue the groove.  Other than that, it looks really good and I’m thrilled with it.  It looks like about 10cc is what is needed to glue up a complete rib.  That means when I get the second jig built, I can mix up 20cc and glue two ribs at a time.  The more glue gets mixed at one time, the easier it is to get the mix ratio perfect so that will be good.

And, I’ll have to put this rib somewhere in the middle of a wing where it can’t be seen by the Oshkosh judges.  That way it won’t screw up my chance at that gold Lindy.  🙂

First rib glued!

After a couple hours of cutting and sanding geodetic pieces, I finally mixed up a little T-88 epoxy and glued up the first rib.  Kind of a milestone — the first full size wooden rib I’ve ever built.  Can’t wait for tomorrow when the glue is hard enough to pop it out of the jig.  Then we’ll see whether this one gets used on the airplane, or used for destructive testing.

Cutting those geodetic pieces is a lot of tedium.  Even more so since I didn’t send the strips before cutting, so i then had to sand each piece individually.  next time I’ll clean up the capstrip prior to cutting.  I was cutting two pieces at a time, with the capstrip stock taped together.  I may go for 4 or 6 pieces at a time as I get better at it.  And, I need a better solution for holding the pieces.  I knocked three of those cups off the bench at various times while assembling it.  Things will be a lot easier if and when Pete’s R/C Cub gets off my workbench.

Shaving the geodetic pieces

Yesterday I tackled the problem of the rib geodetic pieces.  The thinnest I could order from anywhere was 1/8″, and the plans call for 3/32″ thick.  What I got from ACS was actually a bit oversized at .130 to .140.  So, I need to shave about .040 to ..045 or so off of 120 or so 6′ long strips of spruce.

I tried a small razor plane…  no joy there.  Maybe it was my technique, but the blade dug in and left a very rough, uneven surface.  It’s quite possible I could make this work with a “real” hand plane, but I’d have to go buy one, then learn to use it properly, and let’s be honest — right now I’m a little impatient to start building.  I tried spinning up an end mill in the CNC machine, but it was obviously over-taxed and would take several passes.  Probably the wrong tool for the job.  Maybe a router bit would have been better, but there was also a work space issue, and the small motor and flex shaft drive was not going to be up to the task.  I knew I was fighting a losing battle there.  My Harbor Freight belt/disk sander seemed promising, but the top roller on the belt is convex and was leaving a concave surface.  I was not too confident in trying to use the table saw to shave them down, given how quickly things can go wrong there.

I ended up buying an oscillating spindle sander at Menard’s.  With a guide board clamped to the table, it lets me feed the strips in and sand them down to a nice consistent .093″ thickness.  It’s really slow going to try to do it all in one pass, so I set up a second guide board on the other side to knock them down about half way.  One pass on one side, then a second pass on the other side of the drum and I have what I need.  It still takes quite a bit of time.  I installed the second largest drum, 2″ in diameter, but I think I’ll re-set it up with the larger 3″ drum instead.  The higher speed of the drum surface may help to make it go a little faster, and the larger surface area might keep the drum from loading up or wearing out longer.  With the shop vacuum sucking dust out around the spindle there’s virtually no sanding dust floating around, so that’s nice.

I got four strips done before I knocked off for the day.  Doesn’t sound like much, but there was also a few hours of Pinewood Derby axle and wheel work in there, as well as some play time with the grandkids.  Oh, and I did groove a couple dozen more rib capstrips too.

Bending wood and building stuff

This morning I went out to check the epoxy on the bending form.  It’s not warm in the garage (low 50s), not ideal for curing epoxy.  In addition, I was not too precise in mixing the epoxy.  I have a small scale that weighs in grams, ounces or even carats that I plan to use for epoxy to be used when measuring epoxy for actual airplane parts, but I didn’t use that last night.  Anyway, the glue was hard but still a little tacky on the surface – so not totally cured but “OK enough” to use.  I pulled the three capstrips out of the water soak and clamped them in the form.  A few hours later they had taken a fairly good set — but one of them cracked at the peak of the bend.  Looking at that one, it would have been OK if I’d either bent the other end, or cut the slot on the opposite side.  I just happened to try to bend it in a direction that didn’t work well with the grain slope of that piece of wood.   I’ll have to watch that on future pieces.

Knowing that I’ll want to rip some 1/8″ thick strips to make the wingtip bows and the frames for the tail feathers, I went looking for a way to do that easily.  I’ve been successful in ripping thin strips on the table saw, but as countless others have discovered doing it between the blade and rip fence is not the safest way.  The blade tends to launch the cut strip backwards off the saw table.  I found this thin strip rip jig at Rockler.com, which looks to be exactly the tool I need to rip pieces for laminating.  It’s not expensive, and I can think of a dozen other projects for which it would be very useful to be able to make strips for curved laminations.  I ordered it.

At lunch time I pulled the strips out of the bending jig and installed the rest of the forming blocks on the rib jig.  As I thought, the bottom capstrips won’t need to be pre-bent.  So, the first rib jig is ready to go.

The next job will be to shave the 1/8″ x 3/8″ strips received from ACS down to 3/32″ thick.  They’re actually a little thicker than spec, around .135 or so.  I thought about setting up something to jig up my low end belt/disc sander to do the job, but I don’t see a lot of success there.  I have a razor plane, but it doesn’t seem to work well on the wide side of the spruce strips.  I will have to figure out a good way to shave or sand or plane these down to the right thickness.  I did cut out all of the geodetic braces for the first rib, and marked them according to their placement.  I’ll use them as patterns to cut the remainder — just as soon as I figure out how to get those strips pared down to the right thickness.  Sanding just the ends down is going to be too time consuming and the results would probably not be consistent enough to suit me.  I need to figure out the best way to shave about .040 to .045 off of those strips.

Finally — the first shipment of spruce!

The UPS man just delivered a 30# package of spruce capstrip from Aircraft Spruce.  I can now — finally — start building.

The first step was to set up the table saw to groove the top and bottom rib capstrips for the geodetic braces.  They need a 3/32 x 3/32 groove cut on one side.  Getting the saw set up to cut a perfectly centered groove was trivially easy, and it gave me a reason to install the zero clearance throat plate on the saw for the first time.  Not wanting to experiment on the expensive spruce, I cut a couple of strips of pine the exact size of the capstrip and used one to set up the saw for the right depth and spacing.  The strips are small enough that rather than trying to use a push stick to feed it all the way through, it works out best to feed most of it through in one direction and then flip the piece around and feed the other end in.  The saw is set up precisely enough that you can’t see where the transition is between the grooves cut from the two ends.  It’s perfect.  With that done I grooved a dozen pieces of capstrip and decided that would be good for a limited test run.

I’ll also need a bending jig for the capstrip, since the top piece needs a pretty good curve toward the leading edge.  I could really probably do it dry, but I’ll feel better knowing that the wood is less stressed during assembly.  Better to put the curve in beforehand, I think.  The spruce is flexible enough that I don’t think there will be a problem with the bottom pieces, but we’ll see how it works out.  I cut a bending fixture from a chunk of scrap 2×4 — it split on the end as I was finishing up the cut, so I figured what better time to mix up a spoonful of T-88 and epoxy it back together?  After all, the glue joint should be stronger than the wood itself.  We’ll test that out.  Once that glue cures and I get some capstrip soaked in water and bent, I will finally be able to finish blocking in the rib jig and start cutting the geodetics.  I’ll need to also set up some sort of rig to sand or plane the ends of those down to 3/32″.

The grandkids are coming over Saturday to get some help with their Pinewood Derby cars.  Looks like a full-on woodworking weekend.

More jig work and research

I did some additional work on the rib jig yesterday, including installing the main spar locating block and cleaning up a few nail points that were poking out the bottom.  I cut a bunch of blocks to locate the outer shape of the ribs, but did not install them yet.  I want to wait until I have some spruce stock to put in place, so I make sure it’s all in the right place.  I really want these to turn out as close to perfectly consistent as possible.  I had planned to use some pine cut down on the table saw to set up and test the jig, but it occurred to me that I had no way to know for sure my pine strips would be the exact same size as the capstrip stock supplied by Aircraft Spruce.  So, it’s time to order some wood.

Started rib jig #1

I spent some time yesterday working on the first wing rib jig.  The workbench needed a new top surface, so I picked up a sheet of 3/4″ MDF at Lowe’s.  They were nice enough to cut it for me.  I ended up with one piece 3′ x 8′ for the bench, and two 1′ x 4′ chunks for rib jigs.  Nice how that worked out.

I marked a center line on the MDF and laid out the rib setup from Sheet #1 of the plans over it, then trimmed the paper to fit the jig.  I hate cutting up plans, but there’s an extra copy of that page for this reason.  I made all of the little chunks of plywood for the locating blocks, and cut a few small pieces of pine stock as needed.  Then I cut out the places where I would need holes to accommodate clothespins, marked those on the MDF and cut them out with a scroll saw.  I used some spray adhesive to stick the plans down to the MDF.  So far so good.

Next I had to find some clear poly to cover the plans sheet.  I finally remembered the nearly 4′ long bag in which the plans were shipped; it fit just fine.  With that in place I started nailing the locating blocks in place over the plan sheet.  I got most of them done before knocking off for the night.  I still need to make one more plywood block for the main spar locator, and make the blocks for the top and bottom capstrips.  I haven’t decided for sure how to do those.  I had thought about using a couple pieces of pine bent to fit, but that seems like a great way to mess up the jig trying to get them perfectly in place, and the jig needs to be as close to perfect as I can make it.  I’ll probably go with closely spaced pine blocks, nailed in place.