Tag: Glue

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Bending more capstrip, and glue efficiency

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.

 

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Fixing up the steamer

I built two more ribs last night and took them out this morning; I’m up to 14 now.  I’m trying to 3D print some clamps too use on one of the jigs that has locating blocks too thick to use the small red sprig clamps I bought.  of course first I have to fix the 3D printer…

When I used the steam box, the door warped — no, curled outward.  I flattened it out, but because everything isn’t perfectly square it really only fits on one way so I can’t just flip it over.  Tonight I cut a couple of 3/4″ square stiffeners and epoxied them to the outside of the door.  I need to bend some more pieces of capstrip, and I can’t do that until the door is usable.  We’ll see if this is enough or not, should be interesting at least.

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Fixin’ and cookin’ ribs

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.

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A little setback

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.

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Second jig built

Yesterday I did a little shop cleanup.  Not a lot, just enough to get done what I wanted to do.  I cut a length of 3/4″ x 3/4″ pine and cut a bunch of 1-1/2″ blocks for the second rib jig.  I got the work bench partially cleared off.  The box from the R/C Cub went underneath, and the plans sheet and wings were moved to one end of the bench.  I now have roughly half the bench covered by model airplane wings, while the other half is being used to build the real thing.  ‘Murica, as my kids would say.

So, I built the second wing rib jig.  I used the first rib from the first jig and blocked everything up.  I used some plastic sheet Lisa had picked up underneath it to prevent the glue sticking things together.  When it was all finished, I mixed up 20cc of epoxy and glued up two ribs.  That’s going to work as long as it stays cold, but the glue was gelling by the time I was finished.  If it warms up at all there won’t be time to do two at a time, unless I can find a way to pre-glue the capstrip grooves a lot faster.  I wonder if thinning out a portion of the T-88 and brushing it into the grooves would work.  For that matter, I wonder if pre-gluing the grooves is even necessary.

This morning I pulled both ribs from the jigs.  You can’t tell them apart, and you can’t tell them from the other four I had done.  Any differences between the six ribs I have done are slight enough they can be removed by sanding.  So, now I can double my production rate.

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More ribs

Rib #2 matches rib #1 to within plus or minus a millimeter or two everywhere.  I spent some time with an X-Acto knife and sanding block cleaning the excess epoxy off of the first rib, so it’s looking pretty good now.  Tonight I put #3 in the jig and glued it.

I was planning to make the second jig tonight also, but that’s going to just have to wait a little while.  The garage is getting too cluttered to work in.  I’ve got numerous tasks partially completed, and it’s a real mess.

  • I need to finish grooving the capstrips, first off, so I can use the table saw for other things. (done!)
  • I need to get the rest of the geodetic stock shaved down to final size.  I got my strip cutting jig from Rockler today, so we’ll see if the table saw can be used to help with that or not.
  • I need to cut more wood blocks for the jig.  With the spindle sander, I can make sure they are perfectly square. (done!)
  • There is some cleanup to be done, including two workbenches that are piled high with so much crap that I’m working with a rib building jig hanging over the sides on one end of the bench.  It’s an eight foot long bench and I’m using less than a foot of it.  Ridiculous.
  • I will need a place to store these ribs so they don’t get damaged.  And I definitely have to find a better solution for the geodetic braces.  The paper cups I have been using were a terrible idea.  They take up enough room that they’re a pain in the ass to use, and they tip over, fall off the bench and spill parts everywhere at the slightest bump or touch.
  • I have the table saw and spindle sander sitting halfway out in the middle of the floor, need to get a permanent location figured out.

That will at least get me to where I need to be to keep building ribs.  At some point I’m going to need another eight feet of workbench, but that can wait until I have the ribs and tail feathers built.  Pretty sure I can do all that on the 3 x 8 that I have now.

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#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…

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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.  🙂