Day: March 12, 2017

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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.