Spars in thar.

It took a while, but I'm finally at a place where I was able to pull those beautiful Sitka Spruce boards down from the wall and make some sawdust. I had two wide 13' boards, three narrower boards at 13', and a few 6' boards for the ailerons.
The two widest 13' boards became forward spars. The two nicest of the narrower boards became the rear spars. The last of them was ripped into two 3/4" square sticks to make the leading edge.
Both front and rear spars were then ripped down on the table saw just a little wider than final width with the required bevel on the top edge. The spars were then hand-planed to final size. A chop-saw squared up the root-end of the spar stock to have a square edge for laying out holes for hardware and the taper at the wingtip.


Spar marked and ready for drilling. Hole for Wingtip bow already cut.

All holes were drilled with my little bench top drill press. The spars laid across my new sawhorses which were adjusted to keep the spars square to the drill. I made sure to drill into a piece of plywood behind the spar to prevent tear-out.

Drilling holes for the strut attach brackets.

Wingtip tapers and bow cutouts

A 3/4" hole was drilled for where the wingtip bow will mount and then the wingtip taper was cut into all four spars as marked earlier.

Once the bevels were cut, holes all drilled, and tapers added it was time to add the strut-mount doubler plates.

There are three sets of two plates on the forward spar and two sets on the rear. These plates are made of 1/8" plywood and help to distribute the loads from hardware attachment bolts along the spar. Only the center plates can get installed for now as they protrude from the spar and would keep the ribs from sliding on if they were epoxied on before the ribs. Since all the holes are already drilled in the spar, I can only glue the plates on one face of the spars at a time. Once cured I come back, drill though the existing holes in the spar through the doubler plate. Then I can go back and epoxy the plates on the second face and repeat the drilling from the other side.

This is where I made a mistake. I didn't have the 1/2" aircraft nails needed to hold the doubler plates in place while the epoxy set, but in an effort to make progress I elected to use the 1/4" nails I had. The first round of gluing, attaching the plates went well, the holes were drilled, and the second set of plates was glued on. Unfortunately these plates were a little more warped than the first set and the 1/4" nails weren't enough to hold them in place as the epoxy set, but did hold long enough for me to go to bed thinking all was well. When I came back the epoxy had cured out, but the corners of both plates on the rear spars had lifted. The only fix was replacement.

I went in with a set of pliers and pulled out all the short nails, then took my wood plane and shaved the plywood down layer by layer until only a veneer of epoxy was left on the spar. A sharp scraper made short work of removing the epoxy. Then I had to wait for more 1/8" plywood and the correct nails to arrive from Aircraft Spruce. New plates were cut and glued onto the spars, then drilled to match the old holes.
Total time lost in the repair: 4 hours.