Sat Oct 14 2006

Countersinking wing spars

Since it was time to start on the wings, I unpacked the instructions from the roll they came in. They were pretty curled up making it a pain to handle. I thought I'd try ironing them to see if I could flatten 'em out.

Using low heat and no steam worked great. :-)

My dad was in town for a visit, so I had prepped the shop area and mounted the wing jig beams. I'm planning on working on both wings simultaneously, so there's 2 sets of beams. The beam on the right in the foreground was going to come right up into an HVAC duct, so I had to chop it short and offset it in order to attach it to the floor truss above.

We countersunk for all the tank attach screws. Using a piece of 1 1/4" x 1/4" x 6" long aluminum bar, we'd align the pilot hole with the the prepunched hole using the back of a drill bit. Then the countersink would still have a pilot to center on even after the countersink enlarged the hole.

My countersink cutter for the screws is the three-flute variety. This kind is way more prone to chatter than the single flute ones. I got a little chatter on some holes, but they all cleaned up...except for this one. The bit chattered so badly that it moved my pilot bar around. Maybe I should've used stronger clamps. In retrospect I'd probably buy a different countersink cutter. The X on the one nutplate rivet indicated one that needed replaced. I only had a few of those...got 'em drilled out and replaced. Now they all look good.

Update: I talked to Bruce at Van's about this countersunk hole. He looked at the photo and said there was no structural problem here. He suggested that I might not want to tighten this particular tank attach screw down all the way to avoid puckering the tank skin.