Finished match drilling the lower J-stiffeners after repositioning them on the upper flange. Deburred all the holes and set the stiffeners aside for later in the build.
All rivet holes for the nutplates were countersinked and the rivet holes for the ribs common to the upper flange. I also treated the C/S surface for the latter holes with Bonderite.
I started to think about how to control the wandering of the C/S bit in the hole. The plans say to install the nutplates first, then do the C/S. The problem is the recommended #30 pilot is a bit smaller than the nutplate screw hole and the bit wanders giving me this horrible chattering. I have no idea how other builders got good countersinks following the plans.
I'm going to fabricate a backing plate that attaches to the inside of the flange and I can cleco in place with a tight #30 hole to give the CS bit something to steady it. You can see in the 3rd picture the lower hole without the backing plate. The upper hole doesn't have any chatter and gave me a very polished CS surface. This approach looks promising. I'll fabricate the plate to cover at least three screw holes since I can't have a cleco in the nutplate rivet holes next to the screw hole I'm working on.
If this works, then I'll have to drill out all of the nutplates on the LH spar.
Finish match drilling the lower J stiffeners on the upper flange
First attempt on the actual spar. This is not full size yet, so it's fixable
Test panel to figure out how to get good countersinks for the #8 screw holes
