Wing Spars

After marking the spars to determine all of the correct orientations, I layed a strip of tape along all of the joints.  I did not want to get metal shavings into the crevices, as I feared they might work there way into the metal:

After countersinking all of the rivet holes, I began the process of c-sinking the nutplate screw holes.  I built a small jig out of aluminum angle to keep the c-sink pilot centered.  Process was 1) cleco jig to nutplate rivet holes, 2) use side-grip cleco on the edges to hold it in place, then 3) remove the rivet hole clecos to provide room for the c-sink cage.  Jig looks as follows:

I then started c-sinking...the instruction manual says to dimple a piece of .032 to #8 screw to use as a test sample to determine when the screw hole is countersunk enough.  I have a lot of concerns here, as it appears you have to remove a great deal of material to get the skin to lay flush...I need to check with the list before proceeding (click pic to enlarge):

You can see that the c-sink has long since bottomed out and the hole is enlarged.  I am using a #30 c-sink per the instructions, and it appears that the skin is not quite even flush.

What I found out was that the skin will never sit perfectly flush without the screws "sucking" it in.  I was actually c-sinking past the diamter of the countersink.  I ended up backing off a bit on the depth, and the skin still sits as flush as the overdone hole.  The picture on the left shows the hole that was too deep....the picture on the right shows the good hole:

If I find out at a later time that they need to go deeper, I can still do so even with the nutplates attached (even though I don't think it will be required).

Lots more countersinking for the inspection plates and spar root nutplates.  You will be very sick of attaching nutplates by the time you are done with the spar.