Wing Main Spar 13-3-8, 13-4-1 to 13-4-9

There's a little more work to be done on the main spars, and this starts with reaming and countersinking the nutplate and 1/8" rivet holes at the inboard ends of both spars.

Countersinking was straightforward other than the two fuel tank attach nutplate holes closest to the step bars. I used a countersink cutter without a cage to slowly drill these to the required depth. I also had to be careful to make sure I countersunk on the correct side of the spar web as outlined in the plans

Using a countersink cutter without cage to slowly drill the two holes closest to the step bars

Wing attach nutplate and 1/8 rivet holes countersunk on the aft side of the spar web

Fuel tank attach nutplate holes countersunk on the forward side of the spar web

Next I continued with fabricating the tie down brackets. I had previously tapped the tie down hole, cut the brackets to size, and drilled a pilot hole. Using the pilot hole, I clecoed the bracket to the spar and then match drilled the #30 and #12 holes into the tie down bracket.

Tie down bracket clecoed and clamped to the spar, ready for match drilling

Holes were match drilled from the spar web into the tie down bracket, clecoing holes as each one was done

Next I removed the tie down bracket from the spar, deburred all drilled holes and clamped the bracket into my vise. Using a #8 nutplate drill jig I drilled out nutplate attach holes around each of the #12 holes as directed in the plans (be sure to not drill holes around the #12 holes closest to the end of the bracket).

I then countersunk the nutplate holes on the aft side of the bracket for flush rivets.

Using a nutplate drill jig to accurately place nutplate holes on the tie down brackets

Wing tie down brackets drilled, deburred and ready for priming

Next up I used a ScotchBrite pad to scuff the countersunk holes in the main spars in preparation for priming. This also did a great job of smoothing out the inside edges of the countersunk screw holes, so I did not need to use my fine needle file as previously thought.

I then primed all the countersunk holes and flange edges of the main spars using foam-tipped swabs to apply the EkoPrime. This worked well and I was quickly able to apply a thin even coat of primer around each hole.