Wings 5.5, total 468.5 - Drilling wing spar nut plate holes begins

Feels good to hear the sound of the drill carving out aluminum holes again. Before I could do that, however, I had to perform those laundry list items I mentioned in my previous post.
-Marked the wing spar so that orientation is clearly marked so that front/rear/left/right/top and bottom are identified. I still need to write down the serial numbers that Van's stenciled into the spars as I am sure I will need these when I order the fuselage kit to get the matched center section.

- Took a piece of 1/8 inch thick x 1.5" x 3 foot long aluminum angle I purchased from HD a long time ago and clamped it flush to the inside edge of the bottom spar flange using my cleco clamps and some small bar clamps. I would recommend this size angle for this job because it sits nicely overthe rivet heads that attach the wing spar together. The 1/8 inch thick angle is what will provide the additional material that the countersink pilot can insert into as the countersink carves out the holes for the screws and the nut plate rivets.

Note that upper and lower spar bars on the underside of the above picture only go about 1/3 of the way down the length of the spar, making it a bit awkward to sit on the bench with the bars facing down and the flanges facing up. The next step was to clamp the spar to the workbench so that it won't move while applying pressure on the drill to drill through the spar flange as well as the thicker angle on the back side of the flange. I placed some additional blocks of wood under the spar web about half way down the spar beyond the length of the spar bars to help level the spar on the bench. I then used my larger bar clamps and more wood blocks to secure the spar to the bench.

Then there was nothing left to do but start drilling some holes. I started on the bottom flange after taping the crevace between the spar bars and the spar flange to avoid getting small aluminum chips stuck in there. I chose to start with the #40 holes for the rivets for each nut plate, since I was still mulling over just exactly how to drill the center holes to ensure the countersinks were set correctly. Having a 3 foot long piece of angle allowed me to simply drill all the rivet holes and cleco them in place as I went. I was able to cover most of the nut plate rivet holes on one flange.

Then came a moment of pause and deep thought. Originally I said I was going to mark the center hole location with a sharpee and then remove the angle and try to locate the center point for a #30 hole. I then though back to what Dan said on his site - that he used a number 21 countersink bit instead of the #30, which has a pilot that more closely matches the diameter of the prepunched hole in the spar flange. I then further realized that this hole thing about using the #30 countersink was based on Vans recommended method of clecoing the nut plate onto the spar flange and then using that #30 countersink whose pilot would fit inside the nut plate hole just about right.

Since I am not going to cleco the nut plate to the spar flange, the whole idea of using a #30 countersink bit kind of goes right out the window. It makes absolutely no sense to try to use a countersink bit that has a pilot that is smaller than the diameter of the hole that is needed for the screw that will ultimately have to go in there. In fact, the prepunched center hole seems to be about the size of a #22 drill bit.

So I shifted my plans just a bit. The plan now is to follow Dan's lead and the info on my drill guide chart from Cleaveland Tools and use a #21 drill bit to drill the center hole through the spar flange and the aluminum angle for each nut plate location, followed by  a #19 drill bit and a  #19 countersink bit. This should keep the countersink pilot exactly where it needs to be to ensure that they turn out correctly.

My drill chart from Cleaveland tools shows that an AN509 R8 screw should be predrilled and clecoed using a #21 hole initially, followed by drilling a #19 hole and countersink for the proper clearance to insert the screw. I did get both drill bits and the #19 countersink bit in my tool kit, so this should be easy work for tomorrow. (*Ed note - I previously wrote that I did not have a #19 countersink bit, but I checked again as I put the cars in the garage and closed up the factory for the evening, and found that I actually DID have a #19 countersink bit in my arsenal of cutting tools, so Cleaveland Tools rocks yet again. Had I realized that earlier, I might have drilled a few countersinks, but oh well.....)

These last pics are of the rivet holes drilled and clecoed. Note that the last pic shows a set of holes that are at opposing angles to each other near the root of the spar. This is because this is the area where a series of about 4 ribs are installed very close together which is the wing walk area where everyone will be stepping on the wing to enter and exit the plane someday. As such, there is not enough room to install these nut plates in the same linear fashion as the others, so that is the reason that they are angled.

I also scheduled my Tech Counselor visit with John Linz this Thursday evening to inspect the work I did on all the empennage parts. Sure hope that goes well. John lives just a mile or so up the street from me, and he told me over the phone that I must be the closest tech counselor visit he has ever made. What can I say, EAA folks just seem to naturally congregate together, and the EAA/RV community seems to be growing in this area, which is a great thing.