Brief Description: Countersink 702 and 606 spars, scuff trim tab part
I did not get a lot done today but I learned some and also created another reason to order parts from Van’s. I had to do the machine countersinking in the E-606 trim spar and four holes on the left main elevator spar where the E-705 rib attaches. I knew I needed some way to keep the guide of the countersink cutter centered from my earlier experience with the training projects so I drilled a #40 hole into some MDF scrap then clapped it up so that I could slide the flange of the spar over the MDF and over the hole all matched up with the countersink cage in my drill press. Well the hole in the 705 and the aft facing part of the 606 went well but when I did the top flange holes it became very inconsistent.
I think the more I used the hole I drilled into the MDF the bigger it got and this allowed the bit to move a bit in each hole. As you can see this left me with some out of round holes, the one in photo 1 is the worst one of all. The others are not so bad, but there are enough of them and they get worse towards the root end of the spar that I have decided I will order a new part and try again. I will use a suggestion of backing up the holes with a strip of aluminum and drill and cleco them together this will make for a ridged pilot hole and I should not get the movement I was getting. As you can see from the last two photos I did do some of them correctly. These are the two holes that attach the 705 rib to the 606 spar. These holes are countersunk to be exactly flush since this is the top layer. The other holes in the top flange of the 606 get countersunk just a shy bit deeper from flush since the dimple in the skin will sit in there. I am going to check on VAF to see what other builders think; my guess is I will be told to use the part. I am normally one to take this advice but this spar is the only thing supporting about one third of the elevator and it gets the trim tab attached to it. I am guessing there will be a fair amount of stress on these parts.
