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F-605C doubler positioning tip


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This piece forms part of the receptacle for the aft wing spar. It comes pre-bent, and the builder tapers the end of it, putting a 1/4" radius on the pointy end.

Several holes are drilled in this piece...drilled in assembly with the F705A bulkhead piece., including one in the middle of that 1/4" radiused end. What this means is that if you don't have it clamped on exactly right, the hole could very easily wind up a bit too close to the edge. I know this for the obvious reason.

Also, one of the other holes on the piece has a fairly critical placement...right next to one of the bends. So proper location of this piece prior to drilling is absolutely essential.

Hindsight being the amazingly clear thing it is, we realized that what SHOULD have been done was that the hole location on that pointy end should either have been center punched or had a pilot hole drilled in it. Then the piece could have been clamped in place with that positive mark (more precise than a Sharpie mark) centered in the matching hole in the bulkhead, and drilled out. This would then have been used as a fixed reference point, clecoed in place, so that the 605C could be easily aligned and drilled in exactly the right place.

Or, better yet, drill the pilot hole big enough to accept a cleco. Once the other holes are drilled, go back and redrill the pointy end to full size.

Perhaps this tidbit will help someone avoid the mistake we made.
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Thanks to all the warnings on the major builder Web sites about this, I've started changing the way I do doubler bars like this. I create the tapers AFTER I've done the drilling. This includes the radius (usually 1/4") ends. This way, it's fairly impossible to violate any edge distance problems.