The Murphy Builders Site

Craig,
I just looked at the pictures of your fin that you posted, and it reminded me that MAM wants you to layout and build the framework on top of one skin. I found this to be a really bad idea when I was building the tailfeathers. Instead, I drew out where the framework should go on my work table and built it flat on the table I used small pieces of wood screwed right to the table as clamps and jigs to hold everything in place while drilling all the brackets. Worked great for me. I can see how you got in trouble trying to build on top of that potato chip of a skin. Just build it flat on the table.
Jesse

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Craig,
If you try to flatten the creases the holes will move apart from each other in the direction perpendicular to the crease. That will move them out of alignment with the ribs.

If you elect a new skin there are several ways to transfer the holes. In any case cleco as you go, start at the leading edge, and do one side and then the other back to the rear spar. Be sure to get a proper start at the leading edge with the first holes correct as you can't recover if wrong.

Method #1
Use a long strap hole finder of the type that puts a pin in the existing hole and allows a spot drill start on the new skin. Do not drill into the hole finder. After spotting you can remove the hole finder and drill through.

Method #2
This can be used where the hole finder reach is insufficient. There are small "buttons" with a #30 (or #40) pin on one side and a short but sharp point on the other. The pin is inserted in the hole to be copied, new sheet positioned on top and a LIGHT tap on the new skin will leave a drill place mark on the under side of the new skin which is then drilled out. It might be useful to put some layout blue on the new skin to show up drill locations better. Support under the rib during tapping would be good if accessible.

Method #3
To replace #3, you might be able to back drill the holes nearest the leading edge with a small right angle drill.

In any case, good luck. We have all remade parts, in some cases several times although those persons shall remain anonymous.
Ralph Baker



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