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Log Entries for Ribs

Log Entry Date: Jan 29, 2012


Make bending and backing blocks
Time to cut the form blocks that will be used to bend the ribs to their final shapes. I took the blocks that I lovingly created using photocopies earlier and ran them through the band saw. Then I used the bending form blocks as a guide to create a backing block. I traced the outline of the bending block onto some MDF and then shifted the bending block and traced inside the original line on all sides about 1/4" (see picture). You cut the inside line so the backing block is about 1/4" in from the edge of the bending block. It doesn't have to be precise. For good measure I sanded the straight edges using another wonderful power tool Chris has in his basement.

OK, now for a word about how I'm going to bend these. Notice the picture of the aileron nose rib with its backing block. Using a 1 7/8" paddle bit I counter sunk the hole in the bending block so I could run a 1 1/2" long 3/16" diameter machine screw through it. Then I put a washer and nut on the INSIDE of the bending block. In other words, on the side where the aluminum rib will go. This effectively makes a "pin." When you're done making the block, the process for bending is very fast:

  1. Slide the rib over the 3/16" machine screws sticking out of the bending block.
  2. Slide the backing block onto the screws
  3. Clamp both blocks in a vice
  4. Whack away with a 2" dead blow hammer. Make sure that your first hit is at the base of the aluminum to set the radius nicely. Also, be sure to hit that little spot between the notches and that will help the tabs lie a little flatter. NOTE: The dead blow hammer is NOT a rubber hammer. The head is filled with lead shot or sand or something to give it weight and it doesn't bounce.
  5. Once you've got the initial radius set, just hammer the edges over.
  6. Lather, rinse, repeat.
Using the cut form block to trace the backing block lines roughly 1/4" in from the edge. NOTE: This picture shows an error. I missed cutting one section of the block. See Feb 3-4 entries for the error and the fix.
Sanding the straight edges.
Aileron rib bending block and backing block.

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