January 19, 2010

Roll Bar Assembly - continued - 2.5 hrs.

Today I continued my work on the roll bar assembly, or cabin frame. In looking around for some examples and ideas of the best way to proceed, I decided to follow the method used by my friend, Mike Bullock. He documents this method so well on his website, that I probably won't repeat with dozens of pictures here. The idea is to clamp the F-631A channels to a solid flat surface for assembling and drilling. So I stopped by a local supplier and picked up a couple of scrap pieces of 1/2" waferboard to use to make a jig. I nailed them together to form a 1" thick solid flat work surface, then roughly cut it to the shape of the bow. You need something you can clamp to and drill into that will hold the assembly perfectly flat.

Next, I looked around and found a piece of aluminum channel to use along the bottom edge as a straightedge. You could also use a piece of aluminum or steel angle here. This ended up working just fine. Next, you can't see them in the picture above, but I screwed two small aluminum angle pieces into the jig one on the left and another one on the right, measured exactly 42-5/32" apart. These function as stops to hold the bottom ends of the channels a precise distance apart. This is the distance called for in the plans, but you need to measure across the fuselage to make sure. You can imagine my delight when I stretched a tape measure across the fuselage and measured. EXACTLY 42-5/32" across (allowing for the thickness of the two brackets). Once again, the quality and precision of the Vans Aircraft kit has really impressed me! So the purpose of this jig is to hold the two channel pieces perfectly flat and exactly this distance apart. So I butted the ends of the channels against the angle pieces and clamped them down as seen above. Then you measure the height at the top of the bow. The plans call for a height of 17-19/32". Mine was way too high at first. So I had to do some careful filing to bring the top ends of the channels together nice and straight, and reduce the height until it was just right. It took quite a few iterations, filing away a little at a time.

When I had the height and width exactly where it's supposed to be, I clamped the joint plate across the two ends of the channels, as seen above. Then it was drilled to #30 for all the holes, and clecoed in place.

Next, I need to do the layout for all the rivet holes that will hold the straps in place. I'll tackle that next time.

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