Wednesday April 7, 2021
Cabin Frame Roll Bar (Cabin Frame)
1.8 Hours

I started out tonight by drilling the holes through the F-631E splice plates using the lines I drew last night.

I drilled through both of them at once to save time.

Then I cleco'd the F-774 skin in place so I could get a good idea of where the roll bar intersects with the fuselage. I then re-measured my fuselage to ensure it's close to the Van's measurement, which it is.

Then, I verified that my work bench is still flat (it is) and that the edge is straight (it is) and clamped the aft F-631A channels in place. I measured the width, compared to the desired width, and determined that I needed to trim about 1/4" from each one.

I trimmed the channels with the belt sander until I was happy with the width and height dimensions. Then, I turned my workbench into a jig by screwing small wood blocks to it in the right dimensions.

With the channels in the jig, they are constrained to the right dimensions.

It took some time and fiddling to get it right, but now I don't have to worry about the dimensions drifting while I assemble the roll bar. I read on VAF that some people have actually had the rollbar shrink during riveting, so I put blocks on both the outer and inner edges.

The next step will be to drill one of the F-631E splice plates to join the two aft channels.

This will be a point of no return, though, so it's a good place to stop for the night. I'll come back to it next time and re-check all of the dimensions before I drill anything.

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