Page 20-03

[DonFromTX]

I am having trouble understanding the attachment of the center section assembly to the center section aft bulkhead. When you cleco the two pieces to the bottom skin, they will of course rock back and forth. A couple of 1/4 inch bolts initially set the position, but then it says to release the clamps and let it sort of self align! It "self aligns alright, to many different positions depending on how you hold your mouth! Of course after this casual instruction, you are to match drill 72 holes in what I suspect is a pricey center section assembly, and I would rather get it right the first time. Surely it must be more precise than that, right?

 

[rgmwa]

I am having trouble understanding the attachment of the center section assembly to the center section aft bulkhead. When you cleco the two pieces to the bottom skin, they will of course rock back and forth. A couple of 1/4 inch bolts initially set the position, but then it says to release the clamps and let it sort of self align! It "self aligns alright, to many different positions depending on how you hold your mouth! Of course after this casual instruction, you are to match drill 72 holes in what I suspect is a pricey center section assembly, and I would rather get it right the first time. Surely it must be more precise than that, right?

I think they mean that while the bolts set the correct height of F1204D, you may not have centred it exactly along the length of the channel when you first clamped it. Even though you may have managed to cleco the bottom skin to both bulkheads, loosening the clamps after clecoing F1204D to the bottom skin allows the bulkhead to move sideways slightly if necessary to take out any misalignment.

I carefully marked the centre of F1204D and the channel and lined them up before clamping. When I laid the bottom skin in place, all the holes matched up perfectly in both bulkheads.

 

[Mich48041]

Drill holes perpendicular

Drilled holes should be perpendicular to the heavy center section channel. Some builders make a drill guide from a wooden block with a hole in it that was drilled on a drill press.
Joe

 

[DonFromTX]

I got to thinking though, if the alignment is off even a little bit, the side skin holes will not be aligned with those parts. Big trouble down the line. Perhaps I should cleco the side skin on in order to be sure of the position when drilling the holes..

 

[rgmwa]

I got to thinking though, if the alignment is off even a little bit, the side skin holes will not be aligned with those parts. Big trouble down the line. Perhaps I should cleco the side skin on in order to be sure of the position when drilling the holes..

When in doubt, follow the instructions
You actually do need to fit the side skins later to match drill some holes in another part, but I don't think you need them for this step.