Saturday, April 10, 2010

A tough day

With the 71 - 73 matched holes drilled, the piece of aluminum (the F-1204D AFT BULKHEAD for those of without a program) gets removed and all of the new holes need to be duburred. That doesn't take long, although the holes on the inside edge of the center section have to be deburred by hand - the deburr bit that I use in my drill won't fit in there.

I considered quitting for the night after finishing that up because it hadn't been a terribly good day. In fact, it had been a rotten day. It was one of those days that everything I touch breaks, falls down, gets riven asunder by abnormally potent paranormal forces, or, as in the case at work, doesn't function correctly because I was in a hurry to get it done before leaving for vacation and did it very stupidly. Seriously, how distracted do you need to be to create a database distinctly for the purpose of supporting an automated report emailing system for the corporate bigwigs but neglect to actually put in a column to store email addresses?

Yeah, it was that kind of day.

After the holes are drilled and deburred, the bulkhead and a few other little pieces get riveted to the center section. The different holes require different rivets in different locations, so I marked the type of rivet to be used for each hole directly onto the bulkhead to avoid mistakes:

Some of the holes across the top are filled with AN470 style rivets (round head on top), but others take the AN426 flush head rivet. You know flush rivets are coming when you're instructed to machine countersink certain holes. The directions weren't super specific about which side of the center section was to be countersunk, but since the very next sentence has us dimpling the same holes in the bulkhead that is to be riveted on, it was pretty obvious that it was the outside of the center section that was to be countersunk.

What wasn't quite as obvious immediately was why there was a tolerance (.2544 - .2566, going from memory) provided for the diameter of the outer rim of the countersunk hole. Usually you just countersink far enough that the rivet sits flush. It didn't take me long to realize that it was to provide room for the inside of the dimpled skin to fit. I have a nice piece of sheet metal that Ted loaned me that has various sized holes drilled into it, so I just used the 1/4" hole to gauge the correct size of the coutersunk holes.

I'm not sure why only those holes get flush riveted in the first place, as opposed to the entire top row being flush riveted, but I'm guessing it is because that portion of the bulkhead with be very close to the edge of the fuel tank. Round head rivets could work against the side of the fuel tank and cause leaks. That's my guess, anyway. I'll find out for sure someday.

With the skin dimpled and the center section underneath the skin countersunk, the rivets lie pretty flush:

Those are just sitting in there, not yet squeezed. There are a few little parts that need to be prepped an riveted onto the assembly at the same time. I'm not in any huge hurry - last time I squeezed that many AD4 sized rivets I gave myself a third eye in my forehead when the rivet squeezer flew back and whacked me. That's the kind of thing that you remember for awhile!

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