Thursday, June 17, 2010

Sink, Counter-Sink

The idea of starting a new section of the fuselage seemed like it would bring with it some kind of change. New parts, new and exciting stuff to do. Well, not so much. The first steps of Section 22 are countersinking holes and riveting nutplates into place. And not just a little countersinking, either. Lot's and lot's of countersinking!

And that was just fine with me. I only had a brief amount of time available to work on the plane tonight and countersinking a passel of holes was just the right size job. It started out kind of tricky - step 1 offered the not so rare opportunity to easily dimple the wrong side of the part. The dimpling was only two holes, just enough to support one single, lonely nutplate on the lower firewall. I took a great deal of time making sure that I got the dimples on the correct side of the firewall. Once I had it figured out, I was taking no chances on forgetting.

Step 2 was much easier, at first. Both the "sloped upper flanges of the tunnel ribs" and the "nutplate attach holes in the fwd fuse skin" were easy to find. It was the last part of step two that caused me so much trouble. Here, read it for yourself:

The sentence in question (or, more aptly, the sentence that caused the question) says, "Machine countersink the upper most hole in the F-1288 Cooler Stiffener." Well and good, that, but not nearly enough. You see, the hole in that part is being countersunk so that the part will sit flush against the firewall when it is riveted in place. The holes in the firewall underneath the part are already dimpled with Van's now-you-see-it-now-you-don't dimpling machine. They only pull it out on rare occasions; pedestrian tasks such as dimpling are nearly always left to yours truly. Anyway, the problem is that they did not dimple only one hole under the Cooler Stiffener. They dimpled, as even the most casual inspection will show, no less than seven holes under the Cooler Stiffener. Countersinking just one of the seven seemed like it simply would not be sufficient to allow the Stiffener to snug down flush against the firewall. It's always possible that Van's has posted a revision to a page, but a check of their web site showed nothing newer than Revision 2, the very version I was looking at.

This, in a word, was a dilemma.

I looked ahead to see if the countersinking was addressed later. It was not. In fact, in just a few more steps the stiffener gets riveted into place.

Usually the best thing to do when faced with a situation like this is to not do anything you weren't told to do. In this case, though, I can't believe that those holes weren't intended to be countersunk. I went ahead and did them.

The rest of the countersinking was easy.

Step 4 wants the Engine Mount Brackets to be clecoed into place and match drilled. I went ahead and clecoed them in, but the match drilling will have to wait. Thursday is my tiredest day of the week and I had reached my limit.

1 comment:

Kevin said...

aaand five years later the last sentence in Step 2 still hasn't been fixed.

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