Saturday, November 20, 2010

The practice fuel tank

I've taken to referring to the map box as "the practice fuel tank." Obviously I have no direct experience with building the fuel tank, but I've certainly read a lot about it and to all reports it is a task fraught with peril, frustration, and many instances of abject failure. In fact, there are those that have detected a business opportunity inherent if the difficulty of building a non-leaking fuel tank and are offering a guaranteed build of a fuel-tight tank, for a price.

The map box is not nearly as critical as the fuel tank, but for the mundane, utilitarian function it performs it has been relatively obnoxious to build.

Back at the beginning of the job, a measurement was provided for finding the location for the 1/4" hole that will go through the door to provide a home for the camloc fastener that will latch the door in the closed position. Unfortunately, that measurement used the bottom of the door as a reference and I have since shaved some unknown amount of material off of there. A measurement from the top would have worked better. Alas, the damage is done and the ambiguity immutably created. Helpfully, though, the 1/4" hole is in line with the existing rivet holes in the control panel to which the box will be mounted.

All I needed to do was find and mark a point in the center of the two central rivet holes.

That was, uncharacteristically, as easily done as said. Leveraging knowledge gained from recent experience with drilling 1/4" holes, I knew to start with a #40 pilot hole. Very characteristically, that was easier said than done. Just as the bit broke through the front of the map door, it exploded.

I calmly cleaned up that mess and pressed on. "Calmly" in this instance is, as you can probably guess, slang for "swearing with the great proficiency gained though a year of airplane building." In any event, that's why I try to always have a spare #40 bit on hand.

That put a nice, perfectly centered hole through the control panel and the map box door, but didn't create the matching hole that was needed in the map box flange. To do that, I could only cleco in the side flanges of the map box because any clecos on the top flange would keep the parts from sitting flush. To keep everything in alignment while I drilled the flange hole, I added some clecos to the flanges of the box halves.

The hole in the door is finished at 1/4", but the remainder of the holes behind it need to be increased to 7/16" to allow for the width of the back part of the camloc. Sadly, my drill only goes to 6/16".

Good thing I have unibits!

A quick test fit shows that it's all going to work.

The camloc thingy has a couple of holes for rivets; those would have to be drilled through the panel. I used a center punch to mark them.

More clecos were useful for getting the box halves to align for riveting.

I riveted it all together, then tried to install the star washer that holds the outside portion of the camloc in place. The plans suggest using a small socket and a pair of channel lock pliers. That's a great suggestion, or would have been if my channel lock pliers hadn't fallen victim to a tool dispersion problem. They were at home. I was not. I tried just pushing the camloc against the socket with the socket placed between the panel and the door.

That worked, but only to a degree. To get the washer completely flush, I had to walk down a few hangars to borrow a pair of channel locks from Al the Tool Junky.

It's never too early to start dreaming of the day....

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