An M.G. Locost Build
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November 28, 2011
The Nose Jig

All of the suspension pieces are done. Cut, ground, filed, and finished. Every last one. Oddly, we're no longer in such a big hurry to get them all welded together. In our experience, it's not a bad idea to let the memory of all that work fade away before subjecting anything to the torch. Welding is more or less permanent, the ďlessĒ part involving making new pieces, something we donít want to have to think about for a while.

  Best Locost nose jig ever
click to enlarge

So this past weekend we made a jig for the nose. This is not just any Locost nose jig, this is the mother of all Locost nose jigs. It locks everything in place so you can weld from any angle, itís precise to within 0.01", and it allows for shimming, which means we can get the space between the upper and lower tubes to be precisely 11". The nose is very likely the single most important part of the frame to get just right, because it locates half of the front suspension. Of course we realize a fancy nose jig is probably overkill, but this is nothing. It'll get worse.

We already had the upper and lower tubes for the nose cut and ready to go, but the side tubes we originally cut last August turned out to be oddly misshapen, the end angles not really matching anything on the jig. So we cut a couple more tubes, and ground and filed one of them down until it was too short, and then cut another one. After almost as much filing and trial fitting as the A-arm tubes required, we finally had one tube with perfect angles, and only about 1/16Ē too long, easy enough to file down to the precise length. One thing bothered us, though.

LB tube no longer square  
click to enlarge

The end of our freshly-filed side tube didnít seem to fit squarely on the bottom tube. It was perfectly flush, but when we positioned it with the forward face perpendicular to the frame, the side of the tube wasnít lined up with the frame lengthwise. That didnít make sense. Stand a square tube on a flat surface and the section it makes on the surface is a square. Lean the tube backwards and the section will elongate into a rectangle. Then lean it to the side, and the rectangle should once again elongate to that side and start to become square again.

But noooo. As anyone with an advanced degree in Euclidean geometry would tell you, the new shape is not a square, but rather a diamond, with obtuse angles on two of the corners and pointy angles (the opposite of obtuseóacute?) on the other two. Sounds crazy, I know, but that's simply how the universe works, apparently. So because of that itís impossible to get the side nose tubes to line up with the frame in both the longitudinal and crosswise (lateral?) directions.

So not such a big deal. The only critical angle is longitudinal, because the suspension brackets are welded flat on the side of the tubes and have to line up with each other in the same plane. Which means the forward face of the tubes wonít be square with the frame, but will instead be angled back slightly. Which isnít a problem except for the fact that our beautiful new jig and the one perfect tube weíd made so far require the forward face of the tubes to be flat. So we were stuck. We had to sleep on that one.

In the morning we got out the Dremel and the hand files and set about modifying the jig. Good thing our one perfect side tube was a bit long, since it had to be re-filed on both ends for the slight rotation of the tube. Geometry was never our favorite subject, but we could imagine that rotating the bottom of the tube so the sides were lined up with the frame would rotate the top of the tube back and toward the center of the nose. Which meant we needed to file the bottom front and outside edges of the tube. Incredibly, that worked. The tube was now lined up and as a bonus was also the perfect length. Getting the second tube to fit was a piece of cake.

  Mock-up nose with fudged brackets
click to enlarge

Interestingly, we ran into this exact same problem on the mock-up frame five years ago, but we attributed it to poorly made wooden tubes, i.e. tubes that werenít quite square. Back then we angled the side tubes so they were square with the front of the frame. Which meant they werenít square on the side, and so the suspension brackets didnít line up. But that was okay because we were big into fudging back then. And it was wood. So thatís minus 1 for experience gained from building the mock-up frame.


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