An M.G. Locost Build
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May 7, 2012
First Welding Setback

Okay, Houston, it looks we've had our one glitch for this mission. We set the rear axle into the frame yesterday, and it didn't go so well. With all the rear tubes in place, installing the axle turned out to be at least as difficult as it looks, because the brake drums barely fit between the K and X tubes, and the differential only fits if the nose is pointing straight up, which it doesn't want to do in a normal gravitational field. But this wasn't the problem, and we eventually got the axle in, although not without a lot of banging around. I can already tell that installing this part after everything is freshly painted is going to be disappointing.

  Almost magic that it fits at all
click to enlarge

But the axle looked great in the steel frame, and we were pretty excited about it until we got out the tape measure. With the axle resting comfortably on wood blocks, not touching the frame anywhere, we adjusted the frame until the nose of the differential was centered and had enough clearance to move up and down easily. Still exciting, until we measured the distance from the axle to the M tubes. Too long, by about 2". So to reduce this we slid the frame back until the differential housing clanged loudly against the frame. I remember thinking at the time, that can't be good.

It wasn't. I thought we had a handle on all the dimensions of our donor hardware. Apparently not. Next time, we'll measure the rear axle with a ruler instead of just eyeballing it. In our defense, the book says to build a 5" wide slot in the rear bulkhead for the differential case, and we went with 6". So naturally you'd expect us to have plenty of clearance. And we do. On the right side. Is it really our fault that the case is not symmetrical? Of course we could've figured all this out earlier, before everything was all welded up, but I don't think there's any doubt in anyone's mind by now that that's not how we do things here.

It takes a certain attitude to do this  
click to enlarge

So we had a problem, and our options were limited to two: Lengthen the wheelbase or dig out the hacksaw and remove the errant tubes. Actually, in our case failure was also an option, but we chose the hacksaw because a longer wheelbase would look silly and have detrimental effects on ride and handling, which real engineers could probably tell you about. As it turned out, cutting away the offending tube took only a few minutes, and cleaning up the remaining mess with a grinder and sander took only a couple of hours more than that.

  Fresh start for differential clearance
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Now we're back to go status. We only need to cut a new tube and tack it into place so we can try fitting the axle again. And then we have to figure out a way to widen the transmission tunnel at the rear without taking away too much space from the driver. And then we'll have to hope we still have enough clearance on the right side of the differential housing, although we already have a contingency plan for that, which involves lightening the axle in strategic locations with the angle grinder, and who wouldn't think lightening a heavy MGB rear axle wouldn't be a good idea?

Locost frame relaxing in the grass  
click to enlarge

If this is the last frame tube we ever have to cut out and move, I think we'll be ahead of the game. Of course no Locost space frame chassis will ever be perfect, and we're not about to buck that trend, so while we could trial fit the engine and transmission in the frame now, that's a lot more work, and so I think we'll hold off on that until we have the suspension on the car. In any case, we installed the engine and trans in the mock-up frame several times and had lots of clearance, so we're pretty sure they'll fit easily. In fact, until yesterday we were positive.


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