An M.G. Locost Build
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April 5, 2012
Thoughts on Welding

So now that we're one-quarter of the way through the Locost build plan, more than 25% done, we actually get to start building the car. It took plenty of work just to get to this point, but now we're ready. We have everything we need. We've cut up a bunch of steel and stripped down a perfectly good running MGB. We've bought some new parts and refurbished a lot of old ones. The cows are in the barn and wood's stacked in the shed. Okay, I just made that last one up. We actually don't have any cows. Or a barn. Or wood. But we are ready. It's go time.

  Still looks pretty darn good
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The MGB chassis left the premises last week. The dismantler picked it up with a flatbed trailer and a strong winch. I made it clear on the phone to the guy that the car would not have any wheels, but he was still a little surprised to see the chassis sitting there on the floor of the garage. Undeterred, he rolled the chassis across the street on 3 Harbor Freight moving dollies, then hoisted it high enough on jacks to back the trailer under the front end. After that it was just a matter of dragging the bare chassis onto the trailer, steel-on-steel.

Neighbors no doubt silently cheering  
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All that was left for us to do was wave good-bye as the old M.G. trundled sadly down the street. I tried to remain stoic as it headed off into the sunset, but along with the car went a lot of fond memories and fun times. Okay, maybe not that many fond memories. We actually only had the car 10 weeks, it just seemed a lot longer. And all the good stuff from the car is now sitting in my garage, along with a giant wide open space where a nice Locost chassis will fit easily. So it was sad to see it go but I got over it.

  The new Locost welding station
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In preparation for the frame build, we fired up the old Miller 140, and by "old" I mean brand new but bought last year. It had been nearly two years since I last held a welding torch, and that was an oxy-acetylene rig, but I was still pretty confident. Just like riding a bike. I figured I'd spend a couple of hours practicing on scraps, and I'd quickly be back in top form. Unfortunately it turns out there are not a lot of similarities between MIG welding and riding a bike. But after two hours I did get to the point where I could make a pretty good tack weld.

Early tack welds  
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All you have to do to make a tack weld is point the electrode at the seam, pull the trigger, and count to two. That's it. You don't even have to move the torch. You would expect this to be almost foolproof, and of course you would be wrong in our case because pointing the electrode at the seam is no guarantee that the bead will actually end up there. But like a lot of coordination-type things, you keep at it, and after awhile the bead does exactly what you want it to, and you wonder why it seemed so hard in the first place.

  Early welding attempt
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We also tried fully welding a couple of typical Locost frame joints. That didn't work so well early on, but we learned a few things. First, don't try to weld over a giant tack bead. You can do it with gas or TIG because the bead melts into the puddle, and you just hold off dipping the rod until you're past the tack. Unfortunately the MIG welder is always dipping the rod, so to speak, and the giant tack bead turns into this big lump that won't melt because it's too thick. So what you want to do before you weld a tacked seam is grind down the giant tack bead. Or else don't make giant tack beads in the first place.

Another thing we learned is that you have to be able to see the joint seam before you can start welding on it. With the welding helmet at full dark, you can't see much. The seam is nothing but a ghostly shadow somewhere east of the puddle. If you can't see it at all, you'll find yourself welding from memory, and that never seems to go well. It's a different world under the welding helmet, with limited visual cues, but it does start to become more familiar after you've been there awhile.

Not an actual Locost frame  
click to enlarge

Torch speed is another trick you have to learn. It's not a constant motion. At first contact, it's almost like a tack weld. Not a lot of forward motion, but a little back and forth across the seam. Then you pick up the pace as the surrounding metal heats up and melts faster, until by the end you're moving the torch pretty quickly with almost no back and forth at all. If you do it that way you'd expect the first part of the bead to be a lot thicker, but surprisingly the bead ends up pretty uniform all the way across.

So now I feel like we're fully qualified to tack weld the frame together. That'll keep us busy for the next month or so, and the plan after that is to be such a master with the MIG torch that fully welding the seams will be a piece of cake. Luckily we're not thinking that far ahead. Once we figure out a way to get a couple of sheets of 4'x8' MDF to the house, frame construction officially begins.


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