But first, I needed a way to put it all back together again.
You can't just butt-weld the tubes back together, that's not strong enough. Nor do you want to use solid slugs, as they won't flex as much as the surrounding tubing and hence will tend to concentrate stresses at the upper and lower ends of the tubing, right at the steering head and the motor mounts.
So, I acquired a supply of 1020 DOM round steel tubing in 0.065 wall thickness, the same as the factory frame tubing.
I got several feet each of 7/8", 1", 1 1/8", and 1 1/4" tubing.
I'm cutting these on my poor-mans-chop-saw which is a 4 1/2" angle grinder mounted to a stand I bought on Amazon for $20.
The 1 1/4 tubing will be used to extend the main down tubes. The 1 1/8" tubing will be used to make slugs for these joints.
The 1" tubing will be for fixing the auxiliary backbone tubes. I wanted to come up with something nice looking for this, even though it would barely be visible, because it would please me to do so.
The 7/8" tubing will be used to make slugs for the aux tubes.
Now, the problem here is that the slug tubing doesn't quite fit into the main tubing, so I'll have to reduce the outside diameter. No problem, just walk over to the lathe...
... but I have no lathe
What I do have is a long bolt and some cone washers...
... and a drill press ...
... and an angle grinder.
What I did was, spin the tubing at the lowest speed in the drill press and then use the angle grinder with a coarse flap wheel, moving up and down the length of the tubing as it spun. In this way I was able to more-or-less evenly remove material a little at a time, until I achieved the diameter I needed.
Barbaric, I know
but it worked! I was able to reduce the outside diameter enough to get a tight slip fit on the main tubing.
On the main tubing I had to first remove the barb left by the cutting wheel of the tubing cutter. Tubing cutters are actually "pushing" their way through the material, rather than "cutting", and instead of material being removed by the teeth of a saw, it's being deflected to the sides by the tapered carbide wheel. So the ends of the tubing end up getting thicker, leaving a ridge on the inside and the outside that needs to be removed. Also used a dremel to lightly dress down the weld on the inside of the tubing, just enough to slip the slugs inside.
To join them, I'll bevel the ends to create a weld channel, and drill cross-holes in the outer tubing in order to put in some plug welds. The idea here is that the plug welds provide much of the strength of the joint.
I don't recall what size hole I ended up settling on for the plug welds, but it was sized such that once I'd welded all the way around the circumference of the hole once, the center of the hole was filled to slightly above the surface. The pieces you see here are test pieces. I did a bunch of practice welds to perfect my technique and tune my machine settings before doing the frame for real. Also cut up a bunch of these afterwards to check penetration etc. Ended up dialing up the heat just a bit from what you see here.
mystic_1
