Smooth Lady - Getting It Together
To jig this up for tack welding, I just set up firebrick on the garage floor (the best flat, non-flammable surface I had available) and pinned the tailpipe in place with two more slabs of firebrick. The front corners of these slabs extended beyond the front edge of the tailpipe just enough to align the rear of the chamber cone with it. Side-to-side alignment of the chamber is essentially automatic, due to the good fit of the intake pipe to the front end of the oval slot in the top of the chamber. You may have to gently bend the intake up or down slightly at the 'spade' to get a near-perfect fit. Near the rear, I had to push the cone edges down in a bit to lessen the gap - note the fairly wide gaps between the chamber cone and the edges of the 'spade'! (I really should have cut the 'spade' area closer to a full inch wide (25mm) to achieve a better fit.) For me, such gaps are no problem, but they can be rigorous (but excellent!) practice for beginners.
You need plenty of tack welds to lock things together. Note that the EMT intake pipe is a little thicker than the chamber cone shell, so you need to concentrate your heat more on the intake tube, less on the cone edge. Here's a shot of the tack welded assembly after cooling. The gaps between the 'spade' and the cone edge can clearly be seen here, near the right edge of this photo. Note that there are tack welds around the seam between the cone and tailpipe also (you can just barely see them in the photo) - for these, you have to pick up the assembly out of the makeshift jig and turn it over.
Once the tack welding is in place, you're ready to finish weld the cone to the intake and tailpipe. Start with those two gaps - use a small flame and all the patience you can muster, and bridge them in, working gradually forward from the rear. Be extra careful to bridge right up to the point where the previously done welds along the sides of the spade ended (just a few mm forward of the end of the intake tube). Next, turn the assembly over, and again with a small flame, work around the seam between the tailpipe and the rear edge of the chamber cone. Just weld from tack weld to tack weld, blending them in as you go. Try to use as little filler rod as possible, so the underside of the weld will be kept fairly smooth inside the pipe. Once you've completed smooth, unbroken weld around that seam, you can do the final weld all around the top between the intake tube and the cone shell. You can use just a little larger flame and considerably more filler rod for that weld. It can be done a little at a time, from tack to tack, as long as you get continuous weld - no little gaps or holes. Again, the tube is a little thicker than the cone shell, so you need to keep the bulk of your flame on the tube, and just flow the weld puddle into the shell edge and blend it in. When you're all done, it ought to look something like this:
The main thing left to do at this point is form the intake and tailpipe flares. The tailpipe flare can be easily hammered cold with a ball peen hammer, by extending the edge of the pipe 3 or 4 mm over the edge of a workbench and hammering downward on the bottom edge. Slowly roll the pipe as you go, gradually extending the slight flare all around the edge.
For the intake flare, set up the engine firmly clamped in a vise so it overhangs the edge of the bench, with scrap wood supporting the dome at the center (i.e. under the spark plug mount):
Heat the edge of the intake tube to red heat a small zone at a time and hammer gently with the ball peen. Then heat the adjoining small area and lightly hammer again. Work very gently and gradually, until you have a well-formed flare all around the top and sides of the end of the tube. You won't need to flare the bottom edge, where the intake touches the 'spade' (now part of the finished combustion chamber). If you take this process slowly and gradually, you can form a very nice flare that will work well. As shown in the original drawing, the flare doesn't have to be overly large.
The final step will be to set up the starting air and fuel tubes. At that point, you're ready to test fire your Smooth Lady!
23 September 2005