Thanks everyone, especially Bob, for the tips and encouraging words.

I spent a few hours working with the tubing notcher on Fri. night and
Sat. morning. Between it and a little clean-up with the *******, I'm
getting fit-ups that look as tight as the ones shown in Finch's
"Performance Welding" book. I'm very comfortable with that process.
The only tricky item left is to get tubes that are the correct length
when notched on both ends. Shouldn't be too hard, that's just a matter
of working with the tool and making a few reference marks and maybe a
wire-pointer on the clamp of the thingy.

I practiced with the torch Sat. afternoon for about 2 hours, mostly
making 90-degree joints. They still look pretty awful and lumpy, but I
did learn what a burn-through looks like just before it blows out into
a giant hole. I think most of my tubes were cut too short though. On
the order of 2" or less. The longer tubes had better beads. I know,
heat concentration and accumulation in the short tube. Got it. I've
also learned to aim the flame at the uncut tube until it's nearly
molten and then drop the flame onto the edge of the cut tube so the
two will start to puddle at nearly the same time. Not easy. Works on
the flats though, which is where I was making my tacks. I'll keep in
mind the shrink-fit factor next weekend and watch for it when I tack.

Another method that I tried was starting in the crotch of the joints
and working out toward the flats. I would heat both tubes up to
yellow, and then aim for a few seconds more on a single tube. Just as
a pool formed, I'd put a drop of filler in it, then aim at the same
spot on the opposite tube and repeat, then back to center, which
caused the two drops of filler to spring together like two water
droplets! Now that they were joined and both molten, I aimed the torch
back to center and it was drip-drip-drip-drip right up the side and
out onto the flats! Well... it worked like that for one or two beads
anyway. Just enough to be encouraging.

I'm still having trouble controlling the heat and the timing of the
filler, but I was better this weekend than last. I'll keep working at
it. I may have to work on getting the tubes cleaner too. There seemed
to be a lot of micro-boiling this weekend. Maybe that also has
something to do with my inability to manage the heat correctly? The
micro-boiling was happening well in advance of the puddle and left
sugary-looking spots on several of the joints. I'll save that problem
until I can at least run a bead though.

Harry