On Thu, 26 Mar 2009 10:59:08 -0700, "Stuart Fields"
wrote:


wrote in message
.. .
On Wed, 25 Mar 2009 16:41:35 -0700, "Stuart Fields"
wrote:


wrote in message
...
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

Harry: Thanks. Because of your post I bought a copy of Finch's
"Performance Welding". The fault I can find, is that I was too stupid to
buy it earlier. It can be used as a handy reference by this amateur
welder.

thanks
Stu Fields

Just remember that although the book is good, he's not ALWAYS right.
Some pro welders I know have had a few bones to pick with his methods
and theories on a couple points.
His work, usually, but there are apparently better ways to do some
things based on current technology and knowlege in the welding field.

Cla Have you got any references to the improvements over Finch's work?
I recall some interesting things that I found in the TIG welded (certified
welder) 4130 tube crashed helicopter,(mine). Some of the breaks in the
tubing were what looked almost like a pipe cutter had made a clean cut just
a short ways from the welded joint. The breaks looked like a brittle
failure. There was little if any distortion to the tube. Very stress
concentrationy type of a break. With all that said, I've trailered my
helicopter more than 120,000 miles in support of our magazine, attending
fly-ins all over the western half of the US. Never have I encountered any
cracks or failures in the frame. This includes roads so rough that they
bounced my tail gate completely out of the trailer. Roads so rough, they
set the ELT going. I estimated some 15 minutes of air time with the ship on
the trailer during one trip to Canada.
Stu

There was something about not using copper coated rod on Chrome Moly
tubes. Professional welders I know say it is a non issue and better
than using oxidized rods.

Post heating od a tigged joint, if cooled in still air is not
required, and some say is better not done.

What rod is he recommending for chrome-moly tig welding? IIRC he is
saying to use chrome moly rod. The proper is a mild steel rod - it
draws the alloy from the joint and the joint being thicker has the
same strength as the tube - and you don't get cracking just back from
the joint because the HAZ is softer, not harder.

Something like that anyway.