Earlier, wright1902glider wrote:

Just wondering what the general consensus is on the best method of
welding 4130 tube structures. Advantages / disadvantages of each
considering I will be building in an attached garage, in a residential
subdivision, and will be limited to a 110AC/ 20 amp service?

Is an off-the-shelf MIG unit like a small Lincoln or Hobart worth the
money? Anyone have any experience with these machines?
...

I've got a little Hobart 125 MIG welder, and it's fabulous for zapping
together tooling, jigs, and fixtures out of cheap mild steel tubing.
Used with .030" flux core wire, it's the bees knees for making quick
and slaggy but perfectly adequate welds. I don't know what I'd do
without that machine.

Used with .024" solid core wire and shielding gas, it can make fairly
pretty looking welds on thin stock, including typical aircraft sizes of
4130 sheet and tubing. However, it takes a better touch than I have yet
developed to get welds that I'd consider to be of aircraft quality.
With the power and feed set low enough to get good control the
penetration isn't there; and when you raise the power and feed to
penetrate it's wicked hard to hold precise control.

Some day I hope to get a TIG rig for doing the fine stuff stuff, but
until then I do it with OA. What I do sometimes is tack stuff in the
jig with the Hobart, and then do the final weld with the nice little
Meco Midget I got from Tin Man Tech -- it's perfectly sized for thin
steel.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24