One of the features of our new low cost  universal motor mount I am
working on is there are four tubes that need ball joint adapters tig welded
to the ends. Eight joints per motor mount. This is easy to do for a skilled
tig welder but it is like riding a unicycle while juggling for me. I can
get a functional joint but it is far from cosmetic. I have to stop...weld
about 30 degrees.... stop.... rotate the tube 30 degrees and do another 30
degrees.

There must be another way so I am building a robo welder just for this
job. I'll offer it as a service because it only takes a few minutes for
each joint.

Pololu $22 gear motor has a 1000:1 gear reduction so it is slowly rotating
the the tube at a constant rate. You just need to come up with the correct
distance for the tungsten and the right welding current and gas flow. The
rest is automatic with my Lincoln 175 tig I bought at Sun N Fun on sale.


The rollers that turns the tube are plastic as you don't won't 80 amps
flowing through the gear motor. There would be a spectacular fire with a
pool of liquid metal :)


The copper colored parts are just that and they necessarily ground the
4130 tube. Copper does not weld to steel.

Paul Lamar

Paul,  I built one of these years ago to do boring welding at
our shop like putting hubs on gears or the end of a tank.  I
don't think you want to have your ground dragging on the part as
it will leave arc pits as it conducts.  I put a pointed vertical
shaft (1-7/16") into a grounded carbon block.  Mounted the shaft
in two brass bushing sleeves under a 4' square table.  There was
a 20" circular work table the part set on with some adjustable
centering blocks like a lathe chuck.  I turned the shaft with a
variable speed 3/8" drill with the trigger locked on and running
thru a rheostat from a wire feeder as used on our MIG welders.


The drill turned a 100:1 gearbox and had roller chain drive to
the vertical shaft with about a 4:1?  sprocket ratio.  I have a
cover that closed everything inside for smoke control with a
large welding lens in the cover and a hand hold hole to set and
adjust the tig or mig gun while it runs for irregular shaped
parts.  It welds 1" to 20" diameters with the same drive
sprocket and could do much larger with more sprocket reduction.

This rig welded thousands of parts with only the drill motor
brushes being replaced a couple of times.  I also built one like
your sketch to weld headers shafts, and caps on roll case
rollers.  There was a sleeve that slipped over the end of the
shaft for the ground clamp and it just twisted the ground cable
360 degrees to weld the part.That machine was used but not as
trouble free as the vertical one.

The big problem was the work
walking along the support rollers end wise.  That was patched by
tilting the rig a few degrees and having an adjustable end stop
on the opposite end of the welding.  The plastic rollers
(UHMW-green) didn't drive worth a crap.  Real irregular feed and
stop and start while welding.  I changed to steel wheels and put
a third weighted wheel on top at the drive set.  It then worked
well but seemed like more trouble than it was worth.

We
continued using it but should have built something else.  If
you like the vertical spindle you could have a threaded stub
sticking up to screw your weld bushing on and slide the tube on
till the shoulder of the sleeve.  One other thing, I had a limit
switch to stop the rotation at exactly one revolution.  The
start button bypassed the NC limit switch and started the welder
thru a 3 pole glass relay.  The limit switch unlatches the relay
to stop.  An idec solid state timer left the welder run a second
or so while the motor coasted to a stop to overlap the end of
the weld over the start point.  These things did a wonderful job
with shield gas and flux core MIG welder but it is really hard
to get tig set up.  A SS guide sleeve for the filler will aim it
but an operator must work the wire in and out to apply it.  A
really tedious job.

george grimes

Thanks for the tips George. I'll let you know how it goes.

Paul Lamar