I scored a four jaw chuck cheap at an auction yesterday. My plan is to make
it into a turner for welding AL irrigation pipe with a TIG welder. I need
variable speed and an easy way to turn off/on while welding. Note: Both
hands and one foot are already busy. (I've been using the SO for pipe
turner - trust me, this is NOT a good idea)
Any suggestions on a source for a small variable speed, very slow, rotator.
And how to control it?
Well ... the first thought is that of where is the current
flowing -- though the bearings on the spindle of the chuck? You
probably don't need the accuracy of a lathe spindle, so I would suggest
that you start with nylon sleeve bearings, and a non-conductive belt to
take the drive from whatever motor you have to the spindle. Using ball
or roller bearings with the current flowing through them will kill them
in short order.
Now -- what *I* would probably use for the motor would be a
hefty servo motor and a matching servo amplifier. Those can be set up
to run anything from 2000 RPM down to so slow you need some tape on the
motor shaft as a flag to even tell that it is moving. Obviously, you
don't need anything near the top end of the motor's speed, so you set up
a potentiometer output a command voltage for perhaps 50% above your top
desired speed down to a full stop. A second potentiometer can be used
to enable you to set that top speed. Normal command voltage range to a
servo amp is 0-10V or 0-5V (usually jumper selectable), with the highest
voltage giving you the maximum speed.
Normally, servo motors are connected to leadscrews via a timing
belt, but you don't need that kind of precision or repeatability, so a
plain V belt will be cheaper and easier to get. (The amp and the motor
you should be able to find on eBay with a bit of patience.) Avoid
servos for model aircraft, as the don't have near the torque which you
Another possibility is to use a VFD and a three phase motor to
get the slow speeds -- but you probably should add a booster fan, as the
motor's own fan won't be running fast enough to do you any good.
As for controls -- the initial thought of putting the pot and a
switch remote and mounting them on the TIG gun is probably a bad idea,
as the electrical environment will be rather nasty -- the noise from the
work will totally confuse the servo amp. So you need something else for
that. Using your SO as a voice-operated control to the servo amp is
just a slight margin better than using her to directly turn the pipe, so
I'll leave it up to you to find some other limb to control the
start/stop (at least) with -- figuring that when it is stopped, you can
change the speed setting.
at work we use a dc motor and rheostat type controller
but I have seen ac motors with gear reduction and speed used, the actual
rotation is very slow less than 1/10 rpm , we use a constant rotation , they
sell fancy units that pulse and only move a fraction of a revolution at a
time though I have not used one of these
On Fri, 21 May 2004 01:44:00 GMT, "Karl Townsend"
vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
cordless drill, with belt drive to get it down really slow if needed.
variable trigger taken out and taken to a foot operated unit via long
Run the drill from a cheap 2A battery charger.
What this will not give is constant speed under varying load, which
the servo motors will give. But it's easy to get hold of and cheap and
easy to set up and modify. *******************************************************
Sometimes in a workplace you find snot on the wall of
the toilet cubicles. You feel "What sort of twisted
child would do this?"....the internet seems full of
them. It's very sad
I've been kicking around ideas for a roto-weld machine like you're thinking
I think I'll end up using a variable speed gearhead motor for driving the
workpiece thru a pulley and belt arrangement. As DoN suggests, the weld
current should be isolated from the drive components (including the drive
I've considered the issue of the welding current path, and have concluded
that it could be some type of slip ring and brushes, or a disk similar to a
disk brake, with some type of brushes or heavy duty conductive contacts.
A short length of heavy cable clamped to the workpiece will pass the welding
I've had my foot pedal control apart for repair. It is a Miller foot
pedal. There is plenty of room for an extra switch. Use this to turn
on a cordless drill to spin the chuck. The drill switch could be
pressed in a certain amount by using a thumb screw. Cheap cordless
drills can be had for 15 bucks. They tend to run slower than the
A local shop has a device for turning things as they are welded. It
use a couple of rollers which the pipe just lays on. The local scrap
yard has some 230 volt DC 1/4 hp motors that would work. They said
they came from an elevator company. If you want I could get you one.
The shipping would be more than the motor cost.