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 will need.
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
I've been kicking around ideas for a roto-weld machine like you're thinking of implementing. 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 circuitry).
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 current.
Greetings Karl, 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 corded types. ERS
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.