a common, semi high torque motor often overlooked... a windshild wiper motor.

but, day late, and dollar short, looks like the problem was solved.

 

a common, semi high torque motor often overlooked... a windshield wiper motor.

but, day late, and dollar short, looks like the problem was solved.

been thinking to install a windshield wiper motor, so is there any easy way to do this? can anyone give some helpful guide?

thanks.

 

slamdvw, I agree about the great potential utility of windshield wiper motors and window winder motors. In fact, I was searching the All Electronics website for the listing of the automotive worm gearhead motors that I had picked up some time ago, "just in case," when I stumbled across the DCM-315 that I recommended above. However, I believe that the DCM-315 would be much more suitable than a randomly selected windshield wiper motor for a welding rotator primarily because of the fairly high basic no-load speed of typical WW motors.

I was looking at two new automotive WW or window motors from All Electronics in my motor drawer . Judging from the torn plastic bag with the ALL label, the two were sent under the same catalog number, DCM-61 (but I could be wrong that they both came under that number). The best and most suitable one runs at 32 RPM at low current (0.9 amp) at 12 volts, no load, and is extremely quiet and smooth. No mfgr. or part number printed on that one. This one could probably be throttled down to a useable speed for small workpieces on a directly mounted turntable.

The second draws 9 amps at 12 volts, no load, is fairly noisy, and runs at 160 RPM. This one is clearly not suitable for a directly driven work rotator due to speed. It gets very flaky if you reduce the voltage enough to get down to even a few RPM, which is still too fast. Lots of cogging, low torque, and stalls easily requiring higher voltage to get it started again.

Each of the automotive motors were about $15 to $17 a year ago (don't remember exactly), but I think the DCM-315 for $79 would be far more suitable for a direct drive turntable for workpieces up to, maybe, 100 pounds. Of course, the automotive motors would be fine if provided with further speed reduction, but then you are getting into a more complex project, having to provide a pulley and belt or gear arrangement and bearings to support the turntable.

I realize this is too late to be of any help to Jeff, but maybe some others out there are interested in building a cheap rotator.

awright

 

awright gave me another idea. How about a nice big surplus stepper. Direct drive. A PIC and a stepper driver would make a perfect controller.

 

I have not built a home brewed rotary welding table, but have worked with many different versions. Really it should not be a difficult project for many of the clever people on this forum. I encourage people to go for it!

One of the stumbling points to making a welding positioner is how to make the rotating electrical ground connection. Generally you have a stationary ground cable connected to a "brush" of some type, that rubs on the surface of the rotating shaft (or a bushing on the shaft). The most expensive rotating ground I've used was a precision mercury filled unit that cost $5000 (what a waste), and worked no differently from a simple home made braided copper strap wrapped around the shaft.

If you are going to make your own positioner, don't sweat the rotary ground, try the braided copper strap.

Or, simply attach the ground cable to the table, pre-wind the cable opposite of your welding direction, and let it unwind as you weld. This will work fine, unless you need to make a whole bunch of revolutions in one continuous weld.

Keep it simple, Stupid.

 

I would really think that any sort of rotating table, even manual powered, would be helpful. I am just thinking about how many times I have had to weld around a pipe or something and had to take more time than the weld itself took just to reposition the part in the vice, or try to prop it up at another angle. Being able to keep the part secure, or even relatively secured, and then move the whole table to make your way around the part (even if it isnt in one continuous weld), would still help. And without all the hassle and worry of making it motorized, this could easily be an afternoon project.

 

phila.renewal, while a stepper might be suitable for a welding rotator if driven by a microstepping driver, such a driver is somewhat expensive and surely not easily implemented in a simple PIC project. Used with a simple phase-switching, full-step driver, virtually all step motors will have a 1.8 degree or larger basic step size which would be too coarse for any but the smallest workpiece. For example, the tangential step distance for a 3" diameter workpiece on a table driven directly by a common 1.8 degree (200 steps/revolution) motor would be 1/20 inch.

This coarseness of motion could be reduced to any desired degree by providing an additional speed reduction stage using gears or belts, but then you loose the simplicity implied in the direct drive you suggest.

Another limiting factor in using a direct drive stepper is that, in the absence of a physically or electronically implemented viscous damper, for some polar moment of inertia that could easily be reached with a welding workpiece on a turntable, a stepper will either refuse to step and will just shudder or will step erratically in response to a step command. This could really mess up a weld bead.

Microstepping drivers allow steppers with modest resolution, like the 200 steps/revolution that is most common, to be driven at much smaller steps limited only by the sophistication of the electronic driver but, once again, you lose the simplicity and low cost implied in the directly driven stepper concept.

All in all, I do not think a salvaged stepper motor can compete with the simple DC motor and high ratio gearhead as a welding rotator in the absence of a further speed reduction stage or a microstepping driver.

awright

 

Oh yeah. I forgot to mention that All Electronics that I linked to in an earlier post has a neat little package consisting of a 1.8 degree stepper motor coupled to an 18:1 triple spur gear reduction box. For someone wanting a light duty rotator for fairly small loads using a stepper motor, this could be a nice starting point. No way of knowing an actual load rating, but just looking at the one I picked up several months ago, "just in case...," I wouldn't be surprised if it could handle 20 pounds or so if the load was not cantelevered out too far from the gearbox.

The downside is that the 3/8" shaft emerges from the gearbox on the same side that the motor is mounted on making mounting of a turntable slightly more difficult but still definitely feasible. There is also an electric brake that should be removed.

Check it out at:

http://www.allelectronics.com/cgi-bin/item/SMT-94/search/STEPPER_MOTOR_WITH_GEARHEAD_.html

$15.35.

They also offer a sophisticated modular stepper motor driver:

http://www.allelectronics.com/cgi-bin/item/RD-022N/400/STEPPER_MOTOR_DRIVER_.html

$45.00

but note that it is rated at only 1.5 amps per phase while the motor on the gearbox is rated at 2.2 amps per phase. I do not know enough about these things to give accurate advice, but I think it would be possible to trick the driver into working with the motor at reduced torque by adjusting the current limit or padding the motor windings up with low value power resistors. With the 18:1 gearbox, I don't think the loss of torque would be any problem at all.

Assuming they would play together nicely, and I think they would, you'd have a neat starter package for a light duty rotator for about $60. You would have to provide the power supply (they might even offer a suitable one), a turntable, supporting brackets, and a simple variable pulse rate generator.

awright

 

For manual use what about using an old large bearing? We have some removed from pumps that are about 6the or 8" diameter. I don't know if it would hurt the bearing if you ground to the table but might be worth a try

 

You might like to have a look at the positioner I built a while back. The thread includes the woes of looking for a suitable motor.

http://weldingweb.com/showthread.php?t=38381&highlight=positioner

 

Mmmm just seen the date of the first post

 

Shox Dr, since you've opened up the topic again, I'll add a comment.

First, very nice job! I like the grounding strap scheme. However - - -

I wonder if you've insulated the motor from ground or insulated the turntable shaft from the motor. If not, welding current will divide up between the motor bearings and the ground strap on the shaft according to the relative instantaneous resistances of the two paths. Initially the ground strap undoubtedly has lower resistance to ground than the motor assembly, but with a little dirt or corrosion buildup under the ground strap, the current through the bearings could eventually become significant. Any resulting bearing damage would build up slowly (unless you had a serious, albeit unlikely, failure of the ground strap in which case the damage would immediate) and you might not know it was occurring until serious bearing erosion had occurred over a long period.

I would either insulate the turntable from the motor or float the motor from ground and rely on the ground strap as the safety ground path for any motor fault current. The latter approach undoubtedly violates electrical codes, so research it yourself and use your own judgement. I am not an electrician.

I speak (well, actually write) from the experience of having the bearings of the motor of an expensive front-loading washing machine fail after less than a year of service. Disassembly revealed absolute proof of bearing erosion due to electrical discharge through the bearings to ground. The sources in this case were the current spikes through the bearings due to the very fast rise times of the square waves driving the switched-reluctance motor windings from the solid-state motor controller. The fast rise time driving pulses were coupled from the windings to the rotor and thence to ground via the bearings. The bearings looked like they had been running in sand.

The manufacturer would not acknowledge the engineering problem but offered to send a repairman out to replace the motor at nearly the price of a new machine or to sell me a replacement motor for only 1/2 the price of a new machine. I opted to buy new bearings for $20 from the local bearing supply house and (after some experimentation involving viewing the current spikes to ground via the motor on an oscilloscope) to lift the ground strap from motor to dryer chassis and use insulated bushings under the motor mounting bolts. I did make damn sure the dryer chassis was well grounded and hung a large tag on the motor and stuck a label on the back of the machine warning any future repairman that the motor frame was ungrounded. The dryer has worked flawlessly for about 15 years since then.

The safest alternative on your turntable would be to keep the motor grounded and provide an insulated bushing between the grounded turntable shaft and the motor. It looks like a direct, metal-to-metal connection in the photos.

awright

 

Check this out...
http://www.ebay.com/itm/130594241759?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

this plus a slow speed motor to get the IPM you need..