Making a whatsit

    --For a long time I've wanted to have a rotary welding table so's I don't have to weld round stuff in 4 sections, turning the assembly each
time. Well they're available but they cost a bloody fortune. So my idea was to modify one of those windshield wiper motor assemblies, the ones with the 20-to-1 worm drive. Turns out that's not nearly slow enough, even with the finest motor controller. I'd messed around with the idea of adding a gearbox to slow it down further but the cost of the components wasn't small. Then a pal suggested I couple two of the worm drive units in series and that's what I've started to do. Here's a photo of the 'output' stage; so far I've removed the motor and machined a shaft support. Support has an internal oilite bushing and shaft has a collar inside to limit longitudinal play. More photos to follow when I get more built.. http://www.flickr.com/photos/steamboat_ed/5951397160/in/set-72157624880649814
--
"Steamboat Ed" Haas : Steel, Stainless, Titanium:
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On 7/18/2011 10:43 AM, steamer wrote:

I built one several years ago using a commercial Christmas tree rotator. Had a fair sized variable speed AC motor with a husky gear reduction box. After it was built, I realized the welding current would be going through the gear box to get to the table. I thought about just clamping to the table, but that would mean it would be dragging the cable around in a circle.
I gave up and tore it up, and donated it motor/gear box to a handicapped metal worker to raise and loser his drill press table.
How do you intend to clamp the welding cable, or are you only using gas?
Paul
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You should probably use some heavy duty motor brushes and a slip ring. Our big DC motors at work have 3 or 4 brushes in parallel to handle the motor current. Might be able to salvage motor brushes and holders from a scrapped DC motor. I suppose a person could make a pretty good slip ring out of a couple of inches of copper bar or pipe.
RogerN
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    --Plan on doing TIG and MIG with it; the design isolates motor assembly from table assembly with a Lovejoy coupling. Motor is isolated from all welding equipment this way and rotative part is sitting on steel welding table. First try I'll clamp ground to table and see if the table can connect that way. If contact looks spotty plan B is to attach a cable to underside of top plate, long enough to allow one 360 degree rotation.
--
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Hi Ed. I have built 2 so far. One was an amazing conglomeration of Boeing surplus pieces. It can act as a turntable or a lathe.
The optimal RPM range is 0 - 10.
The second one I built was a conversion of a turntable unit that was originally set up as an automated deburing station. That one is awesome because it has a pneumatic 3 jaw chuck in the turntable. It is strictly a turntable, but I prefer it for flange welds. I ground the first one by simply clipping my ground clamp on the other end of the shaft the lathe chuck is mounted on. I pinned a bronze bushing on the shaft for the clamp to spin on.
The second one was more complicated. I installed a ring of copper flat bar around the perimeter of the air chuck and rigged a pair of huge motor brushes to spring against the ring. I ran heavy copper wires into the chuck to connect to each of the 3 toggle arms, and used bronze bolts for the grippers on the arms.
I have an idea for a really simple turntable positioner using a lazy susan bearing. If you took a large lazy susan bearing in the 8 - 10 inch range. Place a round steel platter on top for a welding surface. Install a spring in the middle of the underside of the platter so it simply grounds to whatever table it is sitting on. Now all you have to do is drive the platter from it's edge using a small variable speed motor with a roller wheel on it.
The entire unit would be maybe 2 inches tall and 12 inches in diameter with the motor mounted on one edge.
It would solve one major problem I have with both of my positioners which is parking them somewhere when not in use.
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    --Hey Ernie got any photos? I'm having some problems visualizing.. :-)
--
"Steamboat Ed" Haas : Steel, Stainless, Titanium:
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Pictures of my existing ones or the idea I have for a simpler one?
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    --Either would do. Meanwhile here are a few more photos of my contraption: http://www.flickr.com/photos/steamboat_ed/5959456475/in/set-72157624880649814     --Stuff left to do: hook up a little PWM controller I built from a kit and modify it to vary speed of table with a foot pedal.
--
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    --Have found a decent controller that costs abour $20.- and seems to run the table smoothly down to about 1/2rpm. Max speed is about 5 which is adequate for my skills.. ;-)

    --Now this is pretty kewl; you mean you clamp to the bronze bushing for grounding?

    --This is sort of where I think I'm headed. I found some really neat EDM electrode barstock in the warehouse and I've cut a piece to act as a "brush". I'm going to make a pedestal mount for it with a spring beneath it pushing up. Thot I'd mount the pedestal to the baseplate with 2-sided sticky tape to insulate it from the rest of the mechanism so that the current path will be biased from torch to work to table to brush to pedestal to ground clamp.
--
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    --Well as of this evening the thing is done but I foresee a weak link in the form of the spring that's pushing the 'brush' against the now copper plated bottom of the rotary table. That spring's mighty skinny and I'm thinking it might just blow like a fuse. So now I'm looking for a weak spring with a good cross section. Any ideas? It needs to fit in a 1/2" bore..
--
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On 7/24/2011 7:02 PM, steamer wrote:

You're at the point where I gave up and disassembled the whole thing. Better luck to you. Paul
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    --Aha! Had an idea! Will try making a 'spring' with a stack of Belville washers. Whaddya think?
--
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    --Had another idea that would provide a bit of push on the graphite without using a spring at all: put it on a fulcrum, the other end being pushed down from the weight of the grounding clamp. Vertical orientation can be maintained using Watt's parallel motion. It's just silly enough to suit my 'steam nut' sensibilities too.. ;-)
--
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steamer wrote:

How about leaving the spring in place and adding a bit of welding or braided cable between the brush and base to take the current, the cable being much lower resistance the spring should be fine.
I recently made a small hand rotation jig to weld some pipe couplers into pieces of plate, the pipe coupler was mounted on a brass boss and held in place with a washer and bolt and the bolt had a crank handle welded to the top to allow it to be rotated. The brass boss was drilled just over 3/4" about 1.5" deep and ran on a 3/4" copper bar I had and that had the ground cable attached to it. I was running MIG at about 130A and this set-up allowed me to rest the torch in one position and rotate the part producing a nice even quick weld. NO sign of any arcing or whatever on the surface of the brass or the copper so wherever it was making contact the conduction was good.
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    --Hmmm that sounds like a plan; didn't read this 'til after I ordered the washers tho so your plan will be "B", so to speak. Here's a link to the washers I ordered: http://www.mcmaster.com/?orderview=new#9712k61/0eqx
--
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    --Followup to followup: replaced spring with Belville washers but they turned out to be way too stiff to function as a decent spring for this application. Next thing I did was lash up a Watt parallel motion linkage and I'm happy to say that works a treat! Took it to Dorkbot last night and the gang suggested I use your idea of attaching grounding clamp via braided cable and that's the next bit I'll be doing. Will try to post photos tomorrow.
--
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    --Created a seperate set for the project and added photos of the parallel motion setup at the end: http://www.flickr.com/photos/steamboat_ed/sets/72157627324267926/with/5994453177 /
--
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steamer wrote:

http://www.flickr.com/photos/steamboat_ed/sets/72157627324267926/with/5994453177 /
Very Nice, Ed!
I am interested in the Testing Phase as well.
--Winston
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http://www.flickr.com/photos/steamboat_ed/sets/72157627324267926/with/5994453177 /
Looks good Ed.
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    --Thanks! Today I started on the foot pedal speed control: http://www.flickr.com/photos/steamboat_ed/6000572305/in/set-72157627324267926 Will try to get it finished tomorrow...
--
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