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Thread: Rotary welding table earth
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14th July 2015, 06:42 PM #1SENIOR MEMBER
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Rotary welding table earth
G/day fella's, I am about to build a small rotary welding table and was hoping for some info on rotary earth clamps.
Has anyone used one of these ? http://www.sumner.com/sumner/sub/pro...11.91.0.0.html
If so what material is the pivot pins made out of ?
By enlarging the picture it appears to have bronze bushes ?
Do those earth clamps work ok ?
Does anyone have a better idea for a rotary earth ?
cheers, shed
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14th July 2015, 07:04 PM #2GOLD MEMBER
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Hi Shed,
When I had my business, the bloke next door welded extension handles onto ratchet handles for Manutec, all he used was a welding clamp that had brass blocks where they gripped the handle. Handles were chromed and shiny, don't know if it made a difference. He used a 3 jaw chuck hooked up to a VS motor, and a timer on the welder.
Set the motor going, set the MIG going, after it timed out weld was finished, switch off motor. Job done.
Kryn
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14th July 2015, 07:51 PM #3Philomath in training
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Depends on what you need to weld and how fast. The welders I've worked with typically have a rotary table that is as simple as a piece of pipe rotating on a pin. The earth is just a stripped back piece of earth lead that does a turn or two around the pipe so it is always in contact (perhaps with a spring or weight to help)
Michael
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14th July 2015, 09:15 PM #4SENIOR MEMBER
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Have a look at this guy's build. He talks about his earthing arrangement in this video.
https://www.youtube.com/watch?v=LsUq2I4TiFo
Cheers
- Mick
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15th July 2015, 09:12 AM #5SENIOR MEMBER
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Thanks for your reply's Kryn, Michael and Mick.
I am concerned about damage to the shaft from arcing ? This the unknown to me, so I think to prevent damage to the shaft
I will make a replaceable slip ring and ad a copper brush as in the youtube that Mick pointed me to.
Has anyone an idea what is the best material for the slip ring ?
Would copper to copper be better, or maybe copper to brass ?
Has anyone seen what is used for this in a professionally built machine and seen what sort of wear/damage I could expect
from erosion caused by the arcing ?
I think getting the earth right will be the key for all around successful automatic mig welding.
shed
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15th July 2015, 02:58 PM #6
Years and years ago I operated a large rotary table, it took a 5 ton load for sub arc welding the inside of 600mm Lunkenheimer valves. The sub arc machine could punch out up to 1200 amps:yes that's 1200, no typo.
The earthing was achieved by a couple of was brass discs say 100mm x 12 mm diameter, 1 fixed to the rotater and 1 that pivoted on a bolt that run through the and was fixed first plate.
The pivot plate had a compression spring tightened by a nut and washer forcing it to the face of the rotating plate and was tapped for an earth bolt for the earth return lead. This all mounted directly on the end the rotating axle.
For smaller application perhaps you can use some smaller diameter brass bar with the appropriately faced contact faces. Whether the brass was special stuff or not I have no idea.
Edit > With further thought on it, make sure the motor earthing is quite separate . A welding circuit with a failed earth, basically can find the easiest way home, so to speak.
This can be through your motor wiring. There's quite a lot info on Google ,but when it is all said and done, there's nothing like a check over from an electrical professional, particular one versed in welding electrics to give peace of mind.
I can recall a work colleague who forgot the gantry crane was hooked to to the job and there was a bad earth back to the welder. He cooked the crane motor and wiring as the earth sought and found a different path.
Grahame
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15th July 2015, 06:26 PM #7SENIOR MEMBER
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ha...1200 amps, a lot of grunt there Grahame, how close you were standing to that ?
I worked at Coonara heaters for about 6 wks 25 - 30 yrs ago, in summer, welding the 4 corners of the hot boxes, from memory
360 - 380 amps with 1.2 wire.
I was sure I had died and gone to Hades, the factory was hot, the boxes were hot when they got to me and pulling those vertical downs was hot hot hot......
Anyway back to the subject, a big grunty carbon brush or 2 with a big grunty wire/s attached to it/them and brass slip ring ?
Overkill ???
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15th July 2015, 09:03 PM #8
The sub arc welds were internal and most of the heat was radiated from the hot valve body.The wire was 4 or 5mm .All I had to do was let it rotate one turn and the advance the sub arc head positioner for weld overlap and rake out the flux for recycling. The beads were 25mm across and flux was shot enough to blister skin.
Good job in winter night shift, but awful in summer day shift.
Can't say about carbon brushes ,but have seen a smaller rig to what I described, with a slip ring and flat copper woven straps ( like the old time battery leads) that were under some form of tension - never had a real close look look at it though.
here are some pics if its a help.
1. Similar to old battery strap works against steel shaft ok note spring
2. Pipe earth clamp like you have shown - probably not suitable unless you have a pipe like spindle.
3. Spring loaded disc against disc spring loaded - works on axis of spindle
Grahame
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17th July 2015, 04:42 PM #9SENIOR MEMBER
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Thanks for your input guy's
I think I'll go the braided cable path as it seems to be used on a few of these machines without problems, cheap and easy to implement and if I am not happy with it and I stumble across a large carbon brush then I can always change it.
shed
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