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Welding turntable grounding contacts

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  • Welding turntable grounding contacts

    I want to put together a welding turntable, and I was looking at options for the grounding contacts. I saw this picture where it looks like the brushes are riding on the steel shaft.



    That would make things a bit easier, but I wonder how well it would work.

    What sort of surface finish and contact pressure would be needed?

    I was thinking of using brushes from a Chevy starter motor, like these:

    Any products mentioned in my posts have been endorsed by their manufacturer.

  • #2
    Why not- while you're at it, why not pick up a piece of copper pipe large enough to slip over the stem. You can notch into the ends to allow you to fold fingers in to touch the stem, then put a clamp around the fingers at each end of the copper pipe. This will give you about a dozen or so tight connections from the copper pipe to the rotating stem, for a low resistance connection. The brushes can ride on the copper pipe. The copper pipe will dissipate any heat from the brushes very quickly, and if you seat the brushes to the curve of the pipe you'll have a pretty good contact. The brushes are made to ride on copper after all- just make sure you clean it well to start with, and keep it clean. I would think that you should provide some individual spring pressure to each brush to maintain each one in good contact. I don't think you'd really need more pressure than what you'd find in a starter motor spring.

    I haven't learned to weld (yet) but I suspect that you would want a reliable and consistent ground connection on something like that. I would not run the brushes directly on the steel, no matter how smooth you make it.
    Last edited by darryl; 12-12-2011, 03:17 AM.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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    • #3
      I don't quite understand what the fuss is about. I have a simple steel collar with a tab welded on it on my rotary spindle. It seems to work fine for the work I do (140 amp max DC stick welding).

      I don't see a spring to keep the brushes in good contact with the shaft on the unit shown? I would suspect that relatively light springs would be all that would be required - just enough to overcome the resistance to bending of the wire braid and to maintain contact. It may be adviseable to shape the brushes to the shaft to prevent arcing between the flat surface and the shaft?
      Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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      • #4
        I made a grounding ring that bolted to the back of the chuck and a spring loaded lever to contact it. Clamp the ground onto the tang of the lever and go welding...
        That way none of the current goes thru the headstock bearings...or so I'm told.
        Russ
        Last edited by torker; 12-12-2011, 06:19 AM.
        I have tools I don't even know I own...

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        • #5
          Mine is a chunk of 1" Bronze round bar I had laying around spring loaded inside a insulator.The contact end is turned down to a point with a 3/8" diameter contact area.It makes contact on the back of the chuck backing plate.It's been working pretty good for a couple years now with little wear on the contact.

          Mine started out with the same Chevy brushes which worked pretty good,but the new system works better since I don't have to change brushes every 20-30 hours.
          I just need one more tool,just one!

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          • #6
            We're repairing this welding turntable for a customer right now, it uses a spring loaded pad that sandwiches a piece of 1" thick graphite between the table and base.

            base with two spring loaded pads


            The table

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            • #7
              Just get yourself a braided ground cable. bolt your ground cable to one end of the ground cable from the welder. (yes I know it is not really a ground cable) and onto the table somehow. Then just wrap the braided ground cable a half wrap around the turntable shaft and attach a spring to keep contact to the shaft.
              Location: The Black Forest in Germany

              How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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              • #8
                Here is an excellent approach to welding positioner grounding that Black Forest is trying to explain (see post#8): http://www.practicalmachinist.com/vb...otator-231798/
                Mike
                WI/IL border, USA

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                • #9
                  Camdigger if you look very carefully you will notice that there are 2 springs for each contact look for the rivets.

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                  • #10
                    The one I saw that was a commercially built unit that somone removed from a machine and used it for a manual set up. It haad 4 sets of spring loaded bruse type contacts and the were submersed in oil. My guess is it was some kind of cunductive oil that help eliminate arcing and lubricated the brushes at the same time. It also had a limit rating for amperage, but I can't remember what it was. The more current you pull through it the more the resistance becomes and the shaft becomes harder to turn. As someone else pointed out you don't want to pull a currant through any ball bearing as they will arc out quickly.

                    JL................

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                    • #11
                      Here's what I did:

                      http://bbs.homeshopmachinist.net/showthread.php?t=46599
                      Who do I think you are...?

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                      • #12


                        Now, that's disgustingly simple.

                        Any idea how long the braided cable will last?
                        Any products mentioned in my posts have been endorsed by their manufacturer.

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                        • #13
                          It should last for a very long time with the low RPM and infrequent HSM use.
                          Mike
                          WI/IL border, USA

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                          • #14
                            We had several of them in my shop in USA. After we built them I don't remember ever having to change the braided cable. We used them a lot in a commercial fab shop.
                            Location: The Black Forest in Germany

                            How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                            • #15
                              What way do you spin em? On that one, I can see clockwise as causing extra friction as it tightens up. Counterclockwise would cause the spring to loosen slightly, automagicly freeing it up to a reasonable friction, but maybe causing more arcing/stick-slip.
                              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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