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winchman
12-12-2011, 02:22 AM
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.

http://www.weldlogic.co.uk/Level3%20Pics/gear-and-ground.jpg

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:

http://www.classicindustries.com/images/productimg//r/rx6004.jpg

darryl
12-12-2011, 03:11 AM
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.

camdigger
12-12-2011, 03:12 AM
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?

torker
12-12-2011, 06:16 AM
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

wierdscience
12-12-2011, 08:41 AM
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.

mochinist
12-12-2011, 09:29 AM
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
http://img.photobucket.com/albums/v471/mochinist/Mobile%20Uploads/th_IMG_7591.jpg (http://img.photobucket.com/albums/v471/mochinist/Mobile%20Uploads/IMG_7591.jpg)

The table

http://img.photobucket.com/albums/v471/mochinist/Mobile%20Uploads/th_IMG_6840.jpg (http://img.photobucket.com/albums/v471/mochinist/Mobile%20Uploads/IMG_6840.jpg)

Black Forest
12-12-2011, 09:42 AM
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.

MichaelP
12-12-2011, 10:10 AM
Here is an excellent approach to welding positioner grounding that Black Forest is trying to explain (see post#8): http://www.practicalmachinist.com/vb/general/how-ground-rotating-plate-welding-rotator-231798/

duckman
12-12-2011, 10:58 AM
Camdigger if you look very carefully you will notice that there are 2 springs for each contact look for the rivets.

JoeLee
12-12-2011, 11:13 AM
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................

HAP
12-12-2011, 12:17 PM
Here's what I did:

http://bbs.homeshopmachinist.net/showthread.php?t=46599

winchman
12-12-2011, 12:47 PM
http://i721.photobucket.com/albums/ww216/bjorn_toulouse/positioner/position4b.jpg

Now, that's disgustingly simple.

Any idea how long the braided cable will last?

MichaelP
12-12-2011, 02:34 PM
It should last for a very long time with the low RPM and infrequent HSM use.

Black Forest
12-12-2011, 03:20 PM
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.

Black_Moons
12-12-2011, 04:14 PM
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.

jdunmyer
12-12-2011, 06:57 PM
Years ago, I built a "slow-speed lathe" for welding up bulldozer rollers. The shaft was 1 7/16", running in a pair of pillow block bearings. Said bearings were used, surplus, so I didn't too much care about possible damage, plus I had a bunch more on hand. This thing ran at about 1/3 RPM while welding with a MIG and .045" wire. The power was a little bitty Boston DC gearmotor and a timing belt drive.

After the bulldozer job, I used it to build up worn rollers for a large trenching machine. Can't tell you how many hours of use it got, but it's still functional. I do remember that the 'dozer roller job took about 12 hours of arc time.

FWIW:

torker
12-12-2011, 07:38 PM
My bud Willy found this old thread of mine...
BTW...I did finally get it working well. It's in storage now...sigh..
http://bbs.homeshopmachinist.net/showthread.php?t=31921

hardtail
12-13-2011, 11:06 AM
Years ago, I built a "slow-speed lathe" for welding up bulldozer rollers. The shaft was 1 7/16", running in a pair of pillow block bearings. Said bearings were used, surplus, so I didn't too much care about possible damage, plus I had a bunch more on hand. This thing ran at about 1/3 RPM while welding with a MIG and .045" wire. The power was a little bitty Boston DC gearmotor and a timing belt drive.

After the bulldozer job, I used it to build up worn rollers for a large trenching machine. Can't tell you how many hours of use it got, but it's still functional. I do remember that the 'dozer roller job took about 12 hours of arc time.

FWIW:

Would like to see this as many antique fellas use this to repair........12 hours for how many rollers?

jdunmyer
12-13-2011, 04:39 PM
Hardtail,
There were 10 rollers and 2 idlers (those are on the top run of the track) on my J-D 1010 'dozer. It required 2 layers, IIRC, with each layer being 3 or 4 passes wide.

I have an old milling vise that I replaced the movable jaw with a piece of 2 X 2 X 1/4" angle iron. Clamped the MIG 'stinger' to the angle iron and set the entire rig on a metal table. The screw of the vise was parallel to the "lathe's" shaft and had a 3" pulley of some sort on the end. After one revolution, I'd grab the pulley and give it a quick twist or 2 to position the stinger for the next pass. The welder had a foot switch connected in place of the stinger's switch and the DC controller was either on the table or very close. I'd get everything ready, lower the hood, hit the 'run' button and the foot pedal at the same time. Two or 3 minutes later, I'd twist the pulley, then relax again.

Problems encountered: it was very hot weather, so I wasn't wearing a T-Shirt. The multiple layers of cloth where my shirt buttoned was adaquet protection, the rest of the shirt wasn't, so my belly got sunburnt. Also, the roller I.D. shrunk a bit, so most of them wouldn't reassemble onto the shafts. After trying to center one or 2 in the lathe so I could enlarge the bronze bushings by maybe .001", mostly right on the end, I came up with the idea of using a hand-held 3-cornered scraper. That worked great.

Borrowed use of a surface grinder to reface the thrust plates and replaced all the seals. It ended up costing me maybe $50.00 per roller instead of over $100.00/each for new. Some time later, I used the same setup for the front track idlers, but welded them up with hard-surface wire.

The outfit was used for several years to weld the "truck wheels" that supported the digging wheel on my trencher. A picture of a similar machine is here: http://mccormickequipment.com/for_sale/super_h_buckeye_tiling.html I think those wheels cost about a hundred bucks at the time; I could weld 'em up for a fraction of that, and seldom had to even bother turning them. If they were really badly out of round, I'd clean 'em up a bit in the lathe. Like the 'dozer rollers, the I.D. shrunk and had to be bored out a bit.

I did realize that running welding current through ball bearings was a no-no, but did it anyway. As I said before, those bearings are still OK for this purpose.

Bazz
01-22-2012, 10:04 AM
This set up is not very fancy but go very good ! for people with minimum space
Made it with scrap in 15 min,the pipe on the gear box is saw in the center and act like a spring collet .

http://i42.photobucket.com/albums/e344/Bazzshop/Milling%20attachment/IMG_0827.jpg

http://i42.photobucket.com/albums/e344/Bazzshop/Milling%20attachment/IMG_0822.jpg

http://i42.photobucket.com/albums/e344/Bazzshop/Milling%20attachment/IMG_0826.jpg