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  #11  
Old 05-24-2010, 10:02 PM
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No loss of arc
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  #12  
Old 05-25-2010, 12:06 AM
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Earlier someone made a weld positioner and used a rotor off a car and a copper shoe to rub on. it supplied the ground without going through the bearings.
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  #13  
Old 05-25-2010, 07:49 AM
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What I liked was the idea of turning it with your feet while you weld.
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  #14  
Old 05-25-2010, 10:01 PM
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Neat line boring rig.

Nice rotator/weld positioner too.

Grounding is a subject of great debate, but the fact remains that almost every mobile welding rig hereabouts has a doodad like you're building with the axis of rotation horizontal rather than vertical. They're used for "spool welding" up piping pieces, and usually have a faceplate hacked out of a scrap of plate to fasten the work to. Some guys like to advertise their occupation and drive around with this doodad clamped in the vise on the corner of their welding deck.

Grounds are not generally done through rolling elements bearings as the bearings tend to pit and become rough with time. Most of the git'er done crowd (me included) use a simple collar on the main shaft with a flag welded on to clamp the ground cable to. The most sophisticated ones use a spring loaded copper or brass shoe for a contact, but those are not the norm, by any means.

FWIW, this is what I've seen on mobile units using stick for rods from 1/16" to 3/16"; welding currents on the order of 50 - 200 amps.
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  #15  
Old 05-26-2010, 02:36 PM
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see it's stuff like this that just shows me you guys are really cool. I mean how many out there are doing this kind of stuff on a whim?
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  #16  
Old 05-26-2010, 09:30 PM
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Here is a picture of the boring bar tool holder insert. This is only a short leftover piece, couldn't find any new ones.

It has a 9/16" OD and holds 3/8" square bits and new ones are several inches long. The ends are tapered a bit to help with the press fitting in the hole. We made a jig with an old 3/8 tool to keep it square when installing.

Still haven't found them online and not sure where we got these new.
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  #17  
Old 05-26-2010, 09:56 PM
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I snuck out to the shop this evening. Since I had some decent ideas for a sliding ground I thought I would see what I could accomplish.

I put my meter on the rig and found the resistance going through the bearing varied from 0.4 ohms stationary to 1.5 ohms while rotating.

I used some 1/2 in bar stock to make up a teeter-totter to hold a scrap EDM electrode (Pic 1 & 2). I slotted the hole where the electrode sits and beveled the plate. As the electrode wears, it can tilt and continue to ride flat on the bottom of the table.

I rechecked the resistance and it was 0.1 ohms sitting still or rotating. I don't know if the decrease in resistance will improve the arc, but I feel better about not running current through the bearing.

Next, I plan to build an adjustable rest for my arm or the gun, so I have something to steady against.

Quote:
Originally Posted by camdigger View Post
Grounding is a subject of great debate, but the fact remains that almost every mobile welding rig hereabouts has a doodad like you're building with the axis of rotation horizontal rather than vertical. They're used for "spool welding" up piping pieces, and usually have a faceplate hacked out of a scrap of plate to fasten the work to.
What is the advantage of having it horizontal?

Quote:
Originally Posted by Pyro J View Post
Here is a picture of the boring bar tool holder insert. This is only a short leftover piece, couldn't find any new ones.
Thanks. I searched for "square hole bushing" in Google and found Stock Drive Products has them in threaded, unthreaded and split.
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Last edited by TriHonu; 05-27-2010 at 10:07 AM.
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  #18  
Old 05-26-2010, 10:36 PM
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Looks that'll work but I wonder - since your ground is not isolated from the bearings, will you still be passing some current through them via the framework, etc.?
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  #19  
Old 05-26-2010, 11:26 PM
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Quote:
Originally Posted by cutter View Post
Looks that'll work but I wonder - since your ground is not isolated from the bearings, will you still be passing some current through them via the framework, etc.?
You are correct, with two current paths, the fixture will act as a current divider. With .1 ohms and 1.5 ohms at 100 amps, 93.75 amps will go through the copper electrode and 6.25 amps will go through the bearing.

The question is whether arcing would take place at the path of least resistance or at the point of the closest gap? My hope is that the copper, with a much larger surface area, should always have contact with the table and eliminate any arcing. I looked under the table while making a test weld and could not see any arcing at the copper electrode. Maybe someone with more electrical knowledge will chime in?

I could put an insulator between the teeter-totter leg and the plate or isolate the table from the shaft.
Now you got me going...

Last edited by TriHonu; 05-27-2010 at 10:10 AM.
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  #20  
Old 05-26-2010, 11:49 PM
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Would it work to isolate at the swivel bolt with a plastic tube on the bolt and a plastic washer on each side of the grounding lever?
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