Welder earth/return through bearings?

[hotponyshoes]

I am just having some initial thoughts on making up a jig for butt welding 2 pieces of tube together.

My first idea is to fit 2 ball bearings into a vee bracket. Make 4 of these up and fix them to a length of box section.
Add a torch holder/positioner and then I can lay the tubes onto the bearings and rotate it under the torch.

First question- can I use the bearings as the return path for the welding current?
Ie. Just put my earth clamp onto the frame?

Initial section is going to be 25mmx1mm 304 tube but I would like to build it to handle bigger tubes and may want to use some ac for alloy.

Was thinking of using stainless bearings but only because it will be stored in a damp workshop.
Also thought, as it's low speed imay be able to get away without greasing the bearings which may or may not be better if i am using them as a earth path?

Will this work or will I get arching across the balls in the bearings?

 

[123hotchef]

great idea I think the bearings may lack surface area for the earth return give it a bash though you may be surprised

 

[AndersK]

Even a 12 V system is enough to get arc gouging thru bearings.
You might get away with it since you'll be on low load and low rpm though.

 

[rtbcomp]

I wouldn't do it, as said you risk gouging the bearing or even welding them up. Use a block of copper as a brush to rub against the tube, or have a long return lead so you can rotate the tube without it tangling up, could get a bit messy but will give the best connection.

I've heard of gearbox/diff bearings being damaged when an engine earth has come adrift.

 

[hotponyshoes]

I will do a bit more thinking!

What's best- earth both pieces of tube or just one of them?

 

[rtbcomp]

You should get away with earthing one, just make a bridge between both pieces when you start.

 

[colnerov]

Hi, Put a length of bare heavy cable looped loosely round the tube and held together by the earth clamp, the weight of the clamp will maintain contact. Copper braid would be better because bigger surface area.

Colin

 

[AndersK]

Hi, Put a length of bare heavy cable looped loosely round the tube....

That is a good advice that can be used in various situations

 

[TechnicAl]

Look at welding positioners.... they have some sort of rotating earth

 

[rtbcomp]

^^ Probably a slip ring

 

[Shox Dr]

Look at welding positioners.... they have some sort of rotating earth

I used flat braided copper wire, kept under tension with a spring

 

[brightspark]

post 11 the best braded copper wire under tension. through the bearings it will kill them in a few seconds. hardly any contact greasy and a poor conductor

 

[Shox Dr]

 

[Anguz]

Got room for something like this? I hadn't got my mug with me for scale... I have more than one if you want a few

 

[hotponyshoes]

I have got the space for it!

Do you think 1 or 2 of those would work?
Will they need to be profiled to the tube?

I suppose I could mount one by the bearing so it makes contact just before the tube touches the bearing, may be one each side as they would be in a motor?

 

[Anguz]

Would think at least 2, one each side..not sure how much current they woukd take before you cooked them
But the holders are brass (ish) so wouldn't only be the brush pigtails taking the current
I have spare brushes as well..
Wanna try some?

 

[hotponyshoes]

Yea I will give some a go!

I have got a mate sorting me out some braided copper but ideally I wanted to just drop the tube in and tack/weld. Some of the bits will only be a couple of tacks so I have been trying to think of a quick way to attach the braided copper. These might be a better option, I can try passing some current through them before I get them mounted!

 

[Anguz]

At work now..pm me to remind me