Rotating tube jig - completing the MIG circuit

[Keith_]

Hi All,

Long time lurker.. first time poster. Firstly, I would like to thank all of those that I have learned a great deal from on these forums.

I'm looking for a solution to a rotating tube/flange welding jig. Flanges are welded each end to a 4m length of tube. The tube is supported, at thirds, by two sets of rollers - one set has a small dc motor that rotates the tube. As can, hopefully, be seen in the pics. It works "okay" at the moment and produces nice welds. The problem is I have a steel disc as the drive wheel attached to the motor and was using the contact between the disc and the tube to complete the welding circuit. The wheel started getting a lot of pitting due to the high current and small contact area which meant the tube started to slip - not good. The same pitting happens if the power goes through the bearings too - and the bearings start to get a bit "crunchy".. I assume the bearings and races are getting a lot of pitting.

I want to use a rubber wheel or something to drive the tube but also avoid routing the power through the bearings.. have thought about slip rings and brushes.. perhaps a copper strap that loops over the tube that the negative can connect to. Was wondering if anyone has come across a decent solution to this type of problem? Any thoughts greatly appreciated.

Thanks all.

 

[Wozzaaah]

Why not just put the clamp on the tube then move it to the flange once you've welded it and do the other end?

 

[Welderpaul]

Like Woz says, just stick the clamp in the end of the tube.
If it's only going round once the cable won't get tangled.

 

[gordon stephenson]

If the tubing was clean enough you could wrap it with a section of earth lead that had the insulation removed and held firm onto the tubing by spring pressure etc.

 

[Wallace]

Expanding on Wozzaah and Welderpaul, perhaps if your earth lead is long enough suspend it from above so when disconnected and left to hang the turn unravels.

 

[500e]

Soft braided earth strap with a spring loaded clamp (expanding rather than contracting)that fits inside tube, easy to make easy\quick to fit & remove.
Other end to a strong point then normal earth clamp, no mod to welder

 

[pedrobedro]

A strip of brass or copper sprung so it stays in tension against the tube like the systems used in car steering wheels for the hooter.

 

[Tino]

Like Woz says, just stick the clamp in the end of the tube.
If it's only going round once the cable won't get tangled.

I hadn't seen this thread, but I've just put some photos in my album doing more or less this very thing. I tack the earth close to the centre role it back then role and weld the other way. Only difference is I get to do it by hand.

 

[Keith_]

Thanks for the suggestions - can't simply clamp onto the tube end or flange because the tube needs to be able to rotate without me having to worry about shutting the motor off/cable twisting etc. Think I'm going to make a spring loaded copper brush that sits underneath the tube, mounted just off the slave rollers, so I can just put any size tube on and not have to mess around connecting things or turning things off. Cheers.

 

[armalites]

What about a piece of copper braid or stripped battery cable with a spring on one end and tethered to the jig on the other end. You could then just pull it over the top and hook the spring to the jig. If you had multiple hooking holes then it would cater for different size pipes.

Certainly getting some nice looking welds with the jig.

 

[BillJ]

Have a look at these - they have both solved similar problems:
http://www.mig-welding.co.uk/forum/showthread.php?t=36516
http://www.mig-welding.co.uk/forum/showthread.php?t=17540

 

[backpurge]

Can you not stick a rotating earth clamp on the end of the job

 

[Keith_]

@BillJ - post #11

Thanks for the links.. looks as though Robotstar5 knows what I'm looking for.. have PMed him.

 

[the snooper]

what you need is a clamp to attach to the pipe with a bearing to stop the cable twisting up and slip rings and brushes to transfer the power to the clamp it wont matter that the clamp would be off centre if you support the weight of the cable to stop any drag