Old Cebora Special Uno TIG issues

[Mark Harrison]

Hi, just got an old special Uno Tig from an auction. It has a foot pedal wired in along with a button on the torch. I have only used lift permanent live torches before. Thanks to folk here I swapped it to single phase and gapped, and cleaned the HF points to 8 thou. However the HF start seems really hot and miss, and the current seems to die quite quickly. I am sticking in 2T mode, pressing and holding the button, then pressing the footpedal, if and when it ignites. I have walked the current up, the scale has lost its markings and sticks at the bottom end. The Argon is the same as I was using for lift,but I would say the tip seems to oxidise faster even though I now have post time. Any suggestions to try for this simple DC mild steel setup? I had thought to purge through the argon gas side, and check for leaks .After that it may be the skip/ offered here as not working!

Cheers,Mark

 

[Mark Harrison]

think the gap it would need to produce would be no greater than 1/4". The ones that I used back in the 80's, you touched the tungsten to the work, lifted it then hit the pedal and that kicked on the HF. In doing this I think you could get by with 1/8" or less.

Just saw this on an electronic s forum, really do you do a non lift / HF start like that

 

[Mark Harrison]

Seems to be sorted by extra purging of the flowpath with Argon , and running more like 10Cfh at the torch. Cheers for Pete etc Al for the info on gapping and single phasing in. I cleaned ,the What I assume are ferrite electrodes )cores with some 3M diamond paper. Just like we use at work for ion optics. Cheers

 

[Pete.]

If the hf is a little hit and miss try closing the gap the tiniest amount (as in less than a thou). I found that mine was very sensitive to the points gap setting.

Oh and the scale is useless on 240V it reads double what you're getting. Wound right up you get about 100amps.

 

[Mark Harrison]

Cheers Pete, just swapping the ancient massive torch for a newish. Switch wires are the next challenge!

 

[Richard.]

Hf weakness can be resolved by a few simple things before getting involved with the guts of your machine.
First one is pre flow. Rather than turning your gas up to improve the hf just give it a second of preflow if the setting is there. This gives the hf a decent stream of argon to jump the gap. Next is as you rightly say torch. It’s quite common for old torches to cause a little bit or a lot of hf leakage. (Hf using another path to get to earth). I had this with 2 of my Machines where it was weak with the supplied torch and connecting up a good torch just transformed it into a great striker.
3rd is an internal hf leak. It can happen where instead of hf been sent down your torch it’s having a much easier life jumping the gap to earth inside of the unit. This can cause a catastrophic failure if that voltage makes its way to some delicate components on a board. Take off the covers and keep your torch well away from the internals. Turn off the lights and strike it up. If you see a spark jumping to earth inside it or if you see witness marks of this happening on one of covers you should take action to insulate this and hopefully direct the hf where it’s supposed to go. If all that fails then look into either gap settings or replace/repair.

 

[Mark Harrison]

Cheers Richard great advice. I'm getting there, but I will check again with lights off / and for witness marks. No adjustments on preflow, as far as I see. I find I'm just balling the mild steel rod off with a fierce wide arc. I'm going to adjust the gas down a bit. The same torch internals give a nice bead by lift tig on ewm arc machine. Beside that I will check for leaks, but after that I'm out of ideas.

 

[Pete.]

Sounds like you have the big switch set to AC or perhaps the HF is on all the time. Check both the big switch and the little switch are set to DC and check the torch and return are each in the correct socket. Torch on the right for AC next to the gas outlet.

 

[Mark Harrison]

Cheers, yes I wondered if HF was on all the the time. I had soldered in a new torch, so it's a possibility that it's holding it on. . I will check all the others, again. The new torch is a parweld so a bit more sophisticated than the old job. I basically flicked the switch and checked which wires broke/ made continuity and soldered them on. It had a foot pedal, on the same pins so I unsoldered that , for now. Thanks for the input. I will let you know what I find.

 

[Pete.]

Holding the button won't affect how the HF works. There are two modes - AC and DC. In AC mode the HF is firing all the time and you can hear it rattling away. In DC mode the HF fires for 3 seconds then stops.

 

[Mark Harrison]

Yes,sorry I meant had I wired it wrongly, or shirted it. Anyway I hadn't. You can see the HF switch off , I think it was a iffy tungsten I was using a blue generic multistrike, swapped for a fresh ceriated Binzel , and cleaned the steel again. All seems good thanks. HF is much better, it's arc from block to block , occasionally but not outside the block. Cheers

 

[slickrickladidadi]

Hi, just got an old special Uno Tig from an auction. It has a foot pedal wired in along with a button on the torch. I have only used lift permanent live torches before. Thanks to folk here I swapped it to single phase and gapped, and cleaned the HF points to 8 thou. However the HF start seems really hot and miss, and the current seems to die quite quickly. I am sticking in 2T mode, pressing and holding the button, then pressing the footpedal, if and when it ignites. I have walked the current up, the scale has lost its markings and sticks at the bottom end. The Argon is the same as I was using for lift,but I would say the tip seems to oxidise faster even though I now have post time. Any suggestions to try for this simple DC mild steel setup? I had thought to purge through the argon gas side, and check for leaks .After that it may be the skip/ offered here as not working!

Cheers,Mark

Hi Mark
I was just given that same model
but I am missing a torch with trigger or a pedal, do you know of where I might get one? or if you would be willing to sell me yours?

all the best