Scratch Start TIG

Matthew L

Member
Hey everybody,
This will probably sound like a dumb question to the experienced/avid welder out there, but here it goes. Can you do scratch start A/C TIG? TIA, Matthew L
 
I'm not sure because my machine has a high frequency switch for starting the TIG. In my case the tungsten electrode never touches to actually be called a scratch. I would imagine that to contaminate the electrode.
 
Hello Matthew L


No arc should initiate without touching the work. tungsten tip should not touch. If it does, you need to stop and reshape the tungsten,

Guido.
 
What contaminates a tungsten on a TIG is dirt. Everything must be clean. I TIG'd in Nuclear Powerhouses.
 
You might check out weldingtipsandtricks dot com and weldingweb dot com. Covered extensively, check thru the archives of each.
 
The problem with scratch start for the amateur welder is you have about a 50/50 chance of breaking the tungsten off in your work each time you strike an arc. Now you have contamination in the weld and you also need to re-sharpen your tungsten. You'll very quickly get frustrated and give up. I suppose a good welder can do scratch-start (AC or DC), but most good welders have good equipment and have no reason to mess with scratch start.
 
Scratch start tig is still widely used in industry. D.C. Electrode negative is the preferred method, unless you have a high frequency box AC will not work very well and is used for aluminum.
 
We had a small suitcase DC tig machine that that had high freq, that also had a setting called lift start. You would place the point on the area you wanted the arc to start, pressed the pedal, and the arc would start when the tungsten was lifted from the surface. We would use it when we were repairing a small pit on a polished surface. It gave us the arc start, without the arc dancing around the ground portion of the tungsten.
 
I am totally amazed at the misinformation that is generated on this forum on welding and I try my best to stay out of these arguments, but I felt you needed a correct answer. Scratch start TIG is very common in the construction trades,but is used primary for Steel and Stainless Steel applications. It can be run by simply hooking up a TIG torch to any DC welder and running it on straight polarity. You will not break the tungsten by scratch starting it and you will not contaminate it if done correctly. You can strike the arc 2 or the inches away from the actual weld joint and carry the arc to the joint as not to contaminate the weld.I have made hundreds of X-ray welds on high pressure piping and boiler tubes with scratch start TIG. As for the Aluminum,you will need an AC machine with High Frequency to do a good job. The High Frequency not only helps establish the arc, it remains on while welding to stir the weld puddle and remove the impurities out of the metal. On the good TIG machines,which I have 2, this is an adjustable function. Some cast aluminum is so dirty, that sometimes you have to go over it 3 or 4 times melting the base metal and brushing it with a Stainless Steel wire brush to work the impurities out of it before you can actually add the filler rod. This is where the high frequency comes in. I weld Aluminum at least a couple of times a week and you never know what you are dealing with until you strike the first arc. A lot of what is out there is not Aluminum at all,but some alloy that just can't be welded.
 

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