scratch type tig

Date 01-13-2002 17:32

Billy,
I assume "scratch tig" is a reference to how the arc is initiated. You physically have to touch the tungsten to the workpiece to to get the current to flow. This would be opposed to a GTAW machine that has high frequency capability, which, when turned on by a footpedal say, jumps across the tungsten-workpiece gap, without the need to physically touch the workpiece. Your less likely to contaminate the tungsten, and less likely to leave tungsten embedded it the base metal. Costs more money for the high frequency, as it is extra equipment.
Hope this helps.
Dale Simonds

By DGXL

Date 01-13-2002 18:00

Scratch type arc initiation is exactly as stated above. Lift start uses a voltage surge to start. High frequency uses a superimposed high voltage-low current circuit which may be used for starting or continuously. Practicing scratch starting helps.

For hobby type work, any of these work just fine. I've owned a primitive Lincoln AC/DC SMAW arc welding machine which was converted for a TIG set-up and it worked great, just no variable current (foot pedal/torch slider) while on the fly. Your limited to the type of current control of the machine (step or tap-types current control).

Thermal Arc, Miller, Lincoln and Esab all have small, economical SMAW/GTAW inverter type power supplies that work great and you can carry them around with one hand. They range from basic-no frills to all the bells and whistles you can use (pulsing, spot welding, etc.) Most operate on 120 Volt or 220 line power. If you have the money, look into these. If not, an old CC (constant current) DC arc power supply is easily converted to perform TIG welding. I own a 130 amp Thermal Arc machine now and it works great for hobby type projects, and it runs off the 110 v power in the garage. It has a pedal for variable current control.

By billy Date 01-13-2002 19:51

thanks for the responses.it sounds like i can do pretty much the same thing with either setup.what i don't want to do,is invest money in a set up and out grow it..i can get a lincoln tig with a pulser and everything min. the bttl. for around $1100...what would be the cost to buy a stick and convert it to have the same capablity..and what would you guys recommend i do..keep in mind i also want to weld alluminum..i build motorcycles out of my shop behind my house after work and on off days..this is a hobby now but would like to be full time..want to make my own frames,gas tanks,oil bags..ect...thanks again billy

By dasimonds (**)

Date 01-13-2002 20:18

Billy,
I your planning on doing Aluminum too, then you'll want the high frequency unit. Most people use AC for Aluminum, and with the current constantly switching back and forth, you'll need the high frequency running all the time to maintain the arc.
You might also want to consider something with a water cooled torch.
While the foot pedal is an excellent piece to have if your working at the bench, it can be rather troublesome if your welding out of position. You might have to run it with your knee, or some other body part. Not impossible to do, just rather dificult sometimes. But still a nice add-on.
Why buy a new machine and start converting it? I'd buy one that was already set up to do what you want.
Hope this helps.
Dale Simonds

By billy Date 01-13-2002 20:35

the only reason i was considering the conversion was the cost factor.not sure if i would really be saving much.to do alluminum with the scratch-i would have to buy the ac/dc machine --correct?thanks billy

By dasimonds (**)

Date 01-13-2002 21:50

Billy,
That's correct. You need the high frequency in combination with AC to weld Aluminum. With the high freq., you won't be scratch starting your arc. With the AC, the arc switches from + to - 60 times a second, depending on the frequency, 60 representing a 60 hertz power supply.
During the moments in between switching, there is no welding arc. I think the high frequency is an essential item for doing AC tig Aluminum. You also need the AC because it provides a cleaning action as it rapidly switches back and forth. I believe the cleaning action is removing Aluminum oxide, which forms instantaneously as the Aluminum is exposed to the oxygen in the air. As with other film protected materials, the oxide film that forms melts at a considerably higher temperature than the base metal. The AC helps to remove the oxide film, and the shielding gas keeps it from reforming by protecting it from the atmosphere.
I'm not sure if a square-wave( a supposedly instantaneous switching takes place) machine eliminates the need for the high frequency during switching or not, as I believe they came about to avoid the momentary power loss and difficulty reestablishing the arc.
But with the advent of all the new kinds of power sources, there may be something out there to replace AC for Aluminum. Maybe someone with more knowledge of the new power supplies will post something.
Hope this helps.
Dale Simonds

By DGXL

Date 01-13-2002 21:54

If this is the case, spend the $$ and buy a GTAW machine. You can DC weld the alumiunum with the right gas mix and technique, note this is not for a novice.

Your trying to get caviar with pizza $$.
Spend the $$ now and buy a used peice of GTAW equipment you won't outgrow any time soon. You can also stick weld (SMAW) and some will accommodate a "spool gun" wire feeder as well.

By dasimonds (**)

Date 01-13-2002 22:20

DGXL,
I'd be interested in hearing more about the DC Aluminum . Are you refering to a He/Ar mix? Or something more exotic?
I never had much luck with DC Aluminum. Isolated cases, such as the last day of a shutdown situation, 1 piece of handrail to fix, only DC machines available, scratch start GTAW torches, and straight Argon, that sort of thing.
Dale Simonds

By billy Date 01-13-2002 23:06

Dale and DGXL,thanks for the info and help.you guys have made up my mind for me.i am going to buy the GTAW machine.your help and time is appreciated..i'm sure i will be posting more questions when i get this thing to the shop..you guys have made my first visit to AWS a great one.by the way--any thoughts on welding 4130 chromoly tubing?thanks again billy

By DGXL

Date 01-13-2002 23:18

Hey B,
You don't ask for much do you? ;-]

DC GTAW is done on a daily basis in the aerospace/aircraft industries on nonferrous materials. You wouldn't have much luck with pure Ar. Yes a mix is used, typically with helium. Heavy weldments are easily joined without any preheat depending on the alloy. Beads are nice, fine with a good appearance and deep penetration.

By dasimonds (**)

Date 01-13-2002 23:29

Billy,
Check the Technical section, page 2. "Welding 4130 Chromemoly".
You might also try the search option.
Good luck.
DGXL,
Thanks for the info.
Dale Simonds

By - Date 01-14-2002 18:28

DCEN welding of Al is possible, but you need to treat the Al properly to remove the oxide scale, and weld it quickly thereafter to ensure that you weld before the scale re-forms.

Typically the oxide removal is done by a pickling treatment. This is not really an option for someone without the fancy baths and solutions.

While a fancy gas mix will obviously increase the heat of the arc, which is always a bonus when welding Al, the use of a hotter gas in itself will not make Al welding substantially easier with DCEN.

Regards
Niekie