TIG scratch/touch/lift start difference?

Date 11-19-2002 11:29

Lift is different than scratch or touch. It is a product of the welding machine sensing the tungsten shorted when the pedal is depressed and when you lift the tungsten the main load contactor is closed.
This prevents contamination of both the tungsten and the weld.

By DaveSisk (**)

Date 11-21-2002 20:03

So, with "lift start", you don't actually touch the tungsten to the workpiece? Or did I misunderstand?

Thx,
Dave

By Lawrence (*****)

Date 11-21-2002 23:40

Scratch start in essence is a "hot" electrode that is at full power when contact is made. Scratch starting with a very sharp pointed electrode or with an electrode less than 3/32 inch dia. will in most cases leave significant tungsten residue, which in many cases is unacceptable.

Lift start is a more high tech option which employs special circutry, allowing the machine to recognize when the tungsten is lifted from the workpiece, igniting the arc and sloping up with full power only after contact with the work is broken. In theory this leaves less tungsten residue and is quite handy when one cannot lug a foot pedal up a scaffold or some other difficult reach place. Still there is a risk of contamination with lift start when compared to high freq. or inverter style arc starting systems.

So to be clear here is the order of prefrence for GTAW arc starting from worst to best.

1. Scratch start.... Hot (fully charged) electrodes have many disadvantages.

2. Lift start. Nice option for field work when a foot pedal is not easily available.

3. and best... High Frequency or Inverter arc starting. These two when employed properly initiate the arc with minimum risk of contamination.

By DaveSisk (**)

Date 11-25-2002 04:02

Lawrence, please tell me more about the "inverter-style" starting you mentioned in your post. Is this what I see sometimes called "hot-start" with inverters?

Thx!
Dave

By Lawrence (*****)

Date 12-02-2002 22:59

Dave,

Sorry for the tardy responce.

No, inverters are not a "hot start option" thats yet another thing.

http://millerwelds.com/pdf/techart/choosingTIG.html

The above is a good link, not too technical. For regular shop work High freq. and Inverters are equal. But as competition becomes more fierce (and it is) Inverters and the whistles and bells may become affordable.

The inverter on my Miller Dynasty ($3500) is hands down superior to the HF/DC+pulse Joke of an arc starter on my Miller Aerowave ($8,000). Now the Miller Synchrowave 351 (Over $3,000) has nice smooth power but high quality low amp HF arc starting requires adjustments of internal potentiometers every few months~~which is a huge pain and not a thing you want your line welders messing with. Finally the Miller Synchrowave 250~~ (cheaper than the rest) We have had some these babies over 13 years and never have they been a problem.

So whats the moral of the story? High tech is not always the best choice (just ask Ed Craig) This is especially true with low amp GTAW (under 20 amps). Do alot of research and ask alot of questions. Visit your dealer and demo them all, next try your local technical college and ask about how the machines have proven themselves over time, this is not a thing you can find out with a factory demo.

Thats my rant for the day

Lawrence