scratch start ?

[Blown S-10]

what are the drawbacks, and benefits(probably not any), of scratch starting TIG ? mild steel, stainless & aluminum(mostly)

[dyn88]

scratch starting aluminum is a big nono as you will instantly contaminate the electrode. The only problem with scratch starting any dcen process is that as soon as the arc is initiated any of the electrode that may break or chip off is going to end up in your base material. This isnt a problem on auto body or other non criticle joints, but you will possibly fail testing due to contamination. all in all though lift start or high freq are the best ways to go.

[Blown S-10]

lift start ? i thought that was the same as scratch start, just different terminology

[HAWK]

Blown S-10,

Benefits: No additional equipment required. Torch with valve and shield gas.

Scratch start is limited to DC. Tungsten contamination in the weld prohibits use for critical work as dyn88 mentioned. You can start the arc on a nearby piece of carbon and drag it to the work piece, but you may still get carbon contamination. I have never used scratch tig for any radiographic test. HF and "Lift Arc" starts are X-Ray quality starts. From there it is up to the operator.

Word to the wise. If your machine is capable of "Lift Arc" or some form of touch start, do not use scratch start unless there is a specific function for it on the control panel as there is on the Miller XMT 304 and ALT 304. Otherwise you may damage your machine.

[JTMcC]

To steal a line from the cosmos guy in the 80's, there have been billions and billions (and continue to be today) of critical stainless, monel, ect. pipe welds made, to the strictists(?) x ray requirements on the planet, with scratch start tig. I've personally watched hundreds of welders qualify, and make production welds with scratch start tig, many on old SA-200 engine drives. This in everything from nuke powerhouses to natural gas pumping stations to chemical plants. My grandfather spent years in the nuke bomb plants, from Oak Ridge to the Savanna River Project, happily making tig welds with scratch start. This was under some of the harshest weld inspection ever. The same goes on today.
Aluminum, of course, is a whole nuther animal.

JTMcC.

[Tinker]

My very first tig experience was scratch start and I found it pretty frustrating. Kept sticking the tungsten and even using a copper strike plate made it only a bit better for me. Of course my inexperience and the fact that I rigged a cheap 17V torch up to my 120V MIG might have made things a bit more challenging

Did manage to modify an intake manifold for our VW sandrail and make a few things before starting my first real welding class and trying a real tig machine (Dynasty 300's). Needless to say I couldn't go back to using my jury rig tig/mig again. Using a real CC source might have made a difference but after using lift and HF start I didn't want to go back to scratch. Couldn't justify even the Dynasty 200 for hobby work at the moment but I'm real happy with my cheap eBay T/A 250 GTS. Would have liked AC but it's got everything else (including the lift and HF start) I need at the moment.

Tig is neat

[walker]

Just curious, does the TB have a lift arc option???

[HAWK]

Walker,

No "Lift Arc" on the TB. The Miller Pro 300 Diesel has the "Lift Arc" DC tig. You can power a Dynasty 200 from the TB aux power and get the "Lift Arc" tig. The Lincoln 250 also has a touch start tig. It is a sweet machine, but too new and too many dials for me to trust.

[dyn88]

lift arc and scratch start are different operations all together. lift arc start works by constantly sensing for a short circut to occur in idle mode, then at a preset amount of time after the short the electrode goes hot. Scratch start has the electrode hot all the time, and initiate arc by creating a short circut. Another disadvantage to scratch is the decreased life expectancy of a nice sharp electrode(which I find to be a necessity when welding sheet thinner than .031)

[fun4now]

lift arc

go to this link it is on the miller site under the dynasty 200 go to the part on lift arc and hit the video. it is a simple cartoon type so it loads quick and it will show you lift arc

http://www.millerwelds.com/products/tig/dynasty_200/

hope this helps