Q: Hi, Ron. I have been using my new TIG welder, a Miller Synchrowave 250 DX, which is a beautiful machine, but I'm having a couple of problems.

I have been welding 22-gauge steel and using the TIG hammer-weld process. I enjoy it a lot, and I probably won't pick up the acetylene torch again. I have been using 3/32-inch-diameter 2 percent thoriated tungsten with 30 to 40 amps set on the machine. I'm using DC, electrode negative-is that what you suggest? Should I be using water to shrink the welds after hammer work? Should I be using smaller tungsten? Miller says to use the smallest possible for the amps needed for the weld. It seems to work so far, but I don't know if smaller tungsten is better.

Also, I tried to weld some aluminum and I have had poor results. You would not be proud of these. I used pure tungsten, 3/32-inch diameter, 100 amps, AC, with the high frequency set to continuous. The metal would form a puddle, but I had problems getting the material to join together to make a weld. Possibly I didn't clean the metal well enough, and there was contamination at the joint? Should I use 2 percent ceriated tungsten with a sharp tip? Miller says this is the new technique-what do you think?

I'd like to know where you get your killed steel sheets for metal fabrication work. And finally, what kind of aluminum do you use for bodywork?
Jonny McCormick
Parks, Arizona

A:Your machine settings sound fine! I don't recommend chilling the welds with water because it hardens the metal, making it more difficult to work with a hammer and dolly. Many welders prefer using smaller tungsten diameters when welding steel sheetmetal-you could probably go as small as .040-inch diameter if you wanted to. My opinion is that the shape and focus of the arc is determined more by the sharpness of the point on the tungsten, and that the tungsten diameter isn't much of a factor. I put a point on the tungsten at about the same angle that a pencil sharpener puts on a pencil. There certainly are some advantages to using smaller tungsten-it's less expensive, and it can be resharpened more easily. I do most of my welding with 3/32-inch tungsten, so I can weld both steel and aluminum without having to change the tungsten.

For welding aluminum on a square-wave machine like yours, the proper setting is AC with the high frequency set to continuous, so you are on the right track here. Pure tungsten is preferred for welding aluminum that's over 1/8-inch thickness, and in this case you would form a ball on the end of the tungsten. It's easy to form this ball by running a short burst of current through the electrode when the machine is set to the reverse polarity or electrode positive setting. Just as a point of interest, the latest inverter-style welding machines don't require balled tungsten, even for welding thick aluminum, and you wouldn't use pure tungsten unless you wanted to use a ball on the end!

For welding thinner aluminum (which is what I think you are talking about), I prefer using a rare earth tungsten-either ceriated or lanthanated-and I like to use the same sharply pointed tungsten configuration for aluminum sheet as I do on steel. Rare earth tungstens have some advantages over thoriated for welding aluminum (thoriated electrodes have a tendency to split, and they are slightly radioactive), but any of these will work for aluminum sheetmetal. One additional benefit of the rare earth tungstens is that they don't seem to get contaminated as frequently as the thoriated electrode.

Cleanliness is important with ANY welding process, and TIG welding is perhaps more sensitive to surface contamination than any other process. Do whatever it takes to make sure the metal at the joint is squeaky clean. It needs to be free of paint, corrosion, oil, and all other contaminants. I usually sand any material that has visible contamination, then wire-brush the joint with a stainless steel toothbrush and wipe it down with acetone just before welding.

You need to flow more argon for welding aluminum than with steel-I generally use 12-14 CFH for steel and 16-18 CFH for aluminum. If you hold the torch too far from the base metal, that can cause problems too, since the argon may not shield the puddle sufficiently, and it makes the puddle larger and more difficult to control, too.

Drawing-quality steel is difficult to get in small quantities. I have a friend in Apache Junction, Arizona, who sells this material, and I believe he will ship it, too. You can contact Ron Middaugh at 480-209-3426. I use 3003 H-14 aluminum for most of the work I do.A good mail-order source for this is Aircraft Spruce (877-477-7823, www.aircraftspruce.com).

You can e-mail your questions to Professor Hammer at covell@cruzio.com, or mail to: Professor Hammer c/o Classic Trucks Magazine, 774 S. Placentia Ave., Placentia, CA 92870. We'll print your name and city unless you request otherwise. Ron Covell has made several metalworking videos and offers an ongoing series of workshops across the nation covering all aspects of metalworking. Check them out online at www.covell.biz, or call for a current schedule of workshops or their free catalog of videos, books, and fine-quality metalworking tools. Phone 800-747-4631 or 831-768-0705. You can send a request by mail to: Covell Creative Metalworking,106 Airport Blvd. #105, Freedom, CA 95019.