You can email your questions to Professor Hammer at email@example.com, or mail to Professor Hammer, c/o Classic Trucks Magazine, 1733 Alton Pkwy., Irvine, CA 92606. You'll receive a personal reply! We'll print your name and city unless you request otherwise. ron covell has made many DvDs on metalworking processes, and he 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 and their free catalog of DvDs. 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.
Q. I have made wheel tubs for my Chevy truck. Please give me your suggestion on the best method for welding these to get little to no distortion. They are 16-gauge steel, and we can weld them with TIG or MIG.
Via the Internet
A. Welding always causes distortion to some degree. The flatter the panel, the more troublesome the distortion will be. Unfortunately, with the wheel tubs you have constructed, there is a very long weld all along the edge of the flat side panel. You will probably get a considerable amount of distortion on the flat areas, no matter how carefully you weld the joint.
Still, some welding techniques are better than others for controlling distortion. Your best option is probably to MIG-weld the joint, one spot at a time. I can see that you have tack welds on the joints, holding the panels together. I'd suggest adding more tacks, until they are spaced no more than 1-inch apart.
After you've completed the tack welding, and the panel has cooled completely, I'd start adding one spot to the first weld, move about 8 inches, and add another spot to the weld there, move another 8 inches, and so on, until you reach the end of the joint. Wait until everything has cooled completely before continuing.
Then, you can add a little weld to the tail end of the first weld, move 8 inches, add a bit there, and continue with this pattern of slowly filling the unwelded areas, while keeping the heat in the panel to an absolute minimum.
Unfortunately, you'll probably still see some distortion in the flat areas, but by keeping the heat down, you will minimize the distortion as much as possible.
The next time you do such a job, adding even a small radius to the edges of the panels will go a very long way to keeping the distortion at a low level!
Q. I was pleased to read your comment in a recent column that in some situations plastic filler can be a better choice than lead. This speaks to an issue that often comes up where pros, hobbyists, and Mr. Know-It-Alls gather.
I learned to lead more than 40 years ago. I always found it tricky, time consuming, unhealthy, and costly. The results weren't always satisfactory, or long lasting; pin bubbles sometimes formed under the paint when untreated acid migrated to the surface. It is true that there are pitfalls that can accompany the use of Bondo too, like rust in the metal under the filler, poor adhesion, or color bleed-through in the paint.
These problems and several others can be traced to poor mixing of the product. It is true that there are health hazards with the use of Bondo; you have to wear a mask when you sand the stuff. I guess it might come down to a choice between lung cancer and heart or brain injury due to lead poisoning. Then, there is the economy factor. Lead is damn expensive compared to Bondo. A stick of 30-70 around here was going for $10 when you could find it. I may be preaching to the choir, but thanks for listening.
Michael A Figueroa
Via the Internet
A. Yes, the lead versus plastic filler issue is still controversial, with many proponents on each side. I think most of your comments are spot on, but I want to add a few tips that may help some others. Most plastic fillers are permeable to water, so if they are put over bare metal and the filler absorbs moisture, sometimes the metal under the plastic starts to rust. This problem can be alleviated by putting a sealing primer on the metal before the plastic goes on. Also, if the plastic is sealed with paint soon after it is applied, the paint film stops the moisture intrusion. Not all primers are good barriers to moisture, but the epoxy-based catalyzed primers are excellent moisture barriers, either on top of or underneath the plastic filler. These primers should stop color bleed-through, too.
You are correct that there can be health issues with careless use of both lead and plastic, but I consider lead by far the more dangerous of the two, since its toxicity is well documented, and it is absorbed through the skin. A simple dust mask should offer adequate protection from the dust created by sanding plastic filler.