You can email your questions to Professor Hammer at email@example.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 many DVDs on metalworking processes, 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 and their free catalog of DVDs 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.
Q. I have a '46 Chevy ice truck. The box has a grid framework, and the skin is flat. What is the best way to attach metal to the frame-is it better to glue it or weld it (I have a MIG welder)? I am concerned about hot and cold movement. And what is the best way to get a heat wave out of the metal?
Via the Internet
A. Welding always causes some distortion, and that's especially true for large, flat panels, like the sides of your truck. There are some great adhesives made for just this purpose, and they are being used more widely in industry all the time. Many ambulance bodies have metal skins that are bonded to the inner structure, and adhesives have been used in the aircraft and auto racing industries for many years.
There is non-expanding foam designed for bonding roof skins to the inner bracing used in delivery vans, and this is available from automotive paint stores. You can buy bonding foam adhesives from "big box" stores, too, but for this application, I'd get the automotive grade, even though it's more expensive.
If you have a large, flat panel that is distorted from being welded to an inner structure, that's very difficult to fix! The distortion is caused by the weld area shrinking, and the way this distortion is normally fixed is by hammering on-dolly, right on the weld. This is possible with single-thickness metal, but when there is an inner structure in the way, you really can't get the dolly where it needs to go to properly back up the hammering. About the only fix for this difficult situation is to shrink down the highest waves and use plastic filler to hide what's left.
Q. Hope you don't mind a question coming out of the blue! Our previous communication was 2 1/2 years ago; I guess it's been that long since I attended one of your weekend workshops. Time flies!
I have a crease in the door of my '57 Chevy, which I am currently stripping in order to paint. Needless to say, it is full of Bondo, and has many areas of body damage needing repair. I would like to use some of the skills you demonstrated in your workshops and DVDs (I own them all) to eliminate the need for much of the filler.
Sargent's book Autobody Sheetmetal Repair, which I assume is much the same as The Key to Metal Bumping, since they were written by the same guy, talks about applying heat to the crease and roughing it out with a dolly from the backside. This leaves two "ridges" alongside the original crease location that get dressed down by off-dolly hammering. I recall a demo you did where you whipped a piece of sheetmetal that you had domed with the wheel. At no time did you apply heat. The hammer and dolly work were much as Sargent had suggested, but I am sure you did it all cold. What dictates the necessity for heat to be used on a crease? Is heat "better" than no heat or vice versa? Does the depth or "sharpness" of the crease have a bearing on whether heat should or should not be used?
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A. Ken-always good to hear from old friends! I grew up with Frank Sargent's books-he wrote the textbook I used in the collision repair classes I took in the 1960s. As much as I respect his skill and knowledge, I do have a different take on the use of heat. Heat is "big medicine" in my world. In almost all cases, I try fixing the damage at room temperature first, and if it simply can't be done that way, then I resort to applying heat. In many cases, adding heat will add problems of its own, which could easily outweigh the problems that were there originally.
Sargent is the one who taught me that to take out a crease, you start at the ENDS of the crease and work toward the center-definitely do not start in the center! Be sure not to overlook this crucial point.
Q. I am not sure if you can help with this question, but I was wondering what grade of steel would be most appropriate to use in the construction of a ladder frame chassis for a '57 Chevy pickup. Though I have read lots of information regarding this matter, I have not found a source that gives clear guidance as to what would serve this purpose best.
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A. I presume you are talking about using rectangular tubing, rather than round tubing. With rectangular tubing, you really don't have a lot of choices with the alloy-it will pretty much all be "regular" mild steel, normally designated 1018 or 1020 steel. In the world of round tubing, you may have some other choices (such as ERW, DOM, seamless, or chrome-moly tubing). For street-driven vehicles, I'd suggest staying with mild steel in all cases-that's what the original manufacturer used!