You can email your questions to Professor Hammer at firstname.lastname@example.org, 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. Our Tubing DVD is informative and enjoyable, and I learned some new things, too. My question is about working with tubing that has a welded seam: Do you pay any attention to the location of the seam when bending, particularly with square tubing? I'm wondering if the seam is harder (or possibly softer) than the rest of the metal? Is there any likelihood of the seam cracking or splitting? How about the faces of the square tube that deform inward as the tube is bent, does the welded seam resist this movement?
Thanks for your time, Ron. I'm looking forward to watching the Shaping Aluminum with Hand Tools DVD.
A. Electroweld tubing is a very high-quality product, and I've never had a seam split when bending it, so the integrity of the welded seam isn't usually an issue. The weld does protrude inside the tubing, however, and the additional mass of material at the weld will cause that wall to behave a bit differently than the rest of the tube. For this reason, it's preferable to orient the welded seam on the side of the bend, rather than the top or bottom, to get it close to the neutral axis of the bend, where the metal is neither stretched nor compressed. This is not a hard and fast rule, and in fact, if you look at many exotic chassis made from round tubing, you will commonly see one piece of tubing that has bends in many different directions, so of course the seam can't be on the side of all the bends.
As I mentioned in the DVD, square tubing is made by pulling round tubing through a square die, and if you examine several lengths of square tubing, you'll see that the position of the weld is not consistent. It seems like they try to keep it centered between the corners, but there can be a lot of variation, and I've occasionally seen the weld wind up very close to the edge of the tubing. If the weld isn't centered, I'd place it closer to the inside of the bend, where the metal is being compressed, rather than toward the outside, where the metal is being stretched.
There are many other factors to keep in mind when bending tubing, but the welds are made with very sophisticated equipment, and each batch of tubing is closely inspected to spot any problems before it leaves the mill.
Q. Ron, I read your column each month with great interest to see what bits of wisdom I can gain. Some time ago, you wrote about slapping files, and how you thought they didn't really shrink the metal. I recently purchased a shrinking hammer that has grooves in it similar to a file.
Should this hammer be used on-dolly or slightly off-dolly? I have been told that I should strike the metal with a glancing or sliding blow instead of hitting directly. I have seen a similar hammer with a head that rotates with each blow, but that seemed more like a gimmick than a functional tool. Thanks for any advice.
Via the Internet
A. Hi Tom, glad to hear you enjoy my column!
In the world of metalworking, you'll find that different craftsmen have different preferences. I don't personally use "shrinking" hammers. I've tried all types of shrinking hammers, and my opinion is that they don't shrink the metal any better than a smooth-faced hammer. I've done side-by-side tests to learn more about this, and until I see some evidence to the contrary, that's my story and I'm sticking to it!
Certainly, if you strike on-dolly with a shrinking hammer, it will stretch the metal. In many cases, if you strike off-dolly with a shrinking hammer, the metal will shrink, but this is often true with a smooth-faced hammer, too.
My opinion is that the use of a glancing blow is optional. I hammer with a glancing blow because that's the way I learned from the guy who first taught me, but when I concentrate, and hammer straight up and down, the result seems the same to me.
Readers, please let me know if your experience differs from mine-I'm always interested in learning something new about metalworking!