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Sheet Metal Shaping and Bending

Learn the important difference between sheet metal shaping and sheet metal bending.

| June 2013

  • Sheet Metal Cover
    “Professional Sheet Metal Fabrication,” by Ed Barr, includes clear directions for using power and pneumatic hammers and the English wheel, as well as describing specific skills like hand-forming techniques, buck building, louver punching, edge finishing and more.
    Cover Courtesy Motorbooks
  • Sheet Metal 96-A
    To demonstrate the stretching effects of hammer blows on sheet metal, I will hammer a 7-inch-diameter panel of 20-gauge steel, beginning in the center and radiating out to the edges with overlapping blows.
    Photo Courtesy Motorbooks
  • Sheet Metal 101-C
    Before hammering the tucks flat, it is obvious we are moving in the right direction. The crimps along the flange have made the piece curve like the template.
    Photo Courtesy Motorboks
  • Sheet Metal 95
    I heated and modified two out of three identical 4-inch lengths of square steel stock to illustrate the effects of upsetting and stretching. The short piece at left was upset by hammering on its end. The long piece at right was stretched, or drawn out, by hammering its sides. The middle piece is untouched. These changes take place in sheet metal as well, though they are not so easily observed as here.
    Photo Courtesy Motorboks

  • Sheet Metal Cover
  • Sheet Metal 96-A
  • Sheet Metal 101-C
  • Sheet Metal 95

Professional Sheet Metal Fabrication (Motorbooks, 2013) is the number one resource for sheet metal workers old and new. Join veteran metalworker Ed Barr as he walks you through the ins and outs of planning a sheet metal project, acquiring the necessary tools and resources, doing the work, and adding the perfect finishing touches for a seamless final product. The following excerpt comes from chapter five, “Beginning Sheet Metal Shaping.” 

Buy this book in the Motorcycle Classics store: Professional Sheet Metal Fabrication.

Learning to form sheet metal by hand is the critical first step in your education in metal shaping. Machines are labor savers, but using them properly requires knowledge. Otherwise, they can transform perfectly good sheet metal into scrap with astonishing speed and efficiency. Fortunately, once you understand the basics of shaping sheet metal, its responses to your input will be less mysterious, so progress will come quickly—you will not need an arduous seven-year apprenticeship to start seeing results and finding satisfaction in your work. Furthermore, craftsmen have been shaping metal by hand for centuries, so do not be intimidated by the existence of complex and expensive machines, which simply harness electrical and/or hydraulic power to shape metal according to the very same principles you will learn here. For the average person interested in repairing rust spots and making a few patch panels for a historic vehicle, for example, a few basic shaping exercises will endow most enthusiasts with the confidence to move ahead with their intended project.

One overriding principle to keep in mind when working with sheet metal is that you often trade thickness for surface area as you shape the metal. Sometimes you increase the surface area, or stretch the metal, making it longer and thinner. Other times you will decrease the surface area, often called shrinking or upsetting, making the metal shorter and thicker. I tell students to think of their metal as a slab as you manipulate it. If you were to mash down with your thumb in the middle of a pie crust, for example, you know instinctively that the crust would get very thin under your thumb as the dough compressed. If you mashed the crust a few times in close proximity, the entire crust would spread out ever so slightly as a result. Metal doesn’t behave exactly like a crust, of course, but I think this image makes it easy to understand how to change the shape of metal by influencing its thickness.

Bending Sheet Metal

Metal can be shaped without changing its thickness as well, such as when you bend it in a vise. Think of a bend like a fold in a piece of paper; the metal is creased along a single axis. The bend could be sharp, like when you hammer a piece of metal over at 90 degrees, or the bend could be gradual, like when you bend metal around a large pipe. Perhaps at a microscopic level the thickness of the metal is influenced very slightly, but for our purposes think of the bend/fold as a change of shape that does not change the thickness of the metal. The bend or fold is easy to understand and easy to forget. Once you start shrinking and stretching, it is easy to think only in those terms, but the concept of bending is just as important as shrinking and stretching; many shapes cannot be made without bending.

I recently learned two terms from metal shaping legend Fay Butler that perfectly embody the concepts of shaping metal by changing its thickness and forming it without changing its thickness. According to Butler, shape and form were used by men such as Scott Knight and Red Tweit at the now defunct California Metal Shaping to differentiate between two distinct modes of working. Out of respect for the tradition of shaping started at California Metal Shaping, and in an effort to develop standardized terminology among metal shapers, Butler continues to use the terms. I, too, will use shape to refer to a process involving a thickness change and form to refer to a process that does not involve a thickness change.

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