“Shrinking” sheet metal refers to shortening an edge of the sheet, thus forcing it into a radius or curve. Commercial shrinker/stretchers clamp the edge between pairs of jaws that are then drawn together to shrink it or pulled apart to stretch it. The shrinking action creates small “tucks” in the edge, and this tucking process can also be accomplished manually by placing the edge between parallel metal fingers and then simply twisting it. The more tucks you form, the greater the shrinking effect. The round, tapered ends of steel drift pins are perfect sources for these rigid fingers.
Constructing the Manual Tuck Shrinker
Weld the wide end of one drift pin to the center of a 1/2-inch by 2-inch edge of one of the pieces of the flat bar stock using the arc or MIG welder, positioning the drift pin so that one of its tapered edges is parallel to and even with one of the 2-inch flat edges of the flat bar. Weld the second drift pin to the second flat bar in a like manner.
File the welds using the mill file until the welds are even with the 2-inch flats of the bar stock.
Cut a 2-by-4-inch piece of sheet metal using the tin snips. This sheet metal should be of the same thickness as the metal that you will be shrinking.
Sandwich the 2-by-4-inch piece of sheet metal between the two pieces of bar stock with the drift pins slanted toward each other. The space between the parallel edges of the two drift pins will be the same as the thickness of the piece of sheet metal that separates the two pieces of flat bar.
Secure the sandwiched assembly in the jaws of the bench-mounted metal vise.
Using the Manual Tuck Shrinker
Position the sheet-metal edge to be shrunken between the two drift pins and twist it until a small tuck is formed.
Flatten the tuck using the auto-body hammer against the anvil portion of the vise.
Repeat the tucking-flattening process until you have achieved the desired edge radius or curve.
Mastering this traditional technique for tuck shrinking sheet metal is a classic case of “practice makes perfect,” but once you’ve gained experience with this simple tool, you will find it an indispensable addition to your sheet-metal shop.
The raw edges of sheared sheet metal can be very sharp. Always protect your hands and wrists with gloves made specifically for metal working. Protect your eyes with safety goggles and your hearing with NRR-rated ear muffs whenever shaping, grinding, cutting or hammering metal. Observe all standard safety precautions when using welding equipment, including use of a welding helmet and welding gloves.