Make Your Own
Turn scrap metal into a powerful panel-shaping machine
Build a deep shrinker/stretcher.
There are five things you can do to a flat sheet of metal to transform it into a car body panel: cut, weld, bend, shrink and stretch. It’s the latter two that really turn 2D into 3D. To add double curvature, or ‘crown’, you’ll need to stretch central areas and/or shrink peripheral areas. Enter the deep shrinker/stretcher: a quick, quiet and cost-effective method of putting the basic shape into panels.
There are three types. The first is a large version of the small shrinker/stretchers that are now widely available – and they use the same jaws as the small machines. They generally have an 8in throat and cost around £265. The second is a type made popular by Lars Jansson in his excellent videos (lazzemetalshaping.com). They have two moving jaws, a 6in throat and cost about £350. The last type are industrial machines, which allow for greater capacity and powered operation, but cost thousands.
The first type can create more crown over a wider area due to its frame’s greater height and depth. However, its fixed jaws mean the metal gets lumpier and can snag when repositioning. The second type technically has a smaller capacity, but this is countered by its two moving jaws, which make its more versatile.
Off-the-shelf machines are fine, but you can make a better one – and you can tweak its specification to suit your needs. You can save money, too, particularly if you have a source of cheap scrap metal.
The second type of machine requires the jaws to be mounted on arms that pivot on bearings or bushes. The size and accuracy of the required holes will be a challenge if you only have hand tools at your disposal. For this reason, we’re going to make the first type. However, we’ll give the jaw more travel so it can accommodate undulating workpieces like the second. We’ll only be making one frame, so the jaws will need to be capable of being rapidly swapped from shrinking to stretching.