Origin: Believe it or not, this is said to have come from a blacksmith forum..
This is one I typed a a while ago, so I get to re-use it!
How to make a Flexible Template:
Before you start, you need to go to a sign shop, and buy a roll or two of 1" and 2" wide "Release Tape". Its a low tack tape that sign guys use to put vinyl letters on with. Then stop and pick up some nylon strapping tape at a stationary store.
1.) Clean the panel that needs to be reproduced.
2.) If panel is bad, fix with Bondo , or bang out to shape as best as you can. The more accurate the shape, the more accurate your reproduction will be.
YOU CAN USE THE SHAPE FROM THE OTHER SIDE IF ITS 100% OPPOSITE.
Meaning, if the left side is a mirror image of the right side, USE THAT.
3.) Apply Release tape at a 45* angle on the panel, with edges meeting, but no overlap if possible.
4.) Apply Nylon strapping tape 90* to the Release paper, with minimal overlap.
Carefully remove both layers of tape. Apply some talcum powder, bondo dust, whatever, to the release papers adhesive. You now have a template of the shape you are trying to reproduce, showing ALL of the shape.
IF YOU WANT TO REUSE THE PATTERN , do not use the talcum. Apply another layer of tape on the INSIDE of the pattern, and cut the ragged tape edges. Apply a nylon tape border around the perimiter.
OK, now drop the pattern on a flat sheet of sheetmetal. The loose areas indicate where the metal will need to be stretched. And the tight areas need to be shrank. As you pound (stretch) the metal, it fits the flexible template more and more. You will need to learn how to "tuck shrink" in order to save yourself a ton of time, as well. (See Metalmeet.com ) This is where the baseball bat comes in handy. The bat is cut so that you are using the very end of the bat (striking end), and the handle of the bat becomes the handle of the mallett. The yard sale bat is a CHEAP way of making a durable mallet with enough depth to accomodate most projects. The leather shot bag, or convex tree stump gives the metal a place to go. The shot bag can be something as simple as a plain purse filled with washed sand (avoid silicosis).
You don't have to spend tons of cash. Just be creative, and pay attention to the way the metal moves.
Now you have a lumpy piece of metal thats close to your pattern. You have 3 choices. E-Wheel, plannishing hammer or Slapper and dolly. The first 2 are self explainitory.
Using a slapper is nothing more than having a dolly to support the metal, and striking the raised portions of the metal to flatten it out, being careful to not alter the shape of the metal you are creating. As the bumps go down, adjust your force. Basically, you are using the slapper like a wide hammer.