No need to use c-clamps or Vise grips any more on your metal brake. Inserting material is now very easy.
Step 1: The Knobs
You will need to make or buy two knobs with 3/8 threaded posts like these. You will also need to open coil springs as shown here. The spring Inside diameter must fit over the 3/8 thread. I made the knobs 1 3/4" in diameter with the 3/8 thread protruding 3/4" inch out.
Step 2: Drilling the Holes.
Locate the upper clamp bar as if you were going to bend some metal. Make sure it is located correctly and oriented properly or your holes will be in the wrong place. Use a 5/16 drill to drill through the top bar and the bottom of the brake. Do this at both ends. Try to stay near the centre and about the same distance from the ends of the brake. It doesn't have to be perfect but will work better if you do.
Step 3: Tapping and Clearance.
Tap the base of the brake with a 3/8 - 16 tap at both ends. Re-drill the 5/16 holes in the clamp bar with a 25/64 drill so that the 3/8 knob screws will pass through them.
Step 4: Assembly
Place the open coil springs on top of the tapped holes then place the clamp bar holes over the top of the springs. Insert the knob screws through the clamp bar holes and springs and screw the knobs into the threaded base holes. Leave the knobs a little loose so that the sheet metal will slide underneath.
You are now ready to try it out just slide the sheet metal in and tighten the knobs and you are ready to bend.
You can view a You Tube video at :