I needed a small clamp to hold printed circuit boards during milling on my home built CNC machine. Screw-type clamps would have to be used upside down and interfere with the head, while spring-type (or clothespin-like) clamps exterted either too much or too little pressure and were prone to bending my PCBs a bit, even on a backer board.

Then I found AndyGadget's elegant bungee-based vise on Instructables:http://www.instructables.com/id/Quick-Clamp-Release-Vice-Vise/ and realized I could use his design ideas to build a bungee-based clamp.

The clamp has four pieces. The main body and lower jaw are required. Retaining clip prevents the lower jaw from falling out of the groove and handle makes for an easier grip on a bungee. Retainer clip is a tight fit into the holes, I used pliers to squeeze it in.

I used a 4mm bungee that holds tent poles together. I also glued pieces of neoprene on each jaw for a better grip.

Depending on your print quality, you might need to clean up the lower jaw insert, so it slides easily in the groove. A drop of lubricant also helps.

The main STL file, bungee_clamp.stl prints all four pieces. There is also a separate STL file for each piece.

I am including the openSCAD source file for the clamp, as well as the filleted_cuboid.scad library file - it should be accessible to your openSCAD as plib/filleted_cuboid.scad. It's part of my openSCAD primitives library (https://www.thingiverse.com/thing:1679551) and is used to make each jaw.

I put no restrictions on this design and related code. You are welcome to use, share or modify it as you see fit.