This thing is a printable ratcheting pulley block, designed for 550lb Paracord (other 1/8 inch or ~3.0 mm rope will likely work too, but I have only tried paracord). It allows you to easily raise and lower a hanging object. To see exactly what this thing does, please watch this short video...
The Paracord Ratchet works for me right off the print bed without any clean-up. I have been printing these in PLA with 20% infill and three extra shells on all layers. All the stress at the holes is radial to the axles, so I figured it's best to have a few layers around each hole for reinforcement. I also recommend printing the solid sides of the housing 100% filled, in Skeinforge 41 (which I am still using :P) I do this by setting the solid surface thickness layers to 4. With a layer height of .28 mm, this guarantees the 2.0 mm sides will print solid while other sections will have 20% fill.
Note: The file RatchetSolidWorks.zip contains the SolidWorks files for all five parts.
Assemble using 4-40 x 1.0 inch bolts (x5) with 4-40 lock nuts (x5) or M3 x 25 mm bolts (x5) with M3 lock nuts (x5). If you don't have lock nuts, you can use jam nuts (two regular nuts locked together). The lock nuts are necessary for proper functionality, the wheel axle and release pivot nuts need to be slightly loose so they don't pinch the housing and restrict component rotation. They should be tightened so they just barely touch the housing. Regular nuts will spin off the bolts when the ratchet is in use. Lock-tite or super-glue can also be used also to secure standard nuts in the proper position. The three bolts that hold the housing together should be fully tightened.
A spring or rubber-band is also necessary for this thing to work properly. I picked up a few small extension springs from the local hardware store, the one in the pictures is about 9.0 mm long (coil end to end, not including the hanging loops) and about 6.0 mm in diameter. See the photos for one possible rubber-band configuration option. There only needs to be light tension, so just about any spring or rubber-band that fits will work.
HOW TO USE:
To use this thing, first attach one end of your paracord to your secure hanging point. Then thread the other end down through the opening on the top of the Paracord Ratchet, and down the side of the wheel where the housing is open. While holding the release lever down (not necessary but it makes it easier), turn the wheel and paracord together until the paracord travels around the wheels and comes out the top again. It may be necessary to use needle nose pliers or something to guide the end of the cord out. Once the end of the cord is coming back out the top, it is ready to use. See the video link above for a short demonstration of the Paracord Ratchet in use.
IMPORTANT: Test your ratchet to make sure it operates properly before hanging anything from it!