The structural part of the Z-axis in my RepStrap 3D printer is a pair of 8 mm rods which were fixed only at the base of the printer. When printing a higher speeds, both X and Y-axes are causing the Z-axis to wobble a bit. This has not been a problem so far, but especially when printing tall objects, there where some unwanted artifacts. I decided to make the Z-axis stronger in a weekend when all the shops where closed and I had to use the materials I had at hand. The top of the Z-axis was connected to the corners of the base of the printer using steel wire which was once used to hold up a curtain.
I printed 2 plastic pieces with an 8 mm hole in the bottom to fit at the top of the vertical rods. I used 123d to design the part.
The steel cable was fastened using the metal pieces I removed from a terminal block like this:
The pieces from the terminal block where used both a the top of the printer and below the base of the printer.
Adjusting the tension of the wires is not very easy in this setup, it requires 4 hands. But once set up, I expect this to last for a long time. This printer is stronger now and the printing quality improved again a bit.