I’ve come up with a cheap and easy cable guide hack for use with RepRap 3D printers. The trick is to wrap the electrical wires in sleeving along with a piece of piano wire. I’ve used 0.8 mm piano wire, but anything between 0.5 mm and 1 mm will likely work fine.
The photo below shows a close-up of the wrapped electrical wires and piano wire powering the heated bed of my RepRap Prusa Mendel i2.
As you can see in the following photo, the piano wire keeps the cable arranged in a nice arc at all times, thus making sure it will never touch the heated bed or get in the way of its movement.
The top end of the cable harness is secured to the threaded rod using cable ties. The end near the heated bed is secured using a self adhesive cable tie mount as shown below.