When the factory cable guide broke, I called Rube Goldberg for some design help. He stopped by and this is what resulted:
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The disign is loosely based on Paco's design, using 0.98 High Density Polyethylene. The 8-inch width was choosen to help eliminate electrical noise from the spindle. So far, it works great. The alpha hasn't stuttered once from electrical interference since I made the change.
The aluminum is the 1010 size from 80/20. A similar guide runs along the x-axis, but it is constructed from 3/4-inch black pipe.