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Revision 2 > http://www.thingiverse.com/thing:717447

A simple adaptation of the spring type belt tensioner into an adjustable and rigid form.

Fits GT-2 belts. OpenScad files included for your customization.

Print 1 part A, 1 part B to make a pair. For maximum strength, use concentric pattern, 100% infill in all layers.

Each pair requires :
1 M3x8 allen cap screw
1 M3 nut

Orient parts and install as shown in photos so the screw won't loosen as the belt is tensioned.
Place the tensioner as close to the carriage as posible.