Belted Reduction Gear for Nema 17

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**update 22/05: Added reduction_plate_60t.stl file for pulleys with up to 60 teeth**
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This reduction box supports reductions of up to 2: 1 or 1: 2
I'm creating another one for reductions of up to 3: 1 but that will unfortunately be a little larger to accommodate the larger pulley.

This reduction box can also be used to increase the speed of a lead screw. In this case you should use the larger pulley in the engine and the smaller one attached to the lead screw. This is useful