Converts continuous rotary motion of pinion into reciprocating rotary motion of C Gear. Derived from the book "507 Mechanical Movements" Video at http://youtu.be/DzJzle83oas Printed in ABS with .2mm layer height. Print one of each. Depending on your printer's calibration, you may or may not have to glue a few of the mating pieces together. If parts to stay pressed together, glue the square end of the "C Gear Shaft" into the "C Gear". Glue the smaller OD of the "Pinion Shaft" into the ID of the "Pinion". Slide the "Pinion" thru the slot in the "Frame" and glue the "Crank" on to the square drive. The "Pinion" has a unique up-and-down motion while turning the "C Gear", and the "C Gear" will reciprocate back and forth. Spin and enjoy!!