A Gear Cut by the Fellows Cutter: 40 Teeth Generated, Not Drawn

In Fellows's machine the blank "is rotated step by step in unison with the cutter" while the cutter reciprocates across it, and each stroke planes away a little metal. His specification lists the result: "The cutter generates the form of the curve of each gear-tooth cut on the blank, so that each tooth cut is theoretically correct," and "One size of cutter for any given pitch will cut any size of gear." This model was made the same way. The 24-tooth cutter was rolled one full turn around a 105 mm blank in 2,400 positions, and each position was subtracted from the blank.

Lay it flat on one face. It needs no supports. PLA is fine for a display model. Two copies at 100 mm centres have no tip clearance and no backlash, which leaves no room for printing tolerance, so a printed pair is for studying the tooth form.