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An Internal Ring Gear Cut by the Fellows Cutter: Teeth on the Inside
A 60-tooth internal ring gear whose teeth were made the way Edwin R. Fellows's gear-shaping machine (US 579,708, 1897) makes them. The same cutter that made the 40-tooth external gear was rolled inside a ring blank, and every position of the cutter was cut away.
Fellows counted this among his machine's advantages: one cutter cuts internal teeth as well as external ones. The flanks came out as true internal involutes. The tooth count, rim and face width are stated choices; the patent gives no dimensions.
Beginner
Several hours of printing; the slicer reports the exact time
Instructions
1
1
One cutter, inside and out
One cutter, inside and out
Fellows's specification: "The same cutter will cut either external or internal gear-teeth with equal ease and correctness. This is an important advantage, it being very difficult to cut internal gears correctly by any of the gear-cutting machines now in use." To make this model, the published 24-tooth cutter was rolled one full turn inside a ring blank in 3,600 positions, and each position was subtracted. Inside a ring, the cutter and the blank turn the same way.
2
2
The model in 3D
The model in 3D
Spin the ring in the viewer and look at the teeth on its inside. The cutter generated them, and no one drew them. It was built in FreeCAD and saved as one joined .blend mesh, editable in free Blender.
Tools needed:
Desktop Computer3
3
Print it
Print it
Lay it flat on one face. It needs no supports, but the bed must be at least 180 mm across. PLA is fine for a display model. Because of the interference stated above, it is not a working ring for the 40-tooth gear as drawn.
Materials for this step:
PLA Filament - Black (1.75mm, 1kg)1 kitTools needed:
3D PrinterMaterials
1- Placeholder
Tools Required
2- Placeholder
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