How are CogChamp gears made?
Cogchamp primarily uses hobbing to cut gear teeth.
Hobbing is a process that can use one tool to cut virtually any spur or helical gear within the same module and pressure angle. The cutting teeth on a hobbing tool simulate the shape of a straight-tooth gear rack. As it cuts the teeth of the gear, this straight-tooth shape translates and rotates, forming a perfect involute tooth profile in the gear.
Hobbing is also the primary method for cutting wormwheel gears, although the unchanging diameter of the hobbing tool makes it less configurable for wormwheels of different worm diameters.
Limitations of hobbing:
Hobbing requires clearance on both faces of the gear, which means this method cannot be used to cut herringbone gears or stacked compound gears. Trying to do so would gouge the tooth surfaces of one or both gears in the stackup. If the advantages of a stacked gear are absolutely necessary, here are some ideas to get around the limitation:
- Make each gear as a separate part, then attach them to the same shaft. This won't work if angular alignment is critical (such as for some stacked planets and herringbones), as CogChamp can't guarantee tooth clocking (not yet anyways - see below)
- Try spacing the gears apart to give enough clearance for the hobbing tool to enter and exit the cut:
Hobbing cannot be used to cut internal gears or bevel gears. Since the hobbing tool simulates a rack gear, it can only be used to cut gears that can interface with a rack gear (in the case of a wormwheel, the worm is effectively a rack gear).
Hobbing cannot guarantee “tooth clocking”, or the angular positioning of any tooth relative to some other eccentric feature. While our automation guarantees that all features made by the same hobbing tool and same setup will be in the same place, this is not maintained after the hobbing tool is replaced or serviced. In short, don't depend on hobbed gears to give a consistent angular alignment of the teeth to other features.
CogChamp is always looking to expand our capabilities, and we plan in the near future to include:
- Single Tooth Gearcutters - for accurate tooth-clocking and pseudo-bevel gears
- Expansion of hobs into wormwheels
- Single-point cutters for worm gears
- Shapers and/or skivving tools for internal gears and reduced-clearance compound gears