Gear Manufacturing Using a Manual Milling Machine
The following article details how to machine a simple spur gear on a milling machine using a dividing head. A specifically shaped cutter must be used.
Making spur gears using a dividing head - This resource covers how to select a cutter, prepare the gear blank, and set up a dividing head on a horizontal or vertical milling machine. Is is critical that great care is taken at every step of the process to ensure the best results.
Gear Manufacturing in a Production Environment
Companies that specialize in gear production use processes like hobbing, shaping, skiving, and grinding.
Manufacturing Metal Gears
Gear Prototyping Methods
To manufacture just a few gears, a process that doesn't use specialized cutters or machines is a good choice. A wire EDM machine, which uses a very fine electrically charged wire to erode material, can be used to cut any gear with a straight tooth profile very accurately. Wire EDM machines are also very useful for other prototyping tasks and not only for gears. This article from Gear Technology describes how the machine works, what sort of tolerances are possible, and describes one company's method of making precise master gears with wire EDM.
A Sinker EDM can also be used to make gears with helical teeth, but this requires one or more custom electrodes.
Manufacturing Plastic Gears
Although plastic gears can also be cut using many of the same methods as metal gears, injection molding or extrusion is better suited to the mass production of gears from plastics.
As described in the page gear selection, plastic gears are often an excellent choice where many low cost, lightly loaded, gears are needed. Designing an mold for such a gear is quite a difficult process- as the part is cooled, it will shrink and change shape, especially if there are sharp corners, big changes in the cross section of the gear, or thick sections. This article from Stock Drive Products / Sterling Instruments explains many of these considerations. One big advantage is that many of the form and size issues with molded plastic gears are well tolerated by the softer material and the gears can often be used with minimal or no lubrication.