Gear cutting
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Gear cutting is any number of methods used to manufacture precision gears.
Gear hobbingis a method by which a special hobbing cutter and gear blank are rotated at the same time to transfer the profile of the hob onto the gear blank.
Spur and other straight gears may be cut or ground on a milling machine/jig grinder utilizing a numbered gear cutter, and any indexing head or rotary table. The number of the gear cutter is determined by the tooth count of the gear to be cut. Any straight gear can be produced in this way.
To machine a helical gear or twist drill on a manual machine, a true indexing fixture must be used. Indexing fixtures can disengage the drive worm, and be attached via an external geartrain to the machine table's handle (like a power feed). It then operates similarly to a carrage on a lathe. As the table moves on the X axis, the fixture will rotate in a fixed ratio with the table. The indexing fixture itself receives it's name from the original purpose of the tool: moving the table in precise, fixed increments. If the indexing worm is not disengaged from the table, one can move the table in a highly controlled fashon via the indexing plate to produce linear movement of great precision (such as a vernier scale). An enterprising hobbyist who has need of many helical gears would be well served by a quick-change gearbox.
For very large gears or splines, a vertical broach is used. It consists of a vertical rail that carries a single tooth cutter formed to create the tooth shape. A rotary table and a Y axis are the customary axes available. Some machines will cut to a depth on the Y axis and index the rotary table automatically. The largest gears are produced on these machines.
The old method of gearcutting is mounting a gear blank in a shaper and using a tool shaped in the profile of the tooth to be cut. This method also works for cutting internal splines.
[edit] See also
- Hobbing machine
- Gear shaper
- Gear grinder
- Gear cutter
