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Hobbing using a milling machine – introduction
Hobbing is a process whereby a cutter that has teeth in the form of a helix is turned against the workpiece. But, the speed at which the hob turns and the speed at which the workpiece turns have to be exactly right relative to each other.
On a traditional mechanical hobbing machine the linkage between the hob and the workpiece consist of all sorts of linkages such as telescopic joints etc and, of course, a gear train. All of this is specially organised for hobbing. Part of the problem is that as the hobbing proceeds the drive from one part to another can move in quite a complicated manner. This makes a mechanical linkage quite difficult to do on a milling machine.
The way round this is not to use mechanical linkages but to use electronic connections instead. For example, if the hob is being driven by the vertical spindle the speed at which this spindle rotates at is measured by using a shaft encoder fitted to the spindle. The output from this encoder is processed by a microprocessor. The output of the microprocessor is used to drive a stepper motor which, in turn, drives, for example, the dividing head.
There appear to be three types of gear that can be made by hobbing on a vertical milling machine.
a helical gear