The machining of gears involute is actually carried out by by using hobs or rack-cutter, on their own proper machine, usually followed by grinding.

Altough for small modeles hobbing technology for machining involute surface before grinding is probably the best one, for large modules hobbing takes a lot of problems, since both the machine tool and tools become very expensive and very little flexible.

Then it is necessary to handle a very heavy and delicate tooly, while machine table is required to turn at high speed without any precision loss.

Gear machining by milling may be a good answer to such problems, with machining time very interesting and a lot of further advantages.

For low-quality gears milling might be used as the final involute machining.

In the following chapters we'll show that gear milling is geometrically correct, technically executable and economically convenient, and that for large modules the hobbing technology is obsolete, although the only apparent technical evolution of hobs and hobbing machines.