This invention relates to a hobbing machine of the type in which a hob on a rotatable hob spindle is rotated in precisely timed relation with a gear blank on a rotatable work spindle in order to form gear teeth around the periphery of the gear blank. Under very specialized circumstances, the axis of the hob spindle may extend perpendicular to the axis of the work spindle. In most instances, however, the hob spindle is inclined relative to the work spindle at a predetermined setting angle which is other than a right angle. The setting angle is determined as a function of the thread angle of the particular hob being used and, in cases where a helical gear is being formed, the setting angle is also a function of the helix angle of the gear.
In virtually every hobbing machine, it is necessary to be able to adjust the center-to-center distance between the axis of the hob spindle and the axis of the work spindle while maintaining the same setting angle. Adjustment of the center distance is necessary, for example, to enable a gear blank to be loaded onto or unloaded from the work spindle, to enable the depth of cut of the hob into the work to be established and/or to enable the hob to be brought into proper working relationship with the work after the hob has been re-sharpened and reduced in diameter.
Most hobbing machines which presently are in commercial use are so-called universal hobbing machines. That is, the hobbing machine is adapted to be used with several different hobs and is adapted to be changed over to enable the formation of many different types and sizes of gears. While a universal hobbing machine is extremely versatile, that very versatility causes the overall construction of the machine to be both complex and expensive. Most universal machines include adjustable hob and work slides, an adjustable hob swivel and other adjustable components and also include a complex drive train with several sets of change gears for driving the hob and work spindles in various timed relationships. The complexity and expense of a universal machine are of little value to a gear manufacturer who wishes to make only a single type of gear or a very narrow range of gears. Moreover, the various adjustment capabilities which are present in a universal machine tend to introduce a lack of stiffness and precision into the drives for the spindles, several disadvantages resulting therefrom.