Model of gear hobbing machine

This model conforms in general outline, though not in actual scale of certain parts, to the gear hobbing machines manufactured by Henry Wallwork & Co Ltd Manchester.

It is capable of generating spur gears, worm wheels, spiral gears, etc, up to the limit of its capacity for holding blanks.

The machine uses a hob with the teeth formed with straight sides, and set at an angle to the axis of the hob corresponding to the pressure angles of the gears to be generated.

The form of tooth generated is involute, which curve is formed by the combination of the motion of the tooth of the hob, and the rotation of the blank upon which teeth are being generated. In cutting spur gears the helix angle of the hob is brought parallel to the teeth of the spur wheel by setting the cutter head, which can be set to any angle from 0 0 to 1 80 0 by one-minute intervals. When worm wheels are to be generated the axis of the hob is set to the angle at which the worm will mesh with the wheel.

The hob is set for spiral gears so that the helix angle of the hob corresponds with the helix angle of the spiral gears to be cut. Sets of change wheels provide the various ratios for cutting different numbers of teeth and for various feeds. Both feed and counting gears must be calculated to work together in a definite ratio when spiral gears are cut.