A hobbing machine uses a cutting tool to make gears, sprockets, and splines. It uses a pair of mandrels to mount the hob and workpiece, with the ratio of rotational speeds determining the number of teeth. Hobs are classified by the largest gear they can produce, and can be vertical or horizontal. They have spirally arranged cutting teeth with flutes to remove chips, and may have one, two, or three wires.
A hobbing machine is a machine that produces gears, as well as similar parts such as sprockets and splines. It uses a cutting tool, or hob, to make teeth into the workpiece in a series of progressive cuts. This process is accurate and relatively inexpensive, making it the most common method of cutting gears. A hobbing machine is suitable for making gears in a wide range of quantities and styles.
A pair of mandrels is used with a hobbing machine. The hob is mounted on one spindle and the workpiece is mounted on the other spindle. The angle between these spindles depends on the specific type of gear the gear hobbing machine is making. The hob then rotates the shafts of the two spindles, which causes the hob to begin cutting the work piece.
The ratio of rotational speeds between the two spindles determines the number of teeth the hob cuts into the workpiece. The number of teeth the gear will have is equal to the number of threads in the hob multiplied by the gear ratio. For example, if a hob with two flutes rotates 10 times faster than the workpiece, the hob will cut 20 teeth in the workpiece. A large workpiece may already have rough cuts before it is mounted on the hobber. This allows the gear hobber to make final cuts more easily.
Hobbing gears are classified by the largest gear they can produce. For example, a hobber that can make a gear with a pitch diameter of 12 inches (30.5 cm) is known as a 12-inch (30.5 cm) hobber. A modern gear maker might be able to produce gears up to 10 feet (3.05 meters) in diameter. Hobs have drive motors and larger hobs typically have a tailstock and spindle.
A vertical hob mounts the workpiece vertically and a horizontal hob mounts the workpiece horizontally. Vertical hobs are generally the most common, although horizontal hobs are more useful for longer pieces. For example, a spline at the end of a shaft will likely require a horizontal gear.
The hob for a hobbing machine is cylindrical with spirally arranged cutting teeth. These teeth contain flutes that help cut the work piece and remove chips from the work piece. Hobs typically have one wire, although they might have two or three wires. Multi-threaded hobs are faster but less accurate.
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