Gear Hobbing Machine

Overview

A gear hobbing machine cuts spur and helical gears by generation, not by copying a tooth shape. A worm-shaped cutter, the hob, and the gear blank both rotate, and the machine holds their rotations in an exact ratio, turn the hob once and the blank advances by one tooth pitch. As the meshing hob teeth sweep through the blank they roll out a true involute profile, the same way two gears mesh. One hob therefore cuts every gear of a given module and pressure angle, whatever the tooth count, which is why hobbing is the volume method for automotive and industrial gears.

The machine stands on a rigid Bed & Column. The blank fixtures onto the Work Spindle & Table, a rotary table driven through a worm reduction so it turns slowly and stiffly. Above it the Hob Head & Arbor spins the hob on a both-ends-supported arbor and swivels to the gear's helix angle. Three feed slides position the cut: the Radial Slide (X) sets tooth depth, the Axial Slide (Z) runs the hob down the full face width, and the Tangential Slide (Y) shifts the hob along its length to even out wear.

How it works

The heart of the machine is timing. On older machines a train of change gears and a differential mechanically tied the hob to the table; here the Electronic Gearbox does it electronically, reading both the Hob Spindle Motor and the table encoders and commanding the Table Rotary Drive to hold the ratio to within arc-seconds. Lose that synchronisation and the teeth come out malformed, so the loop runs in hard real time.

The operator enters the gear data, module, tooth count, helix angle, face width, at the CNC Control, which computes the ratio, the swivel angle and the feeds. The Coolant System floods the contact with cutting oil to clear chips and heat. The hob spins up, the radial slide feeds to depth, and the axial slide carries the hob down the blank; as it travels, the Motion Controller keeps every axis locked together so the teeth generate cleanly from top to bottom of the gear.