Gear Shaving Machine

Overview

A gear shaving machine finishes the teeth of a soft, already-cut gear before it is hardened. It removes a very thin layer of metal from each tooth flank, a few hundredths of a millimetre, to correct the small errors left by hobbing and to put the right shape into the tooth. Shaving improves the tooth profile, the lead across the face, and the surface finish, and it can deliberately crown the teeth so the gear runs quietly and carries load evenly once it meshes. It is the high-volume finishing step for automotive transmission and axle gears, where millions of gears need the same accurate, quiet tooth.

The machine does not cut with a moving tool feeding to depth. Instead the Cutter Head carries a gear-shaped cutter that meshes with the work gear on the Work Head and drives it round. The two axes are crossed at a small angle by the Cutter Swivel, and that crossed angle makes the cutter slide lengthwise along the gear flanks as they mesh, which is the action that does the shaving. The Cross Feed Slide and Table Slide set the depth and run the cut across the face.

How shaving works

The Shaving Cutter looks like a helical gear, but each tooth flank is cut with many fine serrations, so the flank is a row of sharp edges. When the cutter meshes with the work gear and the axes are crossed, the mesh point slides along the flank, and those serration edges scrape off tiny chips. Because the cutter is the only driven member, the Cutter Spindle Drive turns the cutter and the cutter turns the gear; the Work Spindle runs free, held just loaded by the Spindle Brake so the teeth stay in firm contact. The crossed-axis sliding is set by the Swivel Table and locked by the Angle Clamp, because the angle controls how much sliding, and therefore how much shaving, happens.

Feed methods

The way the gear is moved relative to the cutter sets the shaving pattern. In conventional shaving the Table Slide traverses the gear parallel to its own axis past the cutter, and the Cross Feed Slide feeds in a little at each stroke end. Diagonal shaving traverses at an angle so the serrations sweep a different track, which improves finish and shortens the cycle. Plunge shaving uses a wide cutter and feeds straight in with no traverse, which is the fastest method for narrow gears. The CNC Control runs whichever cycle is programmed and lets the operator dial in profile and lead corrections, including the slight crown that makes the finished gear quiet.

Work and cutter heads

The Work Head holds the gear on a precise Work Arbor running in Angular Contact Bearing sets so it spins with almost no runout, since any runout would copy straight into the finished teeth. The Cutter Head carries the cutter on a stiff Cutter Arbor, also in angular bearings. Both heads sit on the Bed & Column, a ribbed grey-iron casting chosen to damp the fine vibration that would otherwise show up as chatter marks on the polished flanks.

Hydraulics, coolant and control

The Hydraulic System clamps the work arbor and applies the steady feed pressure that keeps the cutter loaded into the gear, supplied by the Hydraulic Pump and watched by a Pressure Sensor so the load stays consistent. The Coolant System floods the mesh with cutting oil through a Flood Nozzle to wash the very fine shavings clear, because trapped chips would mar the finish; the oil settles in the Coolant Tank before being pumped again. The CNC Control runs the crossed-axis feed from a CNC Controller, and the operator programs the part and corrections at the Operator Display.

Use and limits

Shaving is a soft finishing process: the gear is shaved before heat treatment, then hardened, and the small distortions of hardening are accounted for by shaving the teeth slightly off-shape so they come right after quenching. For gears that must be finished after hardening, gear honing or grinding is used instead because a shaving cutter cannot cut hardened steel. The shaving cutter itself is the costly part: it is ground to mirror the gear it finishes, so each gear design needs its own cutter, and the cutter is reground several times over its life as the serrations wear. A fresh cutter sets the tooth shape exactly, and as it wears the control trims the feed and corrections to hold the gear in tolerance until the cutter is resharpened. Shaving machines are a fixture of automotive gear lines for their speed and low cost per gear, with cycle times short enough to keep pace with a hobbing machine feeding them. Variants include rack-type shavers that use a straight toothed rack instead of a round cutter, plunge shavers built for narrow gears, and machines with automatic cutter measurement and wheel dressing for unattended running on a transfer line.