LEXICONMachine components
Drive sprocket
Also called: Final drive sprocket, driving wheel
The toothed wheel at the rear of a tracked undercarriage that converts hydraulic motor torque into track movement by engaging the bushings of the track chain.
What it does
The sprocket is the only powered contact with the track. Its teeth engage the bushings between the links, so the tooth profile is designed around bushing diameter and chain pitch rather than around another gear. It is bolted to the final drive, a planetary reduction unit driven by a hydraulic motor, and it takes the full torque of the machine in both directions. Tooth counts are usually low — often under twenty-five — because the reduction has already happened upstream.
Why it becomes an object
Sprocket teeth wear into hooked asymmetric profiles, and the direction of the hook records whether the machine spent its life travelling forwards or reversing. Because engagement is with a bushing rather than a mating gear, wear is heaviest on one flank, which makes the asymmetry pronounced and readable. Sprockets are replaced on tooth profile alone, so the hub and web arrive structurally intact, and the resulting form is a dense radial star with an obvious centre.
