The threaded member of a worm drive, which meshes with a worm wheel on a non-intersecting shaft at 90 degrees. Each turn of a single-start worm advances the wheel one tooth, giving reductions from about 5:1 up to 100:1 in a single stage. Motion is almost entirely sliding, so efficiency falls as the ratio rises, and low-lead worms can be self-locking, though not reliably enough to replace a brake.
Single-start worm on the gate operator, so forty to one in one stage, and it won't back-drive unless something shakes it.
Never count on a worm drive to hold a load; vibration and wear can let a so-called self-locking set back-drive.
Also heard as
- worm screw
Related terms
Worm wheel
The gear driven by a worm, with throated teeth that wrap around the worm, usually made of bronze.
Gear ratio
The number of teeth on the driven gear divided by those on the driver, setting speed reduction and torque gain.
Scuffing
Sudden adhesive damage where tooth surfaces weld and tear apart because the oil film broke down.