A worm gear set is the classic right-angle drive: one input revolution moves the wheel by exactly one tooth per worm start, which gives large reduction ratios in a single stage, quiet operation and an inherent self-locking tendency. But unlike a simple spur gear, a worm pair can only be cut when a full set of parameters is known. In practice, the most common gap in customer drawings is exactly this — the module and the number of starts are missing.
The parameters that define a worm set are few but non-negotiable: module, number of wheel teeth, number of worm starts, pressure angle, lead angle, hand of spiral and centre distance. Together they fix the tooth profile and the mounting position. If the drawing shows the wheel outside diameter and the tooth count, the module can be estimated from the standard formula (outside diameter ≈ module × (teeth + 2)), but the starts of the worm and the centre distance must still be confirmed before a set can be quoted or cut.
Material pairing is where a worm set earns its reputation. The wheel is usually cut from phosphor bronze (PB-2), tin bronze or high-strength brass, because bronze has low friction against steel and resists scuffing under sliding contact. The worm itself is made from alloy or case-hardening steel such as EN24 or 42CrMo, carburised and hardened to 50-55 HRC with a hard case depth of 1-2 mm, then ground. The hard, ground steel worm running against the soft bronze wheel is the standard combination for long service life.
The process chain reflects that pairing. The worm is turned or milled to the thread form, case-hardened, then finish-ground on a thread grinder to hold the flank profile, lead accuracy and surface finish. The wheel is hobbed with a worm-type hob or milled with a fly cutter, then finished by precision turning of the bore and faces. After cutting, the pair is matched for backlash and contact pattern, which matters more for worm sets than for ordinary gears.
Reverse engineering keeps many worm sets alive. When the original drawing is lost or the old pair is worn, a supplier can measure the module, starts, lead angle, centre distance and hand of spiral from the worn parts, confirm the pairing with the customer, and produce a set that drops straight into the existing housing. This is the fastest path for spare parts and localised replacements.
At our factory, worm shafts and worm wheels are machined in-house, including thread grinding after case hardening. Send us your worm set drawing — or the old pair for measurement — together with quantity and target delivery, and we will confirm the parameters and send a quotation within 24 hours.