Worm and Wheel Must Be Made Together
A worm drive gives a big speed reduction at a right angle in a single stage, and at low lead angles it's self-locking — the worm drives the wheel, but the wheel can't drive back. The catch is that the worm and the wheel are a matched pair: they must share the same module, lead, pressure angle and centre distance. Make one without the other and they won't mesh. We machine them as a set, classically a hardened steel worm running on a bronze wheel so the dissimilar metals run cool and wear slowly.
Custom Worm Gear Specifications
| Attribute | Capability |
|---|---|
| Set | Worm shaft + worm wheel, matched |
| Starts / ratio | Single or multi-start; high single-stage reduction |
| Worm material | Hardened steel (e.g. 4140) or stainless |
| Wheel material | Phosphor / aluminium bronze (plastic for light duty) |
| Self-locking | Advised on, depends on lead angle & friction |
| Bore & keyway | To shaft fit; keyway to DIN 6885 / ISO 773 |
Ratio, Lead Angle & Self-Locking — the Numbers That Matter
Two things trip people up on worm drives: how the ratio works, and whether it self-locks. Both come down to the worm's number of starts and its lead angle:
| Question | Rule |
|---|---|
| Reduction ratio | = wheel teeth ÷ worm starts (not teeth ÷ teeth) — e.g. a 40-tooth wheel on a single-start worm = 40:1 |
| Self-locking? | Yes when the lead angle ≲ 5° (strictly, lead angle ≤ friction angle) — the worm drives the wheel but the wheel can't back-drive |
| Single-start worm | Highest ratio & strongest self-locking, lower efficiency |
| Multi-start worm (2–4) | Higher efficiency & smoother, but lower ratio and usually not self-locking |
| Efficiency | Falls as lead angle drops — self-locking sets trade efficiency for holding power |
So if you need the drive to hold position without a brake (a lift, jack, damper or valve actuator), you want a low-lead-angle single-start set; if you need efficiency, a multi-start worm. Tell us the ratio you need and whether it must self-lock, and we'll design the starts and lead angle to suit.
How We Make / Reproduce a Worm Set
- From specs: ratio, centre distance and shaft sizes — we derive module, lead and tooth count.
- From a sample: we recover module, lead/lead angle, starts, tooth count, pressure angle and centre distance from your worn worm and wheel (see reverse engineering).
- Pair the materials: hardened steel worm + bronze wheel for low friction and long life.
Material Pairing
The classic worm-drive pairing is a hardened steel worm on a phosphor- or aluminium-bronze wheel — the dissimilar materials reduce friction and let the cheaper wheel wear in preference to the worm. For light duty a plastic wheel is possible. Mesh, bore and keyway are verified on inspection.
Worn worm or stripped wheel? Send both parts if you can — having the pair lets us confirm module, lead and centre distance precisely and machine a matched replacement set. No drawing required. See also our discontinued gear guide.
What Self-Locking Actually Costs You
Self-locking is not free, and the page above only says efficiency falls. Here is the size of the fall. A worm drive is self-locking precisely when its forward efficiency is below 50 % — that is the same statement as “lead angle below the friction angle”, just expressed in a number you can measure on a test rig. Everything you gain in holding you pay for in heat.
| Worm starts | Lead angle | Forward efficiency | Back-drives? | Where it belongs |
|---|---|---|---|---|
| 1 | 3–5° | 40–55 % | No (self-locking) | Hoists, jacks, valve actuators, anything that must hold with the power off |
| 2 | 8–10° | 65–75 % | Usually yes | General reduction where a brake exists elsewhere |
| 3 | 13–15° | 75–82 % | Yes | Continuous duty, heat is the limit |
| 4 | 17–20° | 82–88 % | Yes | Where efficiency matters more than ratio |
The caveat that belongs on every self-locking drive: self-locking is a static property. A drive that will not back-drive under a steady load can still creep down under vibration, because vibration momentarily breaks the friction that does the locking. A self-locking worm set is not a brake and should not be the only thing holding a suspended load. If the application needs a hold that is certified, the holding device belongs outside the gearbox.
Why You Cannot Just Buy “a Module 2 Worm Wheel”
This is the part most people discover after the wrong wheel arrives. A worm wheel is not cut with a standard gear cutter — it is generated by a hob that is a replica of the mating worm: same pitch diameter, same lead, same pressure angle, same thread form. That is why the wheel has a throated face that wraps the worm instead of a straight one.
The consequence is unforgiving. A wheel hobbed for a Ø30 mm worm will not mesh properly with a Ø25 mm worm even when both are module 2 and both have the right tooth count: the throat radius is wrong, contact drops to a line instead of a wrap, and the wheel wears out in weeks. Module and tooth count are not a sufficient specification for a worm wheel. The worm's pitch diameter is part of the spec, which is exactly why worm sets are supplied as matched pairs and why a broken wheel usually means both parts.
And if the drive in front of you is a chain rather than a worm, the same replace-the-pair logic applies to custom sprockets — tooth count, pitch and bore matched to the chain you already run.
Recovering the Whole Specification From What Is Left
Most sets that reach us arrive incomplete — a stripped wheel, a scored worm, and no drawing. The specification is still recoverable, because the housing holds the one dimension that cannot lie: the centre distance. Three measurements are enough.
| Measure this | How | What it fixes |
|---|---|---|
| Centre distance a | Between the two bearing bores in the housing, not between the worn parts | The one datum that survives wear — sets the whole size of the pair |
| Wheel tooth count z₂ | Count them, even on a stripped wheel | With the ratio, tells us the number of starts on the worm |
| Worm outside diameter | Over the thread crests, on an unworn section near the shoulder | Cross-checks the module that comes out of the arithmetic |
From those, the module falls out of m = 2a ÷ (q + z₂), where q is the worm's diameter quotient and sits between 8 and 12 on nearly all industrial sets. The result is then checked against the measured worm crest diameter, which should come to m × (q + 2). When the two agree, the set is defined and can be cut. When they do not, the worm is not the original one — which is itself worth knowing before you pay for a wheel to match it.
What this means for ordering: send the centre distance, the wheel tooth count and the worm crest diameter and we can quote without a drawing. Send both parts and we confirm lead and contact pattern directly instead of deriving them. Either way the pair is cut together and the contact is checked on assembly — see parts reproduced from a sample, obsolete and discontinued parts, or other gearbox parts. Bores and keyways to the fit you need, per ISO 286.
Material Pairing, With Designations
The worm is the hard part and the wheel is the sacrificial one, deliberately: bronze is cheaper to replace than a hardened shaft, and it embeds debris instead of grinding against it. In practice that means a worm in 42CrMo4 or 16MnCr5 hardened and ground, or 1.4301 where corrosion beats load, running against a wheel in CuSn12 phosphor bronze for general duty or CuAl10Ni5Fe4 aluminium bronze where the load is high and shock is present. Aluminium has no place in a worm wheel that carries torque — 6061 and 7075 are for the housing and the covers, not the mesh. Plastic wheels are real but belong under a few newton-metres, in instrument and actuator work.
Where the Catalogue Stops on a Worm Set
| What the job needs | In the catalogue? | What happens then |
|---|---|---|
| Standard ratio, standard centre distance, complete new set | Yes | Buy it from a gearbox supplier — a stock set is cheaper than anything cut to order, and quicker |
| Wheel only, to run against the worm you already have | No | Hobbed to your worm's pitch diameter and lead, because no stock wheel will mesh correctly |
| Centre distance fixed by an existing housing | No | Module derived from the housing, m = 2a / (q + z₂), then both parts cut to it |
| CuAl10Ni5Fe4 aluminium bronze wheel for shock loading | Rarely stocked | Cut from bar; CuSn12 remains the default for steady duty |
| Left-hand lead | No | Single-point cut, hand marked on the shaft so it cannot be fitted reversed |
| Gearbox brand no longer trading | No | Whole set recovered from the housing and the surviving part |
| One set only | Not as a special | One set is the normal order here — these exist because a machine is stopped |
The first row is meant literally: if your set is a standard ratio on a standard centre distance and both parts are being replaced anyway, a gearbox supplier is cheaper and faster than we are, and you do not need us for it. Everything below that first row is where the catalogue runs out.
What Moves the Price of a Cut-to-Order Worm Set
A worm set cut to order has no list price, because it is priced by work content rather than by the size of the gear. A 60 mm bronze wheel and a 160 mm bronze wheel can quote within a few percent of each other if the setup is the same. Five things actually move the number:
- Wheel only, or the matched pair. If your worm survived, only the wheel is cut and you pay for one setup. A new pair means two setups and a centre-distance check between them.
- Wheel material. CuSn12 tin bronze is the default and cuts easily. CuAl10Ni5Fe4 aluminium bronze takes shock loading far better and costs more, both as bar and in cutting time.
- Starts and lead. A single-start worm is the quick case. Multi-start worms (2–4) need a longer hobbing pass and tighter lead control.
- Hardening and grinding on the worm. A soft steel worm is fine for hand-operated and low-duty drives. Hardened and ground is a separate operation, priced as its own line so you can see what it costs before deciding.
- Quantity. The second identical set is far cheaper than the first, because the setup and the hob are already paid for. Every quote carries a ladder for 1, 5 and 10 sets so the break is visible.
Send the module, ratio, centre distance and material — or the worn parts — and the figure comes back within 12 hours. There is no tooling charge, which is why a single replacement wheel is a normal order here.
“Worm Gear for Sale” Usually Means a Reducer, Not a Gear
Most people searching for a worm gear to buy want a complete unit, and a complete unit is the one thing you should not have machined. A worm gearbox, a worm winch and a worm gearmotor are assemblies — housing, bearings, seals, shafts, often a motor — mass-produced at prices no machine shop can approach. What gets cut here is the gear pair inside them, which is what you need once the unit is obsolete or the housing is still good and the wheel has stripped.
| What you are looking for | Buy it or cut it? | The honest route |
|---|---|---|
| Worm gear reducer, winch or gearmotor — a complete drive unit | Buy the unit | Stock, every time. A mass-produced reducer beats a machined one on price and delivery, and we will say so rather than quote it |
| Standard ratio and centre distance, whole set being replaced | Buy the set | A gearbox supplier is cheaper and quicker — you do not need us for this |
| The wheel inside a unit that is still good — stripped teeth, housing fine | Not sold separately | Wheel hobbed to your surviving worm’s pitch diameter and lead |
| Internals for a discontinued gearbox — maker gone or no longer supplies parts | No longer available | Pair recovered from the worn parts and the housing centre distance |
| A ratio or centre distance the catalogue skips | No stock set will mesh | Starts and tooth count chosen to hit your ratio, then both parts cut to it |
Frequently Asked Questions
Yes — and it's the right way. The pair must share module, lead, pressure angle and centre distance, so we machine them together: typically a hardened steel worm on a bronze wheel.
Yes — we recover module, lead/lead angle, starts, tooth count, pressure angle and centre distance from the worn pair and machine a meshing set. No drawing needed.
At low lead angles the worm drives the wheel but the wheel can't back-drive — holding position without a brake. Whether a set self-locks depends on lead angle and friction; we can advise.
Hardened steel or stainless worm with a phosphor/aluminium-bronze wheel; plastic wheel for light duty.
There is no list price, because a cut-to-order set is priced by work content rather than by the diameter of the gear. Five things move the number: whether you need the wheel only or a matched pair (a pair is two setups instead of one), the wheel material (CuSn12 tin bronze is the default, CuAl10Ni5Fe4 aluminium bronze costs more and cuts slower), the number of starts on the worm, whether the worm is hardened and ground after cutting, and quantity — the second identical set is far cheaper than the first because the setup is already paid for. Send the module, ratio, centre distance and material, or the worn parts, and the quote comes back within 12 hours with a ladder for 1, 5 and 10 sets.
Nowhere off the shelf, and that is the whole difficulty with worm gearing. Gearbox suppliers stock complete sets at standard ratios and standard centre distances, and a stock set is cheaper and faster than anything cut to order — buy stock whenever your set is standard. The moment the centre distance is fixed by an existing housing, or your worm survived and only the wheel is gone, or the ratio you need is not on the chart, no stock part will mesh correctly and the gear has to be cut to your numbers. EKINSUN cuts worm and wheel to a measured worm or to a fixed centre distance, from 1 piece, quoted in 12 hours.
No, and you should buy those from stock rather than have them machined. A worm gear reducer, a worm winch and a worm gearmotor are complete assemblies with housing, bearings, seals and often a motor, mass-produced at prices a machine shop cannot approach. What we make is the gear pair inside them, which is what you need when the unit is obsolete, or when the housing and bearings are still good and the wheel has stripped its teeth. Send the worn wheel and the worm, or the housing centre distance, and the replacement pair is cut to fit the unit you already own.
The formulas are short enough to do on paper. Reduction ratio is wheel teeth divided by worm starts, so a 40-tooth wheel on a single-start worm gives 40:1 — not teeth divided by teeth, which is the usual mistake. Lead angle is the arctangent of (starts × module ÷ worm pitch diameter), and it is the figure that decides self-locking: at roughly 5° or below the wheel cannot back-drive the worm. Centre distance ties the pair together as half the sum of the two pitch diameters. Send those numbers, or the parts, and we check them against what can actually be hobbed before quoting.
Quote a Worm Gear Set
Worn pair, ratio or drawing — all accepted. Reply in 12h.
// Qty & price
1 pc
Sample price
Confirm fit before a run
10–50
Unit price drops
Setup cost shared
100+
Best price
All tiers quoted upfront
- →No distributor — you pay the maker directly
- →CAD saved after first order — reorder anytime at lower unit price