Worm gearing
Gear selection
Thermal duty
How a worm gear reducer works
A worm gear reducer slows a motor and raises its torque in one compact box. This note follows the Pellam WG-90 from the motor flange to the output shaft, one part at a time.
Pellam Application Engineering12 March 20263 min readTechnical note PEL-TN-0412_BRevised 04/2026
Stock photo, for illustration.
In this note
A motor turns fast, and a conveyor, mixer or hoist needs to turn slowly with force. A gear reducer sits between them and trades speed for torque. The Pellam WG Concept is a worm gear reducer.
The worm and the worm wheel
The input shaft carries a screw-shaped gear called the worm. It meshes with a toothed disc, the worm wheel, and each turn of the worm moves the wheel on by one tooth. The two shafts sit at right angles, so the drive turns a corner as it slows down. Here the worm is hardened steel and the wheel is bronze. A hard worm against a softer wheel is a common pairing, because the wheel takes the wear.
What a 20:1 ratio means
The ratio is the number of teeth on the wheel divided by the number of starts on the worm. A single-start worm driving a 20-tooth wheel gives 20:1. The worm turns 20 times for one turn of the wheel.
| Input speed | 1,450 rpm |
| Ratio | 20 : 1 |
| Output speed, 1,450 / 20 | 72.5 rpm |
Torque rises in proportion, less some losses. With no losses, 2.2 kW at 1,450 rpm would give 290 N·m at the output. The WG-90 lists 210 N·m. The difference is lost to friction, and it turns into heat.
Where the forces go
A worm pushes sideways along its own axis as it drives the wheel. Bearings on the worm shaft take that thrust, and bearings on the output shaft carry the load on the wheel. In the cutaway you can see the bearings sitting in the cast housing. A cover plate closes the housing, and its bolts come out to reach the output bearing.
Heat and duty
Worm teeth slide against each other instead of rolling. That sliding costs more power in friction than a gear train whose teeth roll, and the lost power turns into heat in the housing. When you choose a size, check the heat the housing can shed against the work it will do, as well as the torque it has to carry. A reducer that is big enough for the load can still be too small for the duty.
Getting power in and out
The motor bolts to the input flange, which holds it in line with the worm shaft. The output shaft has a keyway, a slot that locks a coupling or a pulley to the shaft. The mounting details for the WG-90 are on the dimension drawing attached to this hotspot.
Other sizes and ratios
The WG series covers other sizes and ratios of the same design. A different ratio changes the number of wheel teeth. A different size changes the distance between the two shafts. A catalog page would list each one beside the WG-90.
Type designation
WG–90–20–B3–M
How a Pellam gear reducer code is read.
| Code | Meaning |
|---|---|
| WG | Series: worm gear reducer, cast housing |
| 90 | Center distance between the shafts, in mm |
| 20 | Ratio, 20:1 |
| B3 | Mounting position: foot mounted, shafts horizontal (B3) |
| M | Input: motor flange (M), free shaft (S) |
Data, WG-90
PEL-DS-9020_C, 03/2026.
| Series and size | WG-90, 90 mm center distance |
|---|---|
| Ratio | 20:1 |
| Input | 2.2 kW at 1,450 rpm |
| Output torque | 210 N·m |
| Materials | Hardened steel worm, bronze worm wheel, cast housing |
| Mass | 24 kg |
Concept product. Fictional specifications.
Terms
Worm
The screw-shaped gear on the input shaft.
Worm wheel
The toothed disc the worm drives.
Keyway
A slot that locks a coupling or pulley to a shaft.
Figures in this note
| Ratio | 20 : 1 |
| Input speed | 1,450 rpm |
| Output speed | 72.5 rpm |
| Output torque | 210 N·m |
| Center distance | 90 mm |
Documents
| Data sheet WG-90 (PDF) | PEL-DS-9020_C |
| Dimension drawing | PEL-DW-9020_A |
Technical Notes
Pellam Getriebe, concept company
Winterthur, Switzerland
Technical Notes
- All notes
- Worm gearing
- Gear selection
- Thermal duty
Downloads
- Data sheet WG-90 (PDF) PEL-DS-9020_C
- Dimension drawing PEL-DW-9020_A
Concept brand. Fictional company, demo for DITTO by Grey State Development.
Model: Warm Gearbox by T-FLEX CAD ST (Free), licensed under CC BY 4.0. No changes.