What is a spur gear?
The teeth are cut parallel to the shaft, so a pair of spur gears must mesh on parallel axes. They are easy to make and carry no axial thrust, but all the teeth in contact engage at once, which makes them noisier at high speeds than helical gears. The size of the teeth is set by the module, and a standard pressure angle makes gears from different makers interchangeable when other data match.
Listed manufacturers
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List your companySpur Gear or helical gear?
Spur gears are simpler and cheaper and create no axial load, but they are noisier at speed. Helical gears run more smoothly and carry more load, but need bearings to take the axial thrust.
What to specify when you ask for a quote
- Module, number of teeth, pressure angle and face width.
- Material and heat treatment, such as case hardening, and the hardness.
- Quality grade and the standard used, which sets tooth accuracy.
- Bore, keyway or spline, and the hub dimensions.
- Backlash allowance and the centre distance with the mating gear.
- Surface finish and the inspection report for critical gears.
Where it is used
- Industrial MachineryGear trains, drives and machine tools.
- AutomotiveTransmission gears and starter drives.
- AgricultureFarm machine gearing.
Frequently asked questions
What is the module of a gear?
It is the ratio of the pitch diameter to the number of teeth, in millimetres, and it fixes the size of the teeth. Two gears must have the same module to mesh.
What is backlash?
It is the small clearance between meshing teeth. Some backlash is needed for lubrication and thermal expansion, but too much causes noise and positioning error.
How are gear teeth hardened?
Commonly by case hardening, which gives a hard surface and a tough core, or by induction hardening of the teeth. The process and hardness should be stated on the drawing.
How can I order a replacement gear?
Provide the drawing or a sample with the number of teeth, module, pressure angle, width, bore and material. The supplier can measure a sample if the drawing is lost.