Helical gears vs spur gears

When comparing spur gears and helical gears, it is widely accepted that spur gears are noisier than helical gears. This difference in noise levels stems from the way the planets, sun gears and internal gear engage with one another. 

Each of the 2 solutions has pros and cons.

Spur Gears Are noisier than helical gears

Spur gears, with their straight teeth, generate acoustic waves as they mesh. This is due to the "contact ratio" – the number of teeth engaged at any given time. In spur gears, the contact ratio typically falls below 2.0, which is the threshold where gears tend to run quietly.

When fewer teeth are in contact, the system generates more noise.

Helical gears generate axial loads on internal components

Having a helix angle allows more teeth to be in contact simultaneously. This increases the contact ratio, often surpassing the 2.0 threshold, which results in a quieter operation.

However helical gears generate axial forces that can apply stress on internal components such as bearings and friction disks. If these loads are not managed properly, they can reduce the lifespan of the planetary gearbox.

Helical vs spur output pinion?

A helical pinion meshing on a rack or another gear will generate axial loads on the gearbox shaft.

We consequetly recommend using:

• helical pinions and racks with helical planetary gearboxes, as opposite axial forces will reduce the loads on the bearings,
• spur pinions and racks when the gearbox has straight teeth internal gears (like our Access, Spirit, or Init series).