How much backlash does your application really require?

What is backlash exactly ?

- The backlash is not the precision of the gearbox. It is the result of the space left between the gears during assembly.

- A gearbox with the most precise gears can still have a high backlash if all components are not matched cautiously.

- To some extend, the opposite is true too : a poorly made gearbox can have a low backlash, if the internal gears are preloaded. Of course the backlash will vary depending on the angular position, the gearbox will be noisy, have a low efficiency and you can expect backlash to increase quickly.

- When all inner components are made perfectly and assembly is cautious, the gearbox is quiet, offers a low friction torque and low variations of backlash over a full turn.

1. The backlash is not the precision of the gearbox. It is a fragment of the lost motion which is only visible during reversals.

2. You may reduce the backlash by selecting precise output elements (ie racks and pinion) and taking the time to assemble them with the smallest backlash possible, as there is often more backlash between the pinion and the rack than in the gearbox.

3. Backlash is measured with 5% of the rated torque applied to the output shaft. When raising the torque, lost motion will increase more than the initial backlash value because you will start measuring stiffness – not only backlash. So, when looking for low lost motion, choosing a stiff gearbox is just as mportant as the backlash value.

4. A very low backlash (ie 1 arc-min in a Reckon planetary gearbox) is needed when you want to preserve the linear precision during reversals without measuring it with linear encoders and correcting it.

5. The lower the backlash, the lower the shocks during fast reversals. Backlash consequently has an impact on the lifespan of your entire system

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