What is axial clearance?
By Zoe Moser
What is axial clearance? What should we watch out for? And what possibilities does igus offer for reducing axial clearance?
The question of clearance is often asked when dealing with lead screw nuts made of polymer. Clearance describes the lost motion, i.e. the “dead travel” on the lead screw, or in other words the gap between the thread flanks of the lead screw and the lead screw nut. In this context, the correct technical term is axial clearance. This term describes the movement of the lead screw nut in an axial direction while the lead screw remains stationary.
Lead screw systems require a minimum clearance in order to function properly. If the axial clearance is too small, the torque required to move the lead screw nut will also increase.
Considerations for your lead screw system
In addition to the axial clearance caused by manufacturing tolerances, application-specific influences must also be taken into account. In addition to thermal and hygroscopic environmental influences, the minimum clearance to be considered in the application must also take into account the friction heat generated by the application. This factor plays a decisive role in connection with the expansion of the polymer material used. Essentially, the axial clearance in the system can change with temperature fluctuations.
How can I reduce the axial clearance?
To reduce unwanted clearance, the correct choice of materials is important. Pretension mechanisms have also proven to be effective for clearance reduction. For our dryspin® high helix threads and trapezoidal threads, there are three versions with pretension: Zero-Backlash, Low-Clearance and AB lead screw nut.
For applications with high loads, high temperatures or in heavily polluted environments, a standard lead screw nut should always be used. The reason for this is that in these situations, a reduction of clearance by using a pretensioned lead nut can cause issues with friction and performance.
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