A small amount of axial play in a stepper motor shaft is generally normal. Most stepper motors are designed with a certain degree of axial clearance, and a wave spring washer is typically installed behind the rear bearing to absorb cumulative manufacturing tolerances. However, excessive play may indicate a mechanical fault. Use the following troubleshooting steps to identify the cause.
1. Power-Off Manual Check
Disconnect the motor from any load (e.g., remove the timing belt or coupling). Rotate the motor shaft by hand while gently pushing and pulling it along the axial direction. Pay attention to the following:
- Does it rotate smoothly? If you feel any roughness or binding, the bearings may be damaged.
- How much axial play is present? If the clearance is small (typically less than 0.3 mm for most standard models) and has a springy feel, it is likely due to the normal wave spring washer preload. Refer to your motor's datasheet for the specified axial play tolerance. If the clearance is large and feels loose, it may indicate a problem with the internal bearings or positioning components.
2. No-Load Running Test
Run the motor with no mechanical load connected. Power it on and operate it at various speeds. Observe whether the axial play persists.
- If the play disappears under no load: The issue is most likely caused by the external mechanical installation or coupling.
- If the play persists under no load: The problem lies within the motor itself (e.g., a bearing issue or structural defect).
3. Check Operating Conditions
In applications that involve pressing, thrust, or similar axial loads, additional axial support (e.g., thrust bearings or external mechanical stops) may be required to prevent excessive axial loading on the motor shaft. Without proper support, the wave spring washer can become over-compressed and permanently lose its elasticity. This increases axial play and may cause noise during high-speed operation.
Conclusion
Excessive axial force on the shaft can permanently deform the wave spring washer, resulting in increased axial play over time. Every stepper motor has a specified axial load capacity that must not be exceeded.
Axial play is a standard design feature in most stepper motors; the wave spring washer behind the rear bearing serves to accommodate manufacturing tolerances. If your application cannot tolerate any axial play, consider selecting a solution that incorporates an external locking or preloading mechanism.