Zero Return Procedure for CNC Vertical Turning and Milling Machine
A proper zero return procedure is essential for ensuring the accuracy, safety, and repeatability of a CNC vertical turning and milling machine. In this context, this Zero Return Guide clearly outlines the correct steps to return machine axes to their reference positions. Furthermore, it discusses common faults and offers key parameter setup advice. By mastering this operation, machinists can not only prevent critical errors but also significantly improve operational efficiency.
1. Initial Power-On Checks
Before initiating zero return, verify that each axis (X, Y, Z) is moved sufficiently in the negative direction—typically 50mm or more away from the origin. Switch the mode to ‘Zero Return’ or ‘ZRN’ to prepare the machine for accurate positioning.
2. Axis Zeroing Steps
• X-axis: Press and hold the ‘+X’ button until the axis zero light indicates completion.
• Y-axis: Repeat with the ‘+Y’ button.
• Z-axis: Do the same with ‘+Z’.
After each axis returns, verify using the POS screen that coordinates read zero.
3. Troubleshooting Common Zero Return Problems
• No Signal Triggered: Check the proximity switch or mechanical stop for debris or misalignment.
• Wiring Failure: Measure line continuity and resistance; values over 1Ω may indicate a problem.
• Incorrect Reference Point: Modify grid offset parameter or physically adjust the stop block.
• Over-travel Alarm: Confirm axis start position and reassign work offset G55 if necessary.
• PLC Input Malfunction: Consider swapping the input channel or reprogramming the PLC logic.
4. Parameter Settings (FANUC & Siemens)
FANUC:
• Direction: Set via parameter 1006#5
• Grid Offset: Parameter 1850 = 1000 × screw pitch (e.g., 6mm = 6000)
• Use REF=1 for incremental encoders
Siemens:
• Parameter 34000 = 0
• 34060 = 2 × encoder grid interval
• 34200 = 3 if using distance-coded encoder
5. Operator Best Practices
• Always zero return before the first machining cycle of the day
• Inspect and clean zero point switches weekly
• Run dry cycles after ZRN to confirm axis alignment
• Press emergency stop (E-stop) immediately if unexpected motion occurs