The hydraulic actuator is responsible for clamping the work piece. Hydraulic fluid from the Hydraulic Power Unit (HPU) applies pressure to a piston within the actuator.  The piston then moves fore or aft, clamping or unclamping the work piece. The drawtube is threaded onto the actuator’s piston and then onto  the chuck or collet.  When the piston actuates, the drawtube moves with it, and this is what transfers the clamping and unclamping motion of hydraulic actuator to the chuck.

Common issues with a hydraulic actuator include vibration and leaking. Vibration can be mitigated by ensuring that all of the spindle drivetrain components have the least amount of geometric misalignment possible.  Leaking can be caused by worn seals within the actuator. These can be replaced with a kit from the actuator's manufacturer.

1. Hydraulic Actuator (i.e. Union, Cylinder)
2. Drawtube
3. Chuck
4. Hydralic Power Unit (HPU)

If the hydraulic actuator is leaking it can appear to be dripping out the coolant collector or between the static and rotary body of the actuator.  This can be caused by an obstruction in the return line or worn seals.  Make sure all hydraulic hoses are free of kinks and tight bends to allow for free flow of hydraulic fluid. If you suspect the seals are worn, order the appropriate seal replacement kit for per the actuator model number.  

If you are seeing a loss of clamp force or cavitation noise coming from the HPU, then the hydraulic fluid may have become contaminated with coolant.  Check the following:

• Coolant dripping onto the HPU [1]
  • If the coolant collector is filling up and spilling out the cover then make sure the drain line is free of debris [2]
  • Spindle liners could be transferring coolant rapidly to the coolant collector when using two liners for smaller work pieces
    • Place rubber gaskets between liners to prevent coolant from leaking out [3]
• Check the chuck o-ring seal for wear and tear and replace if necessary.  Apply grease each time it is installed. If the chuck o-ring is worn coolant could enter between the drawtube and spindle bore, allowing coolant to transfer to the unions seals
• Troubleshoot the HPU for faulty solenoids or low oil per the Hydraulic Power Unit Troubleshooting Guide

If you are troubleshooting a vibration issue and you suspect that the hydraulic actuator could be the cause, do the following before replacing any components.

• Check radial runout of the actuator on the steel strip [2] not to exceed (NTE) 0.0005" (0.0127 mm)
  • If there is excessive runout then remove the hydraulic actuator and drawtube assembly. 
  • Reset the runout on any mated components of the spindle drive.  Depending on the machine frame size this could be the spindle shaft, spindle pulley, spindle adapter [1], and hydraulic actuator [2], [3]. See Section 2 of the Lathe Spindle Troubleshooting Guide for more information
• Check the radial runout of the drawtube [5] on inner diameter NTE 0.010" (0.254 mm)
  • If the runout of the actuator is within tolerance but the drawtube is not, then remove the drawtube and reinstall
• Balance the spindle - See Section 3 of the Lathe Spindle Troubleshooting Guide