Service Home How To Procedures C-Axis - Engagement Offset - Lathe - ST-15-35 - NGC
Last updated: 05/13/2025

C-Axis - Engagement Offset - Lathe - ST-15-35 - NGC

Revision A - 05/2025

C- Axis Engagement Offset - ST-15-35 - Lathe - NGC

The NGC Lathe C-axis, no longer uses tool change offsets for orienting the C-axis relative to the Spindle.  When the C-axis is commanded to engage, it commands the C-axis to its Zero position and commands the Spindle to the Spindle Orientation position (which is established during the alignment process)

How to Set C-Axis Engagement Offset - Video

C-Axis Disc Runout Check/Adjust

1

Make sure the C-axis is disengaged (M155), and the spindle can turn freely.

Verify that the runout of the hydraulic union is less than 0.001" TIR.

If it is not, loosen the bolts that hold the C-axis disc just enough so that the runout of the disc and union can be adjusted with a soft mallet.  Verify that the runout of the hydraulic union is less than 0.001" TIR.

2

Once the runout of the union is within specification, set the runout of the C-axis disc.

Place a small drill bit across the C-axis disc teeth for the indicator to land on. This prevents the indicator from interfering with the gear teeth.

Set the drill bit at four spots around the entire diameter of the disc to measure the runout. If the runout is greater than 0.001" TIR, tap the C-axis disc with a soft mallet to bring it within specification.

Torque the C-axis disc bolts after the runout of the union and disc are within specification.

Set C-axis Engagement Offset

1

Break the C-axis mount bolts loose but keep them slightly snug [1].

Move the mount away from the disc by turning the adjustment screw to the right (tightening on a normal bolt) [2].

2

Insert the Service USB key and go into Service Mode.

Go to the Settings tab

  • Set 216 Servo And Hydraulic Shutoff to 5000 sec.

Go to the Parameters > Factory tab 

  • Set 4.082 SPINDLE ORIENT OFFSET or 30.085 Spindle Orient Offset (SI Units) to 0
  • Set 7.078 C_AXIS TOOL CHANGE OFFSET to 0
  • Set 7.140 C_AXIS GRID OFFSET to 0
  • Set 7.019 C_AXIS INVIS AXIS to FALSE. This makes the C-axis visible.
  • Set 7.326 C_AXIS ENABLE SELECTIVE POWER SAVING to Disabled. This enables the C-axis to hold position when engaging the C-axis gear. The parameter will reset to its default value after Cycle Powering the machine.

Note: Make sure the C-axis is NOT engaged and the gear teeth will not touch.

Orient the Spindle:

  • Press [Current Commands] go to Devices Tab
  • Navigate to Main Spindle Orient
  • Press [F2]

Zero Return the C-Axis:

  • Press [Zero Return] 
  • Press [C]
  • Press [Single]

3

Press [RESET] but do not move the spindle or C-axis gears more than a tooth.

Note: The [RESET] button is used instead of E-stop so that the C-axis stays oriented.

Mesh the gears by turning the adjuster screw to the left until the C-axis drive gear is fully engaged with the disc gear. The mount may need to be pushed in by hand or tapped with a soft mallet to make sure the gears are fully meshed. The screw will start to stick out when fully engaged. See Red Arrow.

Note: Check that the drive gear is not engaged on the top of the disc gears tooth.

Slightly snug the mounting bolts.

4

With the C-axis gears fully engaged, set the Spindle Orient Offset:

  • Press [DIAGNOSTIC] and go to Parameters Tab, then Factory Tab
  • Enter 4.082 or 30.085 and [F1]
  • Press [S+F3]Press [Y]

5

Now that the spindle offset is set, back the C-axis off using the adjustment screw. Fully disengage the gears, and move them apart until they can not touch. Don't move the spindle to check, just watch the gears. 

Engage the C-axis in [MDI] using command M154. 

The C-axis gears must mesh fully and smoothly. Use an inspection mirror to see the gears and verify the engagement.

If the teeth do not mesh, restart the procedure.

6

Ensure the 4 bolts are just barely snug. Adjust the adjustment screw until the gears are almost fully engaged. You should still be able to feel some backlash between the gears.

Place an indicator on one of the teeth of the C-axis gear. 

Warning: Do not jog the C-axis without first removing the indicator.

Adjust the adjustment screw, while gently moving the gear back and forth by hand, until the backlash is between .002" to .003".

Remove the indicator and hand jog to 90, 180, and 270 degrees, checking the backlash at each point.

Go to the spot with the least amount of backlash, this should be the high spot.

Continue adjusting the backlash here until it is between .0003 to .0005" at the high spot. Torque the 4 cylinder block bolts and verify that the backlash is still within range.

Remove the indicator and disengage the C-Axis by pressing the [E-Stop] and [RESET].

7

Press [RESET] and engage the C-axis by pressing [C], then [HANDLE JOG].

Note: Do not move the C-axis.

With the C-axis at 0 and the gears fully engaged, set the Spindle Orient Offset again.

  • Press [DIAGNOSTIC] and go to Parameters Tab, then Factory Tab
  • Enter 4.082 or 30.085 and [F1]
  • Press [S+F3]Press [Y]

8

Press [E-Stop] and [RESET]. 

Orient the Spindle by pressing [Current Commands] and go to the Devices Tab. Navigate to Main Spindle Orient and press [F2].

Press [HANDLE JOG] then [DIAGNOSTIC] and navigate to the Axis Tab and to the spindle column.

Note the Actual Position value.

Press [RESET] and press C in the Jog Keys area to engage the C-axis.

Note the new Actual Position value.

If the new Actual Position value is greater than +/-0.035. Redo the C-axis engagement until the value is within spec.

9

Go to the Settings tab

  • Set 216 Servo And Hydraulic Shutoff to 120 sec.

Run the C-axis test program to verify the C-axis engagement is correct.

Download the program here.

Listen for smooth operation and no gear noises during engagement. If any faults occur, restart the procedure.