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Mount a dial indicator to the mill table along the X-axis to the left of the spindle, with the tip pointing at the spindle.
Jog the Y- and Z-axis to position the spindle head so the indictor tip contacts the outer diameter of the spindle cartridge (see Figure 9.1).
Carefully jog the X-axis in the positive direction until the indictor contacts the spindle. After initial contact, continue to jog the X-axis in the positive direction so that the dial makes at least one complete revolution; stop when dial reads 0.
Zero the X DRO field in PathPilot
In MDI field, program a positive X move of .01” at a feed rate of 5 IPM: G01 X.01 F5. The spindle head moves slightly in +X direction. When finished, indictor should read .010”.
Program an X move back to 0: G01 X0 F5. The spindle head moves slightly in the -X direction. The X DRO should say 0; however, the dial indicator should read a number very close to 0. This value is the measured lost motion.
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Loosen the upper gib screw eight rotations and tighten the lower gib screw eight rotations. This ensures that the gib clearance is quite loose.
Use a dial indicator to measure lost motion in the Z-axis (refer to How to Measure Lost Axis Motion earlier in this chapterTesting). With a very loose gib, the majority of the measured lost motion is attributable to the backlash in the angular contact bearing pair. On a new mill, this value measured should be less than 0.0015” on the Z-axis and less than .0013” on X- and Y-axis.
Tighten the gib by one turn by loosening the lower screw first, then tightening the upper screw. Measure the backlash again.
Repeat this procedure until the measured backlash begins to increase. At this point, the gib setting is slightly too tight.
Back the adjustment off to the point just before you saw the increased backlash. That is the ideal setting for the axis.
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