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Space between gib and way needed to support an oil film. This is tuned by tightening the gib.
The space between the ball bearings and races in the angular contact bearing pair that supports the ball screw. This is tuned by increasing the angular contact bearing pair preload.
Tools
Flat-bladed screwdriver
Dial Indicator (.0005” resolution)
Magnetic Base
Metric allen keys
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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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The “ADMIN GET_AXIS_BACKLASH” command will display the current amount of backlash for each axis. The “ADMIN RESET_AXIS_BACKLASH” command will reset the backlash values of all axes to 0.
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Note: There is no backlash compensation for the A axis.