Tormach PCNC 770 - How to Measure Lost Motion

Chapter 9
163
UM10350_PCNC770_Manual_0916A
Maintenance
Backlash: the major component of lost moon in a machine tool axis. It results from the clearance
between moving mechanisms. This is somemes referred to as play. There are two sources of
convenonal backlash that can be adjusted on the PCNC:
• Space between gib and way needed to support an oil lm. This is tuned by ghtening 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.
9.3.2.1 How to Measure Lost Motion
Correctly measuring lost moon is crical to successfully undertaking any of advanced maintenance
procedures detailed in the following secons. Mill setup and tuning is done under no-load condions.
The precision measurements recorded in the Tormach Cercate of Inspecon are taken under
no-load condions. The accuracy of a machined feature is not an indicator of machine precision.
Tool ex, workpiece ex, xture ex, thermal expansion, and other factors contribute to the overall
machined-part accuracy.
The following tools are essenal:
• Dial indicator
• Dial test indicator
• Magnec dial stand
The following method describes the proper procedure to measure X-axis backlash. An analogous
procedure is used to measure Y- and Z-axis backlash.
1. Mount a dial indicator to the mill table along the X-axis to the le of the spindle, with the p
poinng at the spindle.
NOTE: If your indicator only reads in increments of .001”, then the best you can hope for a reading is +/- .0005”.
For best results, use an indicator that has increments less than .001”.
2. Jog the Y- and Z-axis to posion
the spindle head so the indictor p
contacts the outer diameter of the
spindle cartridge (see Figure 9.1).
3. Carefully jog the X-axis in the
posive direcon unl the indictor
contacts the spindle. Aer inial
contact, connue to jog the X-axis
in the posive direcon so that the
dial makes at least one complete
revoluon; stop when dial reads 0.
4. Zero the X DRO eld in PathPilot
®
.
Figure 9.1