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General Mach Discussion / Re: Backlash comp help
« on: September 01, 2010, 12:13:18 AM »
Dave, there is an easy way to measure backlash directly that you might like to try. Using the same setup that you described, move into the indicator 0.25 in or so, (approx. mid-stroke). Now set BOTH the DRO and the indicator to ZERO. Continue in the SAME direction for another 0.1 or 0.15 in, (just a bit more than the expected backlash). Now reverse direction and step back to the DRO zero. Now read the backlash directly from the indicator. As a check continue movement for a little more than the backlash and then step back to the DRO zero. The indicator will (should) read zero. This should repeat precisely all day long, (for that location of the lead screw). If not then as others have suggested, there is definitely some other problem in addition to backlash.
Note that the backlash probably will not be consistent throughout the length of the lead screw. It is usually greater in the center (due to the most wear) than at the ends. You will want to take that into account when you do set your backlash comp.
Another thing that is troublesome is that you commanded a .007 move but only got .0066 movement. That is unrelated to backlash since there was no reverse movement involved. It would imply that it is a calib (steps/in) error, but that is too short an interval to draw that conclusion. But the bottom line is that the DRO and indicator should agree. Possibly another clue to a mechanical problem? Have you checked your calib over a longer distance?
Al
Note that the backlash probably will not be consistent throughout the length of the lead screw. It is usually greater in the center (due to the most wear) than at the ends. You will want to take that into account when you do set your backlash comp.
Another thing that is troublesome is that you commanded a .007 move but only got .0066 movement. That is unrelated to backlash since there was no reverse movement involved. It would imply that it is a calib (steps/in) error, but that is too short an interval to draw that conclusion. But the bottom line is that the DRO and indicator should agree. Possibly another clue to a mechanical problem? Have you checked your calib over a longer distance?
Al