the slippage occurs because the belts rollers are not parallel. you can possibly adjust the position of the pivots on one of the rollers. What tool you would use to create a datum i do not know. perhaps if you mounted two laser pointer tangently on one roller then you could measure the distance between the 2 points and the two pointers. Once those points are relatively the same distance apart then it should be aligned.
Ben
March 2011
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