Editing Computer numerical control (section)

==Numerical precision and equipment backlash==
Within the numerical systems of CNC programming, the code generator can assume that the controlled mechanism is always perfectly accurate, or that precision tolerances are identical for all cutting or movement directions. While the common use of [[Ball screw|ball screws]] on most modern NC machines eliminates the vast majority of backlash, it still must be taken into account. CNC tools with a large amount of mechanical [[backlash (engineering)|backlash]] can still be highly precise if the drive or cutting mechanism is only driven to apply cutting force from one direction, and all driving systems are pressed tightly together in that one cutting direction. However, a CNC device with high backlash and a dull cutting tool can lead to cutter chatter and possible workpiece gouging. The backlash also affects the precision of some operations involving axis movement reversals during cutting, such as the milling of a circle, where axis motion is sinusoidal. However, this can be compensated for if the amount of backlash is precisely known by linear encoders or manual measurement.

The high backlash mechanism itself is not necessarily relied on to be repeatedly precise for the cutting process, but some other reference object or precision surface may be used to zero the mechanism, by tightly applying pressure against the reference and setting that as the zero references for all following CNC-encoded motions. This is similar to the manual machine tool method of clamping a [[Micrometer (device)|micrometer]] onto a reference beam and adjusting the [[Vernier scale|Vernier]] dial to zero using that object as the reference.{{citation needed|date=November 2017}}