Re: [CAD_CAM_EDM_DRO] Elastic belt stretch, lead screw twist, and far end encoders

"Heuver, Brad (B.R.)" wrote:

> I finally got around to doing the math on the differences between
> timing belt stretch, and shaft twist.

<snip>

> From this whole math lesson we learned the following:
> With the CNC described above, the belt stretch causes an error of 0.0065",
> and the screw twist 0.0001" or simply put, the belt error is 65 times the
> size of the lead screw twist, and ball screws are not frictionless so
> therefore, the belt stretch, being upstream of the friction, will be even
> greater than this.

Thanks much for doing this exercise! Very useful info. It does look like
it is important to put the encoder on the leadscrew, not the motor, as I
suspected. (Of course, there are other sources of error in addition to
stretch, too.) I'm surprised at how little twist there is on the screw.

Jon