Re: Why is the push to such high step rates (Grex and Arc100)?

Regarding the positional accuracy of CNC machines and similar machine
tools, the greatest level of accuracy I have seen doesn't come from
high-resolution rotary encoders or steppers or servos. It seems as
though the high accuracy machines utilize a linear scale for feedback
as opposed to the conventional methods (encoder on motor).

Using a linear scale attached to the axis removes all the variables
between postion command and mechanical movement. You will notice that
on all CMMs they use linear scales for feedback and on the newer
machine tools with linear servos they also use linear scales. Even on
conventionaly driven CNC machine tools, there is usually a builder
option to increase accuracy through the incorporation of linear scales
in the feedback loop.

But, reality is reality too. You cannot expect to hold .0001"
tolerances with a machine tool that isn't designed specifically for
that as well as a machining processes that is suitable for the task.
So, while you might see a claim of .000004 resolution by a machine
builder, don't expect to actually achieve that in your typical machine
shop.

Chris