Re: [CAD_CAM_EDM_DRO] stepper motor accuracy

> From: <ccs@...>
> > However, I wouldn't worry about it on a machine tool, and here's why.
> > To get decent torque and small increments, you are going to use
> > substantial gear and screw reduction. For example, 1:4 reduction
> > driving a 5 tpi screw. That's effectively 20 tpi or .050 per
> > revolution. Dividing into 400 half steps gives increments of .000125.
> > That's the best you can hope for in terms of positioning, so this is
> > clearly not a high precision machine
>
> Aiming for such accuracy is all very laudable but, in real terms, is it
> really achievable on a 'home' machine? Does anyone here actually measure
> their parts to 1/10th thou or better and do they worry if they're off by one
> or two?

Maybe, maybe not. My point was that if your machine has 8000 half
steps to an inch you have a fighting chance or doing good work. If it
has 2000 or even 1000 half steps per inch, you have no chance - a half step
of deflection will throw you way off.

Generally, the machine needs to work in smaller increments than the
tightest tolerance you want to hold.

I will mention that I've put a dial indicator on an 8000
half-step-inch lathe and gotten nice results. But then that is what
one would expect as stepper motors are fairly accurate and most screws
are good over a short distance as long as you don't reverse the feed.

Predictability of the cut diamter I think depends mostly on the
stiffness and alignment of the iron.

Chris Stratton