Re: What is the weak link in machine precision - Knee Mills

John,

My thoughts apparently bleed into each other while writing. Yes, I
understand the specs are describing the parallelism and squarness.
What I ment to say is that I would not pull it apart and install ball
screws right away. Live with the acme nut and take out the slop with
the backlash compensation in the software. Yes, I agree it will grow
with use.

Thanks for the input on the servos. I need to do some more looking
around and find parts and prices.

Tom.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> zipdrive2k wrote:
>
> >Peter,
> >
> >Thanks much for the help and I will let you know what I find out
as
> >far as machines. Enco has a mill they state the specs are
> >0.00078/ft. error for squarness and parallelism. If it is
> >that 'good', I might not even pull it part for installation of
ball
> >screws and just use the backlash compensation in the software.
> >The 'only' bad thing about the machine is that it does not have
> >chromed ways.
> >
> This has nothing to do with backlash. All they are telling you is
the
> errors in axis orthogonality will not exceed .00078" per foot of
motion.
> That is not bad for a basic mill. Your backlash, however, is going
to
> be WAY more than that. Most likely, it will be somewhere in the
> neighborhood of .010", and will grow over time.
>
> >
> >Have you ever measured the load (current) on any of the motors
during
> >max acelleration? I would be very interested to see how little /
> >much the motors are being used. I would like to run steppers and
I
> >am wondering if a 1000 in-oz. or 1250 in-oz. would be large enough.
> >
> >
> Current in stepper motors may not have a lot to do with
acceleration.
> Generally,
> the current is maximum at zero or low speed, and decreases as the
motors
> run faster, as the available power supply voltage can't reverse the
current
> fast enough due to winding inductance. This is the bane of stepper
systems,
> and why servos can outperform them.
>
> Jon