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

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