Re: [CAD_CAM_EDM_DRO] Linux EMC step rates & Compaq EN SFF

> I'm giving serious consideration to using EMC to upgrade a Denford Triac CNC
> training vertical mill. Can anyone give me a guide as to what are the
> limitations on step rate output via parallel port. I'm planning to use Gecko
> stepper drivers with step /direction input - probably micro stepping.
>
> Am I limited by the data rate via the parallel port itself, or the processor
> speed - can anyone put some numbers around this so I know what the limits
> are.

The computer can generate step pulses extremely quickly. The problem
is that the ratio between the fastest step rate and the 2nd fastest is
2 to 1. Near their top speeds, steppers need to be accelerated very
smoothly. So you have to use a step rate much lower than the timing
interval to get reasonable increments of rate.

An 8000 step/inch setup works on a 200 mhz pentium, but the user
interface bogs down a lot when it is trying to run the realtime loop
fast enough to get much feedrate with this many steps. Best to get a
400 or 600 mhz processor for a stepper system, and consider using the
multiplying gecko's to keep the step increment reasonable (ie, don't
make it smaller than .0001 inches)

> As a secondary question, has anyone got EMC running from the BDI on a Compaq
> EN small form factor (so I know it likes it before I buy one!), as this
> machine just nicely slips into the original housing of the mill electronics.

Some may give you a specific answer - it would help to know the
processor and motherboard chipset used. You could also check on that
computer's compatibility with the linux version used in the current BDI.

Chris