Re: [CAD_CAM_EDM_DRO] Re: Max feedrate

andrewyslee wrote:

>Hi,
>
>What are the factors that determine the max. feedrate?
>

The short answer here is that Max feedrate is limited by your mechanical
design ( motors, drivers, gear ratio's etc.), provided that you are not
"Using up" all of the step capability of the program. Some designs will
run faster, some much slower.

> The max.
>steps/sec that can be output by the computer or the driver (max.
>volt, amp. etc.)?
>

This can consist of a few things. First and foremost, it helps to know
what the particular programs capabilities are. Most current versions of
what is available and discussed on this list comes near or around
25,000-30,000 steps per second ( someone may know what some of the
available programs really are). You can contact the Developer of your
program to find out the "possible" step output, keeping in mind that an
older Processor could have an effect on your possible output.

One must realize that depending on your driver settings, and actual
distance traveled per 200 motor steps via your drive mechanism, you
might need to divide that step "availability" properly across your
multiple axis.

I'm working on a clear comment.............

Ok, Say you have 5000 steps per second to "appropriate" to a particular
axis.

If you were driving motors at "full" step, one step per pulse, you'd
(in theory) get your motor to move 5000 "Motor Steps" (1.8 degree - 200
steps) PER Second.
In reality, your motor may not be able to run that fast, especially with
a load applied.

Now, on the other side of the coin, If you had your drivers set to "10"
stepping, like a Gecko, you would immediately divide that 5000 steps by
10, dropping your capability to only 500 Motor steps per second.

As you can see, those 10 microsteps can burn up a whole lot of
capability, especially across 3 or more axis.

Lead screws have a similar effect. If you have a screw that moves .500",
compared to .100" per turn, you will use only 1/5 of the "Available
steps" with the .500" screw. Whether your motors can "pull" the larger
screw is another question.

So, machine design has a lot to do with things as well. One should
consider what is "necessary" in your design, and build around those
needs. I am pretty convinced that I would have a hard time watching a
machine like a Sherline conduct rapids at 30ipm or so ( someone tell me
what they do hit ).... I think I would bolt the thing down, and shoot
for 100ipm with larger motors and Faster screws. You could certainly get
close, if your target resolution was kept in the neighborhood of .0005,
instead of what they must be getting with those fine screws and 10
microstep drivers.

Chris L