RE: [CAD_CAM_EDM_DRO] Newbie questions

> What sort of size stepper motors will I need to drive the axes?
> As well as
> physical size, I'm interested in the power or current/phase.
> The A1S is a
> large mill (total weight of approx. 1/2 ton) but I won't be
> taking large or
> heavy cuts.

This question has a lot of variable to figure it out. First you need to have
an idea of the torque required to move the axis's. Then you need to figure
out the maximum rapid rate you want. Then look at the torque curve for the
motor as steppers drop off in torque very rapidly with speed. Then you have
to decide if your controller and software and the way you have the motor
hooked up will yield the same torque as the chart shows. I am sure there are
more considerations I am missing. For us hobby types we usually just guess
and see what it will do. There are some calculators on the web that help you
figure these things.

> What's the difference between a 4 wire and 6 wire (apart from 2 wires?)

4 wire is a bi-polar only motor. A 6 wire can be used either way (same with
an 8 wire).

> What resolution of control (in degrees?) do I need?

Normally you look at it from the standpoint of the table not the motor.
Meaning, you have to take into account the reduction of your drive system
(commonly cogged belts) and your lead screws. Then you figure out the actual
movement per step. Our egos will tell us we need ridiculously tiny moves per
step, but reality is .0001 - .0005" per step is probably good enough. Your
setup, technique, and tooling will probably have more of an influence on
your accuracy and precision at that point.

> What circuits do I need to drive these motors. I have seen information
> about driving steppers from the parallel port and "DANCAD?" software.

DanCAD is getting to be considered antiquated. The 2 most common programs at
the moment are CNCPro and EMC. CNC Pro is a commercial product from
www.YeagerAutomation.com and runs on DOS. EMC is a freeware product courtesy
of the US government and runs on Linux. It has a reputation as being
difficult to install (not necessary totally deserved, but definitely
different than setting up a DOS/Windows product). There is another program
called Master Control that is looking to be coming along quite well and runs
on Windows. There is a link from the FAQ list of links.

With any of these software packages you need stepper drivers. What you need
will depend upon the motors you end up requiring. If you want steppers you
can go with a 5 amp chopper driver kit from Camtronics (great supplier of
many of the parts and bits we use) or a complete micro-stepper driver from
Gecko. Another alternative are servo drives that you feed step and direction
signals. These are made by Geck. They have a lot of positive qualities, but
are a little more difficult to set up correctly compared to steppers (more
wires and some tuning required).

Hope that helps and feel free to keep asking questions to the list.

Tim
[Denver, CO]

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