Re: Conversion Of Mill to CNC (LONG)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "camerashy44"
<camerashy44@y...> wrote:

> Although I have been monitoring this list for some time this is my
> first post. I am a complete novice at both milling and CNC so need

the

> help and advice of the very experienced and knowledgeable members of
> this list.

Wayne: I will jump on on just part of this. If you are not willing
to convert to ballscrews to get the accuracy from the mechanical
parts then servos are a waste of time and money. Steppers will place
the motor where it "thinks" the table should be. Using servos with
encoders the SHAFT of the motor will be exactly where it should be
but once again only within the tolerance of your leadscrew. You can
program in backlash correction in a lot of the Controller software so
you can factor some of it out (see www.artofcnc.ca).

The primary consideration of steppers vs servos is that servos
normally spin faster (RPM) and hold torque at high speeds better than
steppers. You can then trade speed for torque by gearing the drive
train down with stepped pulleys. All things being equal you can get
by with smaller servos than steppers and pickup the torque in the
gearing ratio.

Servos operate "closed loop" and have some tuning considerations but
with today's hardware closed loop designs (Gecko 320/340 series) its
pretty easy to setup. Servos will give you smoother moves but if you
use a good microstepping stepper driver then the moves approach a
servo type system. An important consideration for smoooth moves is
the ability of the controller software to do continuous contouring.

Your system will only be as accurate as the least accurate component
in the drive train.

There are a lot of guys that have been through the conversion
experience and can give you some good advice. A lot of our
experience has come from making mistakes and having to correct them:
the best kind of experience.

Whatever you do, stick with it. Nothing will equal the feeling you
will get when you are able to see your very own machine make that
first cut!