Re: So many choices - Best way to make Sherline CNC

Message: 20
Date: Mon, 19 Nov 2001 05:42:41 -0000
From: mszollar@...
Subject: So many choices - Best way to make Sherline CNC

I'm know that this has been asked over and over again but cannot find
one with this twist. There are basically (as I understand it) 2
options to convert a Sherline Mill to CNC. 1 would be to use stepper
motors, and another (?) to use servo motors. My question is which is
better and more accurate? In my browsing I noticed that the servo
kits (e.g., G320) and motors use feedback, this verifies position,
move, etc. I've seen/heard of stepper motors that have encoders on
them but haven't seen a driver that supports feedback directly
(unless I'm missing something). So my question holds; what is the
best for the $ if you want accuracy (is feedback really
required/best)? Oh, consider that I've noticed that Camtronics is
out of 5A driver (if that would have been the way to go).

Thanks,
Ken

[Steppers equipped with encoders seem to work more like servos (which are
basically encoder-equipped DC motors). The feedback loop does help maintain
accuracy and compensates for lost steps, which can otherwise be rather
disastrous for your part. I've heard that EMC will close the loop on
encoder-steppers, but haven't tried it myself. If you're looking for a
ready-to-run solution (once you solve some mounting issues) consider the
MaxNC CL motion-control kits. They have a 3-axis single-stack kit for $875
that includes the encoder/stepper motors, software, and control box, but not
the limit/home switch kit ($60 extra). The single-stack motors are probably
adequate for anything you want to do on the Sherline, but they also have a
double-stack kit for slightly more that puts out more speed and torque. One
advantage of this system is that one can add a fourth axis without having to
add a parallel port or another control box. ]

Andrew Werby
www.computersculpture.com
Discount Pricing on Scanning, Modeling and CNC Systems