Re: Digest Number 350

ARMILITE@... wrote:

> From: ARMILITE@...
>
> Hello All:
> First, I am no machinist or techy. But I have an interest in home
> hobby
> shop machining and CNC. I use a Mac mostly, but I have an old IBM 486
> 100
> MHz, 36 Meg Ram, 8x CD, 8 Gig HD laying in my gun room collecting
> dust. Now I
> can't seem to find much info in the way of CNC for the Mac other than
> Virtual
> Gibbs, an AuraCad/Cam, even though there is a lot of Mac CAD programs
> for it.
> So I have resigned myself to digging out the old 486 and brushing the
> dust
> off it. Also I have a Grizzly 12 x 37 lathe, and their large Bench
> mill/drill
> with power feed for equipement. I have a few dumb questions to ask of
> you
> people in the know.
>
> #1 Which is better, steppers or servo drives?

I prefer servos for several reasons. If you use DC tachometers, the
servo can
provide constant velocity even between servo updates from the CPU. You
do not have trouble from resonances in steppers. Accuracy is not
affected
by variations in the spacing of the stepper's steps. Servo motors are
capable
of delivering high peak torques, which are ideal for a machine tool
environment
for accelerating and decelerating the load. Finally, of course, servos
with
encoders will not lose position when bound up, e-stopped or under other
circumstances, like crashes.

> #2 What is the aproximate cost of each type of motor?

Medium size servo motors are often cheaper surplus than big steppers.

> #3 What size and brand of motors would you recomend for my size lathe
> and
> mill?

I'm using 1/8 Hp, 1725 RPM servo motors on the X and Y axes of my
Bridgeport.
A smaller motor does for the Z axis, and would also do for most lathes.

> #4 Do you have to buy a certain board to work with certain software or
> are
> they unversal?

In both cases, no, not universal. Stepper boards are probably more
easily converted
from one program to another.

> #5 Which board/software combos do you recomend?

I'm using EMC with the Servo-to-Go board, and am in "7th heaven" with
how well
it works!

#6 What kind of cost for the boards/software?

NIST makes EMC freely available, Linux is free for the downloading,
although the CD and book make installation easier unless you have a
VERY fast internet connection. The Servo-to-GO card I use is $888.
I made my own servo amps.

> #7 What companies offer catalogs for these kind of parts, motors,
> boards,
> ball screws, etc.

Herbach & Rademan (NJ) at www.herbach.com is a good one
Burden's Surplus Center, in Lincoln, NE is good for motors
C&H Sales in Pasadena, CA is expensive, but they have a great selection
of motors, etc.

> #8 Has anyone done this already in this group to my brand of machines?

I did a Bridgeport - see it at
http://www.artsci.wustl.edu/~jmelson/Machining.html
under CNC topics.

> #9 Lets say theoretically I may have access to a copy of MasterCam 7.2
> on CD,
> is all I need is the stepper/servo board to work with it, the
> stepper/servo motors and a ball screw for my mill?

I'm not familiar with MasterCam, but if it supports motion control,
it will likely be for steppers, only, as is the case with most other
one-piece CAM/CNC packages.

For servo systems, you need servo amps, either shaft encoders or linear
encoders, and usually a DC tachometer. Many servo amps require
an external power supply.

The only software I'm aware of that does the entire machine
control job is EMC. There are some other packages that run
multi-axis servo motor systems, but they generally do not have
all the functions to go straight from G-code to the servos, with
a user interface (control panel on screen).

Jon