Re: [CAD_CAM_EDM_DRO] re: Where does a newbe go to register?

Welcome aboard John,

I'll start out by saying, I'm no expert by any means but I do know
just enough too get me in trouble. If you can understand Basic,
Cobol, and Pascal you can understand this.

Start with the lathe, first off you will probably need to replace the
leadscrews with some ballscrews, or zero backlash leadscrews if
you have any slop in them at all. A few thousandths will probably
be ok at first, but you might want to start thinking ballscrews.
CNC software can handle some backlash, but too much
will produce poor results.

You will need to slap some motors onto those ballscrews to
make them go and you have 2 basic choices. Stepper motors
and servo motors. Stepper motors can be "stepped" by a
controller and your computer (hence the name, stepper motor).
Most stepper motors have 200 steps per revolution, so you can
have your computer tell the motor to move 2000 steps and you
just made 10 rotations of the motor. If you know how far the
leadscrew moves in one rotation, you do a little math and you
can figure how many steps it takes to move 1.45234 inches.
Of course the computer will handle the math part.
With the stepper motor you will require a stepper motor driver.
This is what converts the 2000 pulses from your computer to
a useable voltage and current to drive the motor. It also takes
a direction signal from the computer to drive the motor in the
proper direction. These are called "Step and Direction Drives"
Most stepper systems are open loop, send it the info to move
2000 steps and hope to god it does, because the software is
going to "assume" it did. There is no feedback on these stepper
systems. If it is designed well, a stepper system will work fine
for most hobby folks, and even some industrial systems.
For info on stepper motors see
http://www.cs.uiowa.edu/~jones/step/


Servo motors are used by most industrial and professional
machines. They too require a drive (servo drive) to generate
the required voltage and current to turn the motor, but they
also require some sort of feedback device, since a servo
does not have the 200 distinctive steps that a stepper has.
The feedback device is usually an encoder, which will generate
pulses as it moves. The computer counts those pulses and
"knows" how far the axis has moved. It then will figure where
the axis should be and output an analog signal that the drive
can understand. Usually +-10V. 0 Volts and the motor does
not move, +10V and it goes full speed in one direction and
-10V is full speed in the other direction. 5V = 1/2 speed etc.
The drive takes this analog voltage and converts it to the
proper voltage and current that the motor needs. Servo
systems are probably far superior than stepper systems but
usually cost more and are harder to set up. There is also
more software for stepper systems than servo systems in
the hobby price range.

CNC Software is what reads your part program and sends
the position info to the drives (stepper or servo). You can
download some of the free/shareware programs mentioned
on this list. Since most are for stepper motors which doesn't
require any feedback, it will work just fine without anything
attached.

G-Code is what the CNC software reads as your part program.
example of a very simple G-Code program

G0X0Y0Z1 'G0 is fast move to X,Y,Z axis positions
G1Z-.2F10 'G1 is move at set feedrate Z axis went down to -.2"
X10 'Move X axis to 10"
Y10 'Move Y axis to 10'
X0 'Move X axis to 0"
Y0 'Move Y axis to 0"
Z1 'Move Z axis up to 1"

This will cut a square on a milling machine -.2" deep. and can
be generated by a CAM program. Usually called CAD/CAM,
you can draw the part and generate the G-Code from one
program

I said usually and probably and most quite a lot because
all of the above is very general, and the lines are blurring a bit,
There are servo systems that take Step and Direction inputs
Stepper systems with feedback and thousands of steps per
revolution. AC servos, DC servos, bipolar steppers, unipolar
steppers, and a million others. Read the archives of this list and
you will probably learn more than any book can tell you. There
are some very sharp people here. Also go to the list FAQ
(Link at the bottom of email). Look around the web and you will
find some G-Code tutorials. It's really not to hard to understand
once you get the basics down, but like programming, things change
over the years. Look for parts on e-bay, swap meets, surplus sales,
wherever you are, keep looking. It's amazing what you can stumble
across if you have your eyes open. (can you tell I'm a pack rat?)


Hope this helps

Bill


catboat15@... wrote:

> Hi all:
> I signed up for this list to learn something, but find it way over my head at
> present.
> I was a computer programmer in the "good old days" Basic, Cobol and Pascal.
> Before we had little pictures on the screen.
> I have a 12 X 36 inch Craftsman/Atlas lathe and dream of drawing something up
> with one of my CAD programs and let the lathe follow to make what I want for
> my latest project. Is there a site or book that can be recomended to see if I
> am still dreaming or is this a valid idea?
> At the present time I use CAD print outs to paste to work pieces and follow
> them in that manner.
> TIA
> John Meacham
>