Re: Need Help and Hardware to make CNC Lathe machine PC Based

I am in the process of converting a manual milling maching into CNC
myself, and converting a lathe into CNC is very similar.

The first componets to consider for your conversion will consist of
motors. Here you need to make a fundamental trade, stepper or servo
motors. Stepper motors are lower costs than servos, but for other
than the most demanding applications, today's stepper motor
technology will be adequate in 90% of applications. Assuming that
you decision is to go with stepper motors, you will neeed to decide
on the size and holding torque for your stepper. NEMA 23 or NEMA 34
are the most common sizes. NEMA 34 are physically bigger, and
generally are available with larger holding torque. But what is
most important and mostly ignored, is the power capability of the
stepper motor. (A good estimate is to multiply the rated Voltage x
Rated current for the motor). The larger the handling power of the
motor the better you will be. Keep in mind that the faster you spin
the motor, the lower the torque will be. (Toqure x speed also yields
power). For a Lathe conversion, I would imagine that a 300 oz/in
NEMA 23 stepper motors would be adequate.

Second, in order to control the stepper motors you will need a motor
drive circuitry (One for each motor.) There are several choices,
but if you are a beginner and like me and want to avoid problems,
you may want to consider the gecko drives. For steppers either the
G201, G202, or the new G203 would work just fine.

Third, Motors need a source of power, so you will need to have a
power supply. If a stepper motor is rated for example to a 3 VDC,
you will need a power supply with a DC voltage of at least 20 times
or in this case 60 VDC and a maximum of no more than 25 times or 75
VDC in this example. Although working with power supplies can be
very dangerous, it is not that difficult to make your own if you are
careful. To make your power supply, in addition to the desired
output DC voltage, you need to estimate the current.
Stepper motors normally draw 2/3 of the rated current if the motor
wiring is connected in parallel, and only 1/3 if connected in series.
So if motor is rated for 3 Amps, and the winding is connected in
series, expect no more than 1 Amp to be drawn. Multiply the number
of motors in your system to estimate the total current draw.
Assuming that you will have two motors, with a rated 3 Amps/phase,
with series-connected windings, then the total current needs will be
(2 motors/system x 3Amps x 1/3 = 2 Amps/system). So in this case a
65 VDC with a 2 A current capability would be adequate as a power
supply. An unregulated power supply consists of a step down
transformer a full bridge rectifier, and a Large filtering
capacitor. The step down transformer will convert the input AC
voltage (either 110 or 220 VAC) into a lower AC voltage. This lower
AC voltage needs to be 1.4 times lower than the desired DC output of
the power supply. So if you are going for a 65 VDC you will need a
46 VAC transformer. Toroid trasformers are very popular due to
their inherent design feature of being very low EMI radiators (very
low noise). The full bridge rectifier needs to be rated above to
the voltage and current needs of the supply, as well as the
filtering capacitor. The filtering capacitor needs to have a
voltage rating to at least 20% above the output of the power
supply. Typically a 10,000 micro-farad would more than enough serve
for this need.

Fourth, In order to interface the stepper motors to your computer
you will need a suitable interface. Assuming that you will be using
a parallel interface, then there are multiple vendors that have
parallel interfaces, many of these are opto-isolated to prevent
damage to your computer in case of wiring problems. Some of the
Gecko drives are already opto-isolated, so you do not need for the
interface board to have this capability. (not all Gecko drives have
this feature in all pins, so be careful).

Fifth, The parallel to motor drive interface will also need a DC
voltage source, typically this will need to be 5 VDC. I normally
use an old PC power supply, which has 3.5, 5, and 12 VDC readily
available. You will need a box or chassis to house the unregulated
power supply, the motor drives, the parallel interface circuit, and
the regulated power supply (5 VDC). All of these components may
generage substantial heat, specially the motor drives and the
unregulated power supply, so a set of PC fans can help you keep all
of this circuitry cool.

Sixth, you will need a design approach to interface your setepper
motors to the screws in your lathe. Here you can use the existing
ACME screws (I am assuming that this is the case), or you can
upgrade to the more accurate but far mor expensive ball screws.
Ball screws when properly designed and installed will be more
efficient, and will have smaller backlash.

Seventh, You will need a software package to comand you motor
drives. Here one of the most popular hobby type controllers is MACH
3, but there are many other programs available. This program will
take G-code, and command your motor drives into setep and direction
pulses.

Eight, What generates G-code. Well you can painfully generate it by
hand (the very old way), or you can have a computer program generate
it for you. This is the function of a CAM program. CAM programs
take a drawing (from a CAD) program, and optimize the tool path and
other parameters such as feed rate, feed cut, etc. and the ouptut is
a G-code file to be taken by a program such as MACH-3.

Nineth, You need a CAD program to design your parts. Here there are
many many options, with many many price points. You could end up
spending more for top of the line CAD program than the entire CNC
conversion, so depending on you budget, preference, and needs you
could have many options.

As far as sources for materials, many web sites have links that can
be used to do your research.

For stepper motors you can start at: http://www.homeshopcnc.com, the
use their links to follow other sources.
for motor drives try http://www.geckodrive.com/
for toroid transformes try : http://www.toroid-transformer.com/
for complete power supplies try: http://stores.ebay.com/Antek-inc
for computer to controller interface circuits try:
http://www.cnc4pc.com/
for MACH-3 try:http://www.machsupport.com/

And the best source of CNC information is www://www.cnczone.com

I hope this helps. It took me a while to find the above
information, and I would like to share the little I know with anyone
that is just starting out.


Remberto

PS. To anyone with more experience, please add/correct to the info
I have included.


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Zahid Liaqat"
<miassint@...> wrote:

>
> I have a Harrison Lathe machine TRAINER 280 CNC/Manual.
>
> The manual mode of machine is working perfactly but its CNC mode

is not

> activated due to damage e-prom software of its one board that is

the

> main interface between the Acorn computer and all the control

switches.

> The card is made by "BRADFORD INSTRUMENTS LTD. 060/04 1986

England",

> the 64k eprom IC # is TMS2764-25JL and the label on the IC

is "Lathe(m)

> Ver.2.02". I tried to arrange the software by internet but fail.
>
> Now i want to swap my Lathe over to a modern PC, Gecko/Rutex

drives and

> driver software such as Turbo CNC or Mach 3 which i have

downloaded

> from internet.
>
> Now plz tel me From where i can get good hardware and complete

GUIDENCE

> to complete my task.
>