Re: retrofitting an older CNC

R Rogers,

I couldn't bring up the picture of Peter's mill so I don't know
exactly which model it is. I have a pretty good idea though.

Here are some of the reasons why I think it would be foolish to
replace such a powerful control.

The machine probably rapids in the 300ipm range.

The Dynapath control is considerd very reliable, I suspect his
current Z axis problem is related to the axis drive not the control
as such. The factory gives phone support on control problems. This
control can also be upgraded to their latest and greatest with a kit
from the factory.

The most important reason not to retrofit is the feature list of the
control. Helical milling, graphics, axis rotation, axis scaling &
reversal, conversational & Gcode (intermixed) programming, macro
programming, 3 axis arc cutting (not just in the XY plane), canned
cycles for circular & rectangular pockets, bolt circles, rotate and
repeat for symetrical pockets, subroutines, arc & cam milling, polar
coordinate programming, concurrent programming (while another
program is running), calc assist, buffered input through RS232 port,
industry standard Mcode interface to an auxiliary device, etc, etc,
etc, etc. The list goes on, these are just the features I can
think of quickly. They're all standard on the basic control, maybe
his control even has some of the really magic optional stuff? Can
any of the "hobby class" PC controllers come anywhere near this in
features?

Doug





--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
wrote:

>
>
> no falloff <nofalloff@y...> wrote:
>
> After using CNC mills both at a friends shop, and as school, I

decided I just had to have a machine of my own. After saving for the
better part of a year, I just bought a CNC Shizuoka mill with a
Dynapath Delta 20 controller (pics at: www.cyclegarage.net/mill).
I'm not sure if the controller is any good. It seems to work but I'm
getting a fault on the Z axis. I bought the machine figuring that
the controler wasn't working, and had planed to replace it (of
course only knowing enough to be a danger to myself and others :-
) ). It seems retrofit controller systems by Centroid, and Anilam
etc. are way too expensive for my current budget. I was hoping to
use as much of the existing hardware (servos, servo amps and
electronics) as possible, and just use a PC as the controller. The
mill is currently fitted with Baldor permanent magnet servos. The
book for the servo drives (the only documentation I have) mentions
that the drives are looking for PWM signals from the controller. I
know that

> one could probably write a book in response to my questions, but I

just need a general bit of clarification.

>
> Get a Dell 2.2 Celeron for $349 delivered. Install Mach2 $150 on

it (runs very smooth) Use Gecko 320's for your drives $114 a piece.
Bob Campbells PC to Route breakout board $130 or so. I just
retrofitted my Bridgeport from an old Bandit stepper system. I used
Allen Bradley Servos and I use this machine everyday and dont have
one complaint with it. To date it has not lost a single step to my
knowledge nor has it made any unexpected movements on its own. Mach2
is a very easy and reliable program with alot of features. The nice
thing about it, It's user adaptable. If you want to do simple tasks
you dont have to be a PC whiz to perform work with it. It has alot
of advanced features but, If you dont want to deal with them you
dont have to. I have some pics of the enclosure and the control
interface that I built. If you are interested let me know.

>
> 1. Systems that use gecko drives don't have absolute feed back?

That is, the computer sends motion signals (step and direction) to
the drive but has no way of knowing if the servo is in the position
it is supposed to be in? How does this compare to the positional
accuracy as compared to the current system?

>
>
> Yes the G320 servo drive uses feed back. Through an encoder. The

best thing to do is just replace the existing ones. US digital has
an E5S-200 with the proper Ma draw suited to the Geckos for about
$40 a piece. The reason I favor the 200 line quadrature is: with my
2.5:1 reduction on each axis every step equals .0001 of an inch
exactly. So 10,000 steps per inch and Z is 20,000 steps per inch.
The accuracy with mine is daunting. .0001 resolution, checked it
with an indicator it is there. Not just numbers on a screen. One
good reason to replace the encoders is for safety's sake. If you
lose an encoder on a DC servo system the axis will run away and only
stop when it crashes or hits the limit switch. always be aware of
this.

>
>
> 2. Does the fact that mach 1 uses step and direction commands mean

that it can't be used with the existing servo boards in this
machine? If not what controller software (EMC?) would work?

>
>
> It isnt worth toiling with. Throw the old junk out.
>
>
> 3. How do I interface it with the existing hardware? If the servo

amps don't except step and direction signals, then I assume that a
simple breakout board such as those used with gecko systems won't
work. Likewise anyone have suggestions as to what will?

>
>
>
> 4. These servos are rated a 120v and 10A (continuous) 39A (peak).

It is my understanding that these can be used with gecko 320 drives,
but will not achieve their maximum rated torque or reach their
2500RPM max rated speed. Is this correct? Will the tachometer need
to be replaced with encoders in order work with this system? Rutex
drives seem a better choice, true?

>
> The Geckos work perfectly on my Bridgeport. No heating

problems..nothing. And I'm driving the knee with a 40 in/lb. motor.
I ran a profile program that was 2 hours long (30,000 lines of g-
code) and the Z was whipping up and down the whole while. I did it
to test it. The motor got a little warm but the Gecko on a heat sink
with a fan was hardly warm at all.

>
>
>
> They must be DC brush-style motors
>
> I'm using 100 volt servos, 13.7 amps continuous and 26 amps peak.

As long as you supply the necesary amperage you will not lose any
torque. the Geckos are rated at 80volts and 20 amps. My transformer
is putting out measuring from the bridge rectifier about 68 volts
DC. Measuring off the transformer it is less due to the RMS. But you
will lose some speed and on a vertical mill. who cares? 2500 is way
too fast even for a 3:1 reduction. the voltage from your existing
power supply will be too high for the Gecko's, So the output will
need to be changed or change power supply's. www.cnckits.com has
them for about $400 dollars completely wired and ready to go.
$h*tcan the tachometers, you dont need them. One important thing to
remember: Use two pair sheilded cable and run A and B channel from
the encoder in separate pairs and keep the encoder cable as far away
from the motor leads as possible. They will crosstalk and give you
fits if you don't. This means two separate plugs on the servo

> motors and the control enclosure.
>
>
> Lastly. How hard would it be to include the stepper motor

controlled spindle speed, and tach into the new controller? Could
this be done by defining it as say a 4th axis?

>
> As I undertstand it. Bob Campbell who makes the Breakout boards is

making an auxillary board that plugs into the breakout board for
spindle speed. I'd like to have that myself. Or you could always
incorporate a small DC servo and run it as a 4th axis. But the
programming would be more difficult. I'd just wait for Bob's board.

>
> I've been searching and reading as much as I can, and have royally

succeeded in confusing myself. Any links and information I get I
plan on including on a page on my web site covering everything I do
to get this machine running. I hope to document everything I go
through, as other who have done so are what inspired me to try this
crazy stunt. >:-)

>
> The most difficult portion of your retrofit is going to be the

Power supply. Many on the board here can help you with that. They
did with mine and all of the info I received was right on the money.
The rest of the components are "plug and play" practically.

>
>
>
> Thanks in advance for your help.
>
>
>
> Peter-
>
> pdh@k...
>
> (remove knowspam to reply)
>
>
>
>
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