Re: DON'T CUT THOSE WIRES !! and My CNC Mill retrofit project

[I got some knowledgeable responses to my plea for help with the proposed
"brain transplant" for my old CNC mill. They are all bundled into the
following mega-reply. If this messes up the archiving structure of the
list, let me know, and I'll go back to replying separately to each message.]

Andrew

Date: Wed, 13 Oct 1999 03:29:50 +0200
From: "Arne Chr. Jorgensen" <instel@...>
Subject: DON'T CUT THOSE WIRES !!

Hi,

I had already turned off the machine, and I am crazy to fire it up
again. ( I should have been in bed )

Is it Andrew who have this Loveboy - something ? ( I have no time
to find out who said what, and to whom )

[I call it "The Beast". (We'd have to be on better terms before I started
calling it "Loveboy".) Actually, it's a Ramco/Leadwell with a Lovejoy AC
speed controller.]

But, I think it is wise not to cut wires, and first try to see if
the machine can work as it is. TTY is teletype port, and yes, it
is a current loop, most of the time.

You can feed G-codes from any program and computer. These often
used paper hole tapes, and don't always have a high baud rate, but
- it is so much faster than the movement of the axis anyway.

[I thought of trying this, but the machine's controller seems to be in such
a fragile state of health that I figured it would be best put out of its
misery. Doing this, I can easily see getting into a situation where I
wouldn't know what was screwing things up- the patched-in drip-feed, the
old computer, or the associated maze of circuitry.]

I have always found that it is very wise to try to get something
running as it is designed, before doing modifications. If you want,
I can probably give you a few ideas. Old ISA board IBM serial
cards, do have this current loop, on the normal RS232 DB25
connector. There should be no problem to download programs. At
least I can tell you how to wire the serial port card.

//ARNE

[Sure, I'd like to hear about that. It certainly would be the cheapest way
to go. There are a couple of RS 232 ports, but they aren't connected to
DB-25 cables- they have round plugs instead.]


Message: 4
Date: Tue, 12 Oct 1999 20:43:19 -0400 (EDT)
From: stratton@...
Subject: Re: DON'T CUT THOSE WIRES !!

> But, I think it is wise not to cut wires, and first try to see if
> the machine can work as it is. TTY is teletype port, and yes, it
> is a current loop, most of the time.
>

If he can find the level shifter chips on that TTY port we could
probably figure out if it is current loop or normal RS232. For
example, if they are 1488's and 1489's, I'm guessing they would not be
current loop but rather normal RS232 signalling.

["Level shifter chips"? What do those do, and where would I look for them?
As I mentioned above, there are some RS232 connections- what does that
indicate to you? Could you explain the difference between current loop and
normal RS232 signalling?

I looked into one of the motors, and was surprised to see only 4 contacts,
2 of which seemed to be the DC current + and - and 2 which came from a
gizmo on the back which I assume was the encoder. If the things have
tachometers they are must be someplace else- or can speed be calculated
from the encoder pulses?]

IO ports being
pretty robust, I would think it safe to use the continuity check
function of a modern digital multimeter to determine what chips are
connected to the connector (particularly pins 2 & 3) while the machine
is powered off. Often though it is visually obvious what they drove
the port with.

Chris

[So once I'd located these chips, what then?]

--
Christopher C. Stratton, stratton@...
Engineer, Instrument Maker & Horn Player
(978)538-5179 work, (617)492-3358 home
30 Griswold Street Cambridge, MA 02138
http://www.mdc.net/~stratton

>Message: 5
> Date: Mon, 11 Oct 1999 09:21:23 -0500
> From: Ray Henry <rehenry@...>
>Subject: Re: My CNC Mill retrofit project
>

[snip]

>[Punch tape? You've got to be kidding. I suppose it might be possible to
>run it on mag tape, but that stuff's prone to errors. And the thing is
>really senile- I know that even if I manage to trick it into starting
>properly, as soon as I get something going on it , it will crap out
>absolutely. I'm interested in running programs that are more than a
>megabyte, and I just don't think this old control system will be able to
>execute them reliably.]

I didn't mean to suggest that you would run punch tape rather that you
could use the punch tape input to feed commands to your machine. Many of
these older machines had a switch that would allow them to run directly
from tape -- hence you could slip any 8 bit parallel signal to the control
through the tape in wiring. A while back I prototyped a cable and software
to run g code through the parallel port of a pc to a tape in on an old AB
7300 cnc. The cnc would accept all of the code that it needed and then
pause the parallel port.

[That sounds like a promising approach. Do you have any of these
cable/software kits you'd be willing to sell? I'd like to try this, if I
can coax my machine into booting up all the way. Currently it won't accept
any commands, although I can hear relays working- maybe replacing some (or
all) of them is called for.]

<snip>

>4. If it goes belly up once in a while - blank screen, milisecond overlaps,
>non operator or program related crashes - these needle in the haystack
>kinds of failures can often be traced to aging contacts and aging
>capacitors. Some of these may be in the power supplies others in the brain
>others in the drives others in the interface circuits and wiring. The
>specific nature of these kinds of failures should determine how far you
>need to go with the retrofit.
>
>[These are more the sort of problems I've noticed. Lately, it has only
>managed to boot up halfway, and won't accept any commands- if it's alive,
>it's in a coma.]

To bad I don't need a vacation in Oakland.

[What? EVERYBODY needs a vacation in Oakland- if only to make people
appreciate their own hometowns.]

>When I do this, should I send you the old control computer? ]

My wife complains that I've already started a metalworking museum. (but I'd
like to know who made the control. Any tags on it.

Ray

[I'll check, and get back to you. I did find out that my servo amps were
made by "Westamp Inc." if that means anything to anybody.]

Message: 8
Date: Wed, 13 Oct 1999 01:06:06 -0500
From: Jon Elson <jmelson@...>
Subject: Re: DON'T CUT THOSE WIRES !!

stratton@... wrote:

> From: stratton@...
>
> > But, I think it is wise not to cut wires, and first try to see if
> > the machine can work as it is. TTY is teletype port, and yes, it
> > is a current loop, most of the time.
> >
>
> If he can find the level shifter chips on that TTY port we could
> probably figure out if it is current loop or normal RS232. For
> example, if they are 1488's and 1489's, I'm guessing they would not be
> current loop but rather normal RS232 signalling. IO ports being
> pretty robust, I would think it safe to use the continuity check
> function of a modern digital multimeter to determine what chips are
> connected to the connector (particularly pins 2 & 3) while the machine
> is powered off. Often though it is visually obvious what they drove
> the port with.

If it IS current loop, pins 2 and 3 are likely NOT the signal pins.
There's not a standard as commonly followed as RS-232 for the
pins used for current loop. Many systems don't even use DB-25
connectors for that. The standard was 20 mA for a 1 bit (same as
-12V for RS-232) and no current for a 0 bit (same as +12V in
RS-232).

Jon

[So it seems like my problem will be first to figure out if the RS232 plugs
are carrying my signals- if they are, then it would be +/- 12v, right?
(I'm assuming the signals we're talking about are position feedback and
tachometer output, correct? If someone wants to explain the difference
between "current loop" and "normal RS232", that would help.) If the RS232
connections are doing something else, then I should start looking for this
20mA signal? If it isn't connected to pins 2 and 3, where would it be?
Would it be one of the TTY connections? Forgive me if I seem a bit dense,
but I'm way out of my area of expertise here...]

Andrew Werby

Andrew Werby - United Artworks
Sculpture, Jewelry, and Other Art Stuff
http://unitedartworks.com