MG Tracer Gantry Salvage

[hybidder]

I just bought an older MG electric eye tracer gantry (no table) with four torch stations (two with machine torches in them). My initial plan was to cannibalize (no offense to any practicing forum members) it for the rails, racks, pinion gears etc to build a small homebrew CNC plasma table.

The machine model is PC750 and has lots of functions I would have never thought of such as the auto-igniter, solenoids for high and low preheat oxygen and fuel gas as well as of course the cutting oxygen for each of the 4 torch stations and each station has a rack and pinion powered height adjustment (not auto, just toggle up/down)- all from the control panel. I plan to keep two torch stations and setup one for oxyaccetylene, the other for plasma and probably sell the other two. They would make a great Z axis since they have guide rails and servo motors already setup with the bearings already in place for the X axis to attach to a piece of .5" x 4" cold rolled flat.

My salvage plans might be changing. This afternoon I took a few minutes to look it over and dig through the two boxes of parts that came with it and found the control head and cables. I bolted it back on the machine and connected power, and you guessed it- It's Alive... The gearmotors for both axes run smoothly, the four torch heads power up and down and even the auto-igniters buzz (no spark plugs in them). It looks like this 18'-9" beast can be put back into operation with a little work to build a table and just a little more luck.

My thoughts are now running along the lines of either using a dual operating system, one original, the other CNC using the existing servos and addiing encoders in line with the existing tachs. Either that or figure out a way to interface the electric eye with the new CNC setup, if the eye proves to be fully functional which it seems to be.

My question is, how does the electric eye work? It lights up and when you hold a momentary switch in the up position the head spins. I drew a thick black line on a piece of paper and it will move the torch heads left or right and when I rotate the paper 90 degrees the other motor (what I would call the Y axis if it was a mill) runs. I guess I'm trying to figure out the actual starting procedure for lining up the torch head with the drawn pattern in order to initiate a cut?

[Al_The_Man]

There were some of these similar tables that were converted to dual mode, but most users that converted, just went over to almost 100% CNC use.
The down side, of course to a tracing table is that it takes double the work space.
Simply, the principle of the trace is that the retro-reflected light back from the table is received by a photo-cell that oscillates, therefore if the reflected image back straddles the line, a sine wave with equal amplitude above and below the zero line is output from the Photo cell, If the head relative to the line moves off course, the sine wave zero reference moves up or down and a correction signal is sent to the servo to maintain the sine zero balance.
It is alot easier to explain with diagrams.
Normally a spot light allow the initial lining up of the head, and when the start button is pushed, the auto trace takes over, if a valid line is read.
The set up of the head is critical, initial hight etc.
Al.

[jcc3inc]

Sir,

You have a Stewart Warner tracer. It uses photocells and a small motor driving a timing belt to rotate the eye assembly. I believe the output is from a sine-cosine pot yielding DC voltages to go to the servo amps. I think it will run around 60 IPM, depending on the rest of the machine. The scanner has left-right offset capability (kerf compensation). You may be able to get info from MG Cutting Systems. The system worked quite well.
Likely the motors drove Bison gearboxes; they are good quality. Ther Stewart Warner tracing and drive systems were competitors of ours.

If you had the instruction manuals for the tracing system it would be a great help!

Regards,
Jack C.

[hybidder]

Al,

You're correct regarding needing twice the space and that's a big drawback for me since in order to get about an 8' x 5' cutting capacity I'll need an area of about 20' x 20' by the time I allow enough room to maneuver a forklift to load it.

jcc3inc,

You're also correct, it is a Stewart Warner tracer and controller. The speed also seems to be in about the 60 ipm range. I found a website for MG and sent an email regarding info/ manuals for my machine but haven't had a response yet. I'll give it a couple of days and then call if I don't hear from them. I'm glad to hear you think they are decent machines.

There's a small broken light (looks like it might have been neon?) on the front of the tracer head. Is it just a power indicator or does it show when the tracer is locked on?


I tinkered with it a bit more today and blocked up a piece of plywood to hold my pattern about .5" from the tracer head. When the straight line pattern is parallel to the gantry the X drive moves the torch heads and if I slowly rotate it toward the perpendicular of the gantry the Y drive incrementally increases and the X seems decrease in proportion to the Y. I think the machine might just be good to go once I fab a table for it.


Thank you both for your input.

[jcc3inc]

Sir,

If I recall correctly, there was a light on the scanner that indicated off-pattern. Inside there were (3 ???) lights that illuminated the pattern using a dual purpose lens, the outside was to focus the lights, the inside to focus the reflected pattern onto the photocell. Also, the system was likely BOTH a silhouette and line tracer. Somewhere you could elect line or edge (silhouette).

Where are you located? Again, it would be very desireable to have the schematics and operaotr's manual.

jccinc at owc dot net

Regards,
Jack C.