Dc servo motor control

So it should have 2 of those servo motors on the gantry, one on each side and another on the the X.
Do you have the schematics?

Yes there are 3 servo motors as described, I have 3 sets of cables coming from the driver boxes the same, the 2 x and the y. The 3 encoders feed straight back to the old control.

I have no schematics, I traced in the wires from the control used for the e stop circuit. There was also a safety limit switch below the left side of machine to cut the power, once activated it would not reset as normal, I had to open the switch casing to reset it.

Would you have any schematics? My machine did not come with any, perhaps others aee similar

No i do not have schematics, but i know almost everything about it, just have to make sure as it has been several years since i retrofitted the last of those.
Do not remove or disable that switch under the gantry, there is another on the X axis (short single one, gantry, that is X), those are "extreme limits" and in normal use they never trip.
The machine has proximity sensors an both sides and on X, wiring goes to a small box on the right side of the power box (outside the bog box, on the gantry near the big box, it is gray color about 15x8cm), and from there to the control box where the monitor and controller is/was.

Yes that is correct, the physical switches for safety and proximity for use. The proximity ones are exactly as you said, all going to grey box then signal to control. 

I have built a second gantry with a 4th axis from scratch for the same rails, I used 2x proximity sensors for gantry squaring, i would like this to do the same. I hope i can just use the existing prox sensors on inputs to the mesa to achive this.

on my old nce390 control the axis were turned 90 degrees, making the long axis the X with 2 motors, and the short axis with the head the Y, however on the second gantry I did make the short axis the x and the long the y and set new sheets in across the bed as it seems more intuative.

There was another switch for air pressure perhaps i can use this also on and input to the mesa just to bring up a warning.

It is the dc drives which I will struggle with, my understanding is the the encoders will feed back to my mesa, however the drives themselves have the 3 smaller wires each which all go into the single vertical connector that sits on a raised steel folded section above the board which the 3 separate axis connectors with the heavier gauge wire plug into. Im guessing by the caps on the board and the heavy gauge these are for powering the motors, what are the other 3 wires for? Are there motor enable signals?

Do not touch the drives, do not touch anything in the power box, only the control box wiring.
There should be 3 wires for the drives that will be wired to Mesa 7i77 or 7i97 analog outputs, there is another "enable" wire on another connector that has to be wired to the Mesa field outputs as it needs 24V, and there are the sensor wires to be connected to Mesa field inputs, and the encoders to mesa encoder inputs for each axis.
You will also need to add OR change the Z axis motor/drive, the original one was controlled via RS232 so there is no easy way of using it. Find another analog servo drive and add an encoder to the existing Z motor, or get a set of motor/drive. A stepper motor and drive can be used but it will require flashing the Mesa 7i77 or using a parallel port. The one i helped retrofit in France got a new stepper and ANALOG stepper drive made by Lam Technologies.

  I think the 3 set of 3 wires pictured must be for the motor control, one is to sheild. The go back through a 12 pin connector and to the controlI had started to disassemble the box before I read you posts, I had removed blue wires to connectors X3 and X5 on the boards, 2 came from estop circuit and another blue has also been left hanging from the  K1 contactor from terminal L3. If i had schematic i could make sure i have the 3 wires back correctly. The wires of course are ones with on markings!there is a 6 pin connector from the servo power supply board with 3 wires connected to in going back to the control, these go along with the air pressure switch wires, are these to pull on servo power?