Building 8 x 20 ft CNC machine

Hi, am planning to build a 8 x 20 ft CNC machine using  servo motor. using 1 KW AC servo motor and 750W with the rated speed is 3000/ 6000 .1KW for X & Y and 750 for Z. I want to know if the AC servo motor can handle it and what type of mesa board to use and how to set the encoder to mesa board. 

Control cable pinout?

Yes, and the type of Mesa board to use again can the AC servo motor 1kw rated speed of 3000/5000 handle that 8 X 20 feet CNC table.

1KW is to much for any plasma, 400W will do just fine as you do need reduction.
An old Messer industrial plasma with 400KG gantry uses 2 of 500W motors with reduction.
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Pinout of the control cable?
We can not advise you on the board without knowing if the drives have encoder outputs.
If the drive has encoder outputs, Mesa 7i95T has step/dir outputs and encoders inputs, so everything you might need.

The driver has an encoder output. And what will the ratio of the motor reduction be is planetary gear reducer ok?

Yes it is, but beware of the cheap ones, those have a lot of backlash.
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If you can not find Mesa 7i95T, you can also get a Mesa 7i96S and 7i85 or 7i85S.