[eugenebrooks]

Maximize the distance between the TIG welder and the CNC equipment.

Connect the work piece directly to a good earth ground near the location
where the welder "ground clamp" is connected to the work.

Try and line up the welder ground cable with the torch cable to minimize RF radiation.

On the CNC equipment, encase all cabling in grounded shielding to minimize RF pickup from the welder and install a choke on the power input of the CNC electronics.

Adjust the spark gap on the welder to produce the minimum voltage needed to stabilize the arc.

Ultimately, if you can't provide the needed isolation you have to power down the CNC equipment when running the welder. These two pieces of equipment are not very compatible.

Eugene