I originally built my table with a Cut40, HF contact start torch (chinese made cutter). It caused a lot of problems and took a little planning to eliminate them. Make sure ALL of your electronic components are electrically grounded (power ground).Then I used shielded, twisted pair wiring with a drain wire wherever I could (all switches, etc.). Make sure that ONLY one end of the drain wire is grounded to the table. Then I sunk a ground rod for the table and connected it with 6 GA wire (ground wire to table frame). This should take care of most of the HF noise.
Even after all of this, the PC still occasionally went nuts or locked up. I finally had to move it about 20' away from the table. Once I did all of this, the table ran fine with no problems. I've since upgraded to a Hypertherm Pmax65 and could finally move the PC back near the table. You can make it work and it's probably good to use all of the extra grounding even if you don't use a HF start torch. I know that I won't have ant problems now.
You can look at my build "A Different Machine - Downdraft/water table". Might give you a few ideas.
Good luck with your build.
Willy
P.S. I also grounded the cutter case to the table. Don't know if that helped any but it didn't hurt.