Not for a 12' to 14' bridge. That takes it pretty much outside the realm of the Homeshop/SmallShop world. Even using conventional electronics and controls will be a challenge with a plasma unit that cuts 4" steel. Just the noise impulse from the HF start at 300A is enough to stop pacemakers and kill small animals! You will have to make sure your electronics are noise "hardened". It's not easy to build a system with controls in a factory with the ability to test and find RFI and EMI problems. It's even harder to build one from generic controls in the field and without access to engineers and expensive test equipment.
We supply electronics packages for plazma and router tables and the size of the table is not so much the issue, but I have enough experience with trying to make PC based electronics work with big nasty, noise generating industrial plasmas to understand why the commercial tables charge 10X over the light industrial and home shop units. It can take hundreds of man hours finding and fixing EMI and RFI based noise problems. Often it takes innovative cabinetry (metal equipment enclosures) and other tricks to just keep the pierce cycle from killing the PC and low level control electronics!
I would not advise an amateur built table for this application. It would be like building a B52 bomber from lawnmower parts.
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