I use the qualifier “commercial-grade” here because this TIG welder project goes far beyond our junkyard TIG welder. The welder has a 180 amp capacity and has most (if not all) of the features of a modern welder. Instead of using a microprocessor, Dave Barrett decided to use discrete TTL and CMOS logic. That decision should make the design a lot easier to troubleshoot. Schematics and board layouts are on his site.
[UPDATE: I forgot to thank demmion for the tip]