I want to build a plasma cutter

Maybe go all out and build a big gantry for the arm and you've got one of these

m.youtube.com/#/watch?v=jv2lncfWO5U&desk...ch%3Fv%3Djv2lncfWO5U

Also I'd second the hypertherm plasma if you find you need a new one of want too upgrade I think a power max 45 would do for 1/4 maybe the 65 tops

We've got the 85 and its brilliant we've cut plenty of 20mm on there and it's spot on the trick is to use the lowest amperage setting and feeds for that thickness if you get the hypertherm owners manuals they have the cutting charts in them with a range of nossels and amps and speeds like I said the lowest gives the best cut but if the machine can run as quick as needed then the highest can be gotten away with, with very nice results too

Also we've got a downdraft bed on our esab gantry and if you start the program without the fan running you know about it very quickly can soon fill our 9500sft shop with fumes