Hi Andy.
Nice machine. I see what you mean about the over kill for the plasma, thats a big gantry.

I would like to change the design of the gantry so I can use supported round rail because it is a lot cheaper than the Hiwin Rails, but not sure how I will mount these.......
You can get double slot profile to be able to mount the supported rail but this is obviously bigger and heavier than the 30mm you planed to use. I would think about using some more steel box for the gantry, smaller thin wall would be about the same weight as the double Ali extrusion and much cheaper.

You could also look at Ali box and tap it or use a tapped steel plate on the inside to bolt the rails to.

I was thinking about using rack and pinion for the x axis but I am all ears to any other suggestions
Not used it myself but I think its what most people use for long lengths, don't forget belts as well, both suffer from poor resolution so if you need 0.000000001mm accuracy :heehee: then it will need gearing. But don't forget that this will also improve the rapids so a balance over resolution and speed needs to be considered.