Threaded bar, steper motor and a plasma cutter.. your thoughts?

[Jonathan]

These guys do some great prices on bearings too (their belts and pulleys are competitive as well) - VERY handy.
Much appreciated

Bearing station's prices on the timing pulleys work out better than beltingonline by the time you include VAT and delivery, although if you've not got a lathe to bore them it may be worth paying the extra and using beltingonline.

You're not going to get anywhere with 8mm threaded rod. Even if you use pulleys to have a high ratio between the motor and screw, to compensate for the low pitch, you're still not going to get a very good speed because the efficiency of the drive system is so low. Driving the X and Y axes with a belt directly may be the way to go since the forces on the head are low, so the lack of rigidity with this system isn't such a big deal so long as the gantry is quite light.