I gather from a couple of hours reading threads on here that I need to add certain words, Marchant, Dice, Gantry, unsupported-rails, and so on to the list of naughty words.

I need to get some real time with the machine to understand if it is up to the job of PCB routing - gantry style machines do offer a good x/y size for the price, however, if the machine is fundamentally flawed, and will never give the necessary accuracy then I'll cut my losses early and look for an alternative. Some of the results from analysis on these forums for the deflections on unsupported rails is truly shocking and I'm concerned now that it won't give reliable/repeatable engraving at the depth of the copper on the copper clad board.