Quote Originally Posted by flanagaj View Post
The main use will be for machining timber panels for furniture and timber for boat making. I would, however, like to have the flexibility to be able to machine alloys as well, so having an accurate machine would be ideal.
If it's mainly for wood then that sort of accuracy is not going to make an appreciable difference. £800 sounds a lot ... invest it in profile rails etc. How can you be sure that after the frame has been machined when you fix it to the floor it does not distort.

Getting the rails parallel is not a problem - once you have the gantry mounted and put a couple of bolts in one rail the other will self align. Either that or you can use a DTI to align them by affixing it to one carrage with the needle against the other rail.

Another way to get them parallel in the vertical plane is to mount them on (the right type of) epoxy. Pour the epoxy on the rail mounting surfaces with a channel (or several channels) in between and gravity will level it 'automatically' with very high accuracy.