Just to give a little update to this thread, I actually went and bought a very cheap adcock and shipley horizontal milling machine on ebay instead, ahem.

It is a production style machine, so pinion/rack on the x axis, and also not on the z-axis, but the y axis at least has an acme lead screw with 0.001" backlash.

Compared to my old centec, this machine is in way better condition, with no discernible play on the table, but obviously the x and z axis have to be sorted for it to be sensible.

I'm currently in the process of converting the x axis with a m16 threaded rod (i know, i know), as it's what i had lying around. Obviously not ideal, but a huge improvement on 1 turn = 5 inches :)

My plans for the machine is to use the horizontal part as a little lathe (er40 collet to hold a bit of bar), and i'll also make something to hold a small lathe chuck for non circular work pieces.

I'm also going to build/bodge on a vertical head of some sort, with built in travel, as that essentially sorts the z-axis issue (I can move the z-axis, but it requires gorilla strength).

Might keep this machine as a manual one and use it to build the parts required for a CNC machine, as suggested earlier in the thread, as I'm guessing it's not ideal for CNC conversion, given that the table doesn't sit on rails etc.

As for CNC machines, I'm thinking of starting off with a CNC lathe instead of a milling machine, seems more useful for the bits I need doing for my car hobby.