Cutting forces and Acetal nuts

Hi all,

I've been reading this group now for a while and I am impressed with
all the knowledge here! It's great!

I want to build a CNC router/milling machine, bridge type, 600 mm x
420 mm work space (that's about 24"x17"). I'm aiming for
repeatability better than 0.1 mm (that's about 0.004") and total
mechanical accuracy, well, something like 1 mm (0.04") over the whole
working area.

I want to be able to cut wood, MDF, Delrin, perhaps make my own PCBs,
and preferably also cut aluminium panels and the like. I'd also like
the total cost (for lead screws, servo motors and MDF for the frame)
to be <$1000. Cutting speed is not important; this is a hobby
project. I will try to build servo amplifiers myself since I'm into
electronics.

So, does this sound reasonable?

... and if so, what kind of lead screw do I need?

I'm leaning towards BS&A's 16 mm dia, 4 mm lead leadscrews
with "Advanced Anti-Backlash Supernuts". (I can get them locally, in
Sweden, for about $300 - that is for 3 pieces, 35"+23"+11" long, and
three "supernuts". Add to this the cost of angular contact ball
bearings and end treatment of the screws.) What I am worried about,
and have not been able to find much information about, is what kind
of cutting forces that can be expected from the kind of work I want
to do. This particular screw (or nut, actually) has a "design load"
of 175 lbs (or about 775 N if you prefer). Will this be enough, or am
I going to destroy it milling aluminium?

Thanks for your help

// Arvid