X2 retrofit x-y bed

[duce00]

I have downsized my origional plan to build a large CNC router and Im designing a larger X-Y bed for my X2 instead. Since I got the CNC bug Ive been collecting bits and peices (yeah Im a steel yard hound). Right now I have 1.5 precision ground ball screws from a Mori Seiki lathe (yes, I really mean 1.5). One is complete and OAL is 27.875", it also has bearing blocks and bearings. The other is broken and OAL is 26", it only has non-driven end block with bearings. They are definately oversized for this application but dang they are nice and only 17 cents a pound! No backlash, rough spots in travel or bends (even in the broken one).
So I have made some basic models and I think I have a fair idea on how to use them for the Y and Z axis. The broken one can be turned at my college shop (we have manuals and CNC) and it will be the Z. The complete one will be the Y. But here is where all my plans start to unravel...I still need an X screw.
After much research and Ebay watching Im starting to get a little neurodic and its really starting to irritate my family. Maybe you folks can pitch in on this one. Heres some of my questions and general issues.

1) I really want to make my X-Y axis screws the same pitch (5mm) but is it a cardinal sin not to? Can I use a 10mm pitch X screw and a 5mm Y? The 5mm screws that are in the lengths and grade I am looking for tend to get too expensive and I am working on a tight budget. What are the real problems in doing this?

2) Does anybody have some straight info on ball screw maintenance and reconditioning? I dont mean re-grinding obviously. I mean cleaning minor pitting and cleaning. Also nut disssasembly and repacking. What kind of grease is used anyway?

I could throw a few other questions out but maybe I should shut up and listen for a bit.

[Crevice Reamer]

What size travels are you planning to have?

CR.

[duce00]

The complete screw has 17" threaded with 4" ball nut. Im shooting to maximize that for the Y axis, so after all is said and done hopefully 12" Y travel.

The screw that needs to have the end refinished is going to be the result of what I get after designing its drive end bearing block. So with 16" of thread, about 2-3" of end finishing and a 4" ball nut I hope to get about 9-10" of travel on the Z axis.

The X axis is where Im really struggling. Like everybody, I want all the travel I can get. What I think is reasonable with a completely redesigned base and ways is around 26-30".

I am looking at belt driven systems to alter the X axis drive ratio to match the screws I have, making 5mm on all axis. This would solve the pitch compatibilty issue but raises the backlash question. Right now 2 of the 3 screws needed are high grade and it would be silly to have an X axis that was not able to match those tollerances.

Im still working out the models but after a few false starts on a CNC router I am trying to hold on letting the design exceed my understanding. I can design and model anything but that doesnt mean it will work or be affordable. There in lies the rub!