The NEMA23 motors you'll probably be using (less than 380oz/in torque) all have .25" shafts with a flat. To properly connect them to your leadscrews which I expect you to be using, you'll need the assistance of these handy connectors. We use the L-type connectors and they're excellent.
http://www.lovejoy-inc.com/products/...couplings.aspx
Here is an exploded view of how to couple the NEMA23's with the leadscrews by using the lovejoy connectors.
http://www.cncrouterparts.com/produc...products_id=58
Our team used this method (and the parts from that website) when creating our 4'x4' CNC routing table. It works excellently and we use it to manufacture a very large portion of our robots parts now.
You can see a picture of our router and some information on it at our thread about it here
http://www.chiefdelphi.com/forums/sh...ght=cnc+router
If you want more pictures of our router, you can see them in the media section of our website d5robotics.org, otherwise you're welcome to PM me with any questions on your build. Also, cnczone.com is a GREAT resource. Their homebrew CNC router section can be found here
http://cnczone.com/forums/forumdisplay.php?f=48 and their CNC mill section can be found here, with examples of conversions of common CNC mills like the Sieg/Grizzly micro/mini/small mills
http://cnczone.com/forums/forumdisplay.php?f=20
Good luck with your CNC builds, it's difficult work and planning, but once finished, you get a highly rewarding result.