This Instructable is not going to be a step by step build log of my machine, but an overview of my design and what I learned over the course of this build. Hopefully I can share a few things to help with your CNC build.
My frame design was based on various moving gantry CNC routers from around the internet, with a few alterations. I chose aluminum as my building material mainly because it was easily cuttable with the tools I had available, and I figured it would have much greater stability than a wood frame.
dbc1218's DIY-CNC-router build (http://www.instructables.com/id/DIY-CNC-Router/) guided me through most of the internals of the system such as the linear guide rails, ACME lead screws and nuts, and also with the CNC controller and stepper motors. If you want a step-by-step guide I would strongly recommend dbc1281's instructable.
Step 1: Frame Build
The frame was built using mostly 1/4in 6061 aluminum from onlinemetals. All of the aluminum cuts were done using a standard miter saw fitted with a carbide blade. Cutting was very precise, and quite fast, even when cutting 1/4x3in plate. A drill press was essential for this project. I learned very quickly that a center punch does not help at all with alignment of holes if you choose to drill by hand.
Step 2: Gantry
Linear System: 16mm steel shafts and bearing blocks (mainly from eBay).
I went with a 16mm linear system throughout the entire system, 13mm would have probably sufficed, and would have been much cheaper. 1/2in ACME threaded rod may have been overkill also. The only problem I have with this gantry is leverage. When pushing on the router bit by hand it easily moves ~1/8in in both the x and y direction. I may cut the height down a couple inches in the future to combat this problem.
Bosch Colt router mount came from k2cnc.com.