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).
Acme 1/2in 2-start threaded rods (mcmaster.com). Couplers, anti-backlash nuts, shaft collars (dumpstercnc.com).
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.
Step 3: Electronics
Controller: Gecko 540 and power supply from automationtechnologiesinc.com
Motors: 3x 280oz/in Gecko Stepper Motors
Computer: Old pc with parallel port
Router: Bosch Colt variable speed.
Software: LinuxCNC, Autodesk inventor, Inventor HSM express.
The g540 isn't cheap, but it is reliable and easy to set up. I initially thought about purchasing software to control the CNC, but chose LinuxCNC instead. It comes with tools to setup the g540 in no time at all. I chose the Bosch Colt because it was fairly cheap, and well liked on the internet. Autodesk provides a 2 year license to students free of charge, an extension called HSM express creates gcode files for linuxCNC very easily.
I also purchased an aluminum box from automationtechnologiesinc.com. It is a bit expensive but comes with a lot of nice features in a nice looking box.
Cable Carriers are from ugracnc.com
Step 4: Conclusion
Final build cost was around $1500. The router cuts wood great, and will do aluminum with Cut depth around 1/32in at 15in/min. The build ended up being more expensive than I was hoping, but it was a good learning experience.
As of now I am using double sided carpet tape to hold pieces to the table, and haven't had any problems with that.
I am not using homing or limit switches. I find it much easier to just home the axises to the edge of my project each time.