CNC Machines can come in many shapes and sizes. Just look at these cool instructables on building a CNC. This is a cool new instructable how to make a CNC using pipes, which blew me away. There is also this one that includes plans.
This instructable is based on a logical process of construction where measurements are made during certain steps to achieve any size CNC machine. Whether you want to build a mini mill for PCBs, or a large sign making device. It's up to you. With power tools, I believe that this machine can be made in one weekend. I built mine within two weeks with kids, wife and a job. I just wish I had a table saw to replace my miter box (you see me cranking away in the videos). The cool aspect of this build is that you can put the thing together as you create the pieces.
So, we left off with the z-axis assembly and now we can get started with the y-axis.
Step 1: Make the Y-Axis Bearing Supports
First I will cut the y-axis rail support piece by taking a 7" wide piece and chamfering the four long edges to receive aluminum angles. The 7" measurement will dictate the z-axis travel. If you want more z-axis travel, use a wider piece. We will need this piece to make other measurements.
The two bearing supports for the y-axis will be cut about 5" to 6" in length using a 4" piece of MDF. These two pieces will slide along what I call the y-axis rail support. The bearing supports will hold the bearings with grooves cut out of the MDF.