CNC Panel Joinery from Make:
Here's a really useful article on CNC panel joinery methods by Make:..

Step 2 - The Cheapo Connection
Check here for our cross dowel nuts that are used in this tutorial. These are a great way to create joints in wood. If you are looking for some great CNC machine kits, look here. Making corners, connecting two pieces of MDF can be a challenge. I am going to run through a technique, and a vital element in the CNC machine of this tutorial. This step is not as glorious as building an actual working component of one of the CNC axes; however, this type of connection is used on almost every part of the machine. The idea is very simple: with two large holes to receive nuts, and two transversal holes to receive screws (long enough to reach the nuts), a tight and strong connection can be achieved. Not only is this connection strong, it also helps to create the tension desired to tighten an axis assembly around the rods/angles for snug no-play sliding. Other types of connections that I have tried are weak and prone to splitting. I have had no splitting or failures with this method.

John S.C.'s CNC Machine and Suggestions
John S.C. did something that I have not yet seen. He applied a ball-screw to the DIY version of the CNC Machine found on the step by step and the book "Build Your Own CNC Machine". Yes, you heard me right! A ball-screw. Why do I sound excited? Read on.