I have been working on a low budget CNC machine design on and off for a couple of years now. This has resulted in my 3.rd design iteration, by which I consider the design done.
It's a low budget machine, so don't expect high speeds, precision and metal capabilities. I have routed stuff requiring <1mm precision without any problems though.
I managed to keep the complete build below 200$ here in Denmark, and I guess it could be done cheaper elsewhere since prices are in the high end here. The price includes everything: nuts, bolts, wood, stepper motors, electronics, dremel tool (a cheaper copy of a dremel that is) etc...
I have made a BOM, some description, packed all necessary drawing files and taken a lot of detail photos of the machine. It is all available for free on my webpage: Low budget CNC – nengineering
The work is released under a CC license, which you can see on the webpage as well.
I really hope the design will be of use to some of you!
How are the u-bolts doing on your gantry? I was initially going to use u-bolts on my panel saw, but made bearings from 2x2's. I've got my frame and carriage built and all I need to do is put it together which I can't do yet, but I might switch to the u-bolts on that later.
They are doing fine! I have built and tested 10 of the latest design to validate the design. And if one have in mind that the machine is not intended for precision work it works quite well! This includes the choice of linear rails made with the u-bolts.
I have made an instructable for this machine: https://www.instructables.com/id/Low-Budget-CNC/
I have also made a complete 3D model in Fusion 360 so that people can take a closer look at the design. The 3D model is found in the instructable