This was my first attempt on designing and building a 3D Printed CNC Machine that is powered by Nema17 Stepper Motors and 8mm lead screws and controlled by a cheap Arduino based CNC controller. 

The moving components are based on 25mm hardened steel rods and linear ball bearings. I also tried normal non hardened metal tubes before but the ball bearings just destroyed them.

Beside the printed parts you would need a few extra things to build this. Please keep in mind that I never planned to create a full DIY guide to build this thing. I just made this out of curiosity and it worked pretty good. This being said, you might need to tweak a bit here and there, maybe some of the components I used are slightly different than the ones you buy and you need to make it fit.

I printed the 3D parts in PLA Plus with 100% infill to make them as strong as possible (you need a few rolls of that). Beside that you need the following things to build the machine:

Rods:

• 4x 600mm Steel Rods (25mm in diameter)
• 2x 800mm Steel Rods (25mm in diameter)
• 2x 205mm Steel Rods (12mm in diameter)

Bearings:

• 8x 25mm Linear Ball Bearings
• 4x 12mm Linear Ball Bearings
• 6x 608-2RS Skateboard Bearings

Motors:

• 4x Nema17 - I went for 65Ncm(92oz.in) holding torque but if you find stronger ones perfect.
• 4x 8mm couplers to connect motors and lead screws
• 3x lead screws 1m (you can easily cut them to length and should have enough for X/Y/Z Axis

Electronics (I don't really want to go dow this route but there are great Videos on Youtube on how to build a GRBL CNC Controller based on an Arduino)

• Arduino Uno (or equivalent)
• CNC Shild V3
• 3 Stepper Drivers (don't go for the cheapest ones here)
• Enough Cable to extend all the Motor wires
• Power Supply
• 4x Limit Switches (Link)

Others:

• 1x 30x40mm L-Profile 820mm long
• 3x 30mm Drag Chain (can#t remember what I bought or how long but I bought 3 packages and didn't use all of each package)
• Board to mount it on
• AMB 1050 Router with manual speed control

Cost:

With all the electrical components, Router, Rods, Bearings and Filament, etc. I ended up spending somewhere around 600-700 Euros. But if you buy the components smarter and can wait for them to be delivered in a few weeks, you can get this all done cheaper.

WARNING: As mentioned above I created thi project purely for fun and mainly for myself, I can't offer support or troubleshooting or even a guarantee that you'll be successful. If you feel like you need a lot of help figuring out how this all goes together and how to program it, it is probably not a project for you. It would be a shame to make all the investment to have a bunch of stuff that won't work later on. The parts I used are also not the cheapest ones and financially it is probably a bad idea to even build this yourself instead of just buying a Machine from Sainsmart or other vendors.  

This being said, I still thought there might be others out there that want to give it a try or just get some inspiration.