Ever since my brother was a wee boy he wanted a CNC machine. While I was climbing trees, playing tag, and goofing around, he was tinkering with electronics and salvaging parts from old scanners. In fact, he wrote an instructable on how to build a stepper controller from recycled parts 7 years ago when he was just a kid (side note, that thing got over 300 000 hits!). Needless to say, a CNC machine was his childhood dream.
Over the years he made a few attempts, which were impressive given the materials he used and the fact that he was just a kid working on it by himself. However, they weren't exactly functional. Fast forward 5 or 6 years and I decide that this CNC stuff might actually be pretty cool. So we teamed up and built a CNC machine out of MDF. This machine moved and made a few cuts in foam, but it was admittedly pretty mediocre.
At this point we said "forget it" and did what anyone else would do; we built a 3D printer instead. And... The 3D printer (a Reprap Rostock) actually worked really well!
Jump to the next year and we've gotten a lot better at building things, I know how to use 3D modelling software, and we're ready to give this CNC thing another go.
This time we opted to use metal and plastic (no MDF except for the bed). The main frame is constructed from aluminum angle, and all of the motor mounts and rod guides are 3D printed with PLA. The linear rail system consists of 3D printed PLA bushings sliding on 1/2" drill rod. This is super cheap and works great in this setting.
These older photos give a clear view of the frame design. The spindle you see in the photos is just a dc motor with a collet attachment. These spindles are useless for anything other than light engraving. A rotary tool is a much better choice.
In the final assembly corner joint reinforcements are installed:
We are running large Nema 17 steppers on the X and Y axes with a 3.75:1 belt reduction.
The Z axis has a smaller Nema 17 stepper with a multi-start 8mm pitch lead screw. The X and Y axes are belt driven with 6mm GT2 belt. I'm quite happy with this design. The 3D printed parts provide accurate alignment and ease of construction, while the aluminum angle and drill rod provide rigidity and strength. Hannah Montana isn't the only one getting the best of both worlds.
The machine has a roughly 10"x10"x2" cutting area (x,y,z). A 2" Z axis doesn't seem like much, but when you're using a spindle with a 1/8" collet (a dremel in our case), you aren't going to find many bits that can cut much deeper than this anyway.
Traditional DIY CNC skeptics would probably suggest that unsupported rods, printed bushings, and printed brackets and fittings would lead to a uselessly flimsy CNC machine, but in fact the machine is more than sturdy enough. When it comes down to it, a machine is only as good as its weakest component. In our case the dremel or the steppers will stall out long before the rigidity of the frame becomes an issue. This machine won't be cutting metal or hogging through 1/2" of wood with a large cutter, but it wasn't designed for that. It works perfectly fine for milling circuit boards and cutting wood with a reasonable depth of cut.
The enclosure is constructed from pine and plywood with a sliding plexiglass door on the front and plexiglass windows on the sides. The enclosure works great and I can't imagine using the machine without it (sawdust everywhere!). We have a small shop vac hooked up to the head of the machine to keep the dust at bay while the machine is cutting.
Every CNC machine needs a big red stop button.
As for the electronics, we are using an Arduino mega with a ramps board. It is running a version of GRBL. We are currently controlling the machine with BCNC on the computer.
Now what you've all been waiting for... A video of the machine working!
As you can see, the cuts are very clean and precise.
I'm sure we'll make some more improvements over time (first up is a proper vacuum attachment), but I think it's safe to call this machine a success. We've named it the Rift because it fiercely (and very slowly), tears great divides into wood!
*Update: The files for the 3D printed parts are now available for download.