For my upcoming R2-D2 robot I needed a dome. More than that, a intricately detailed dome. I immediately knew my 3 axis CNC wouldn’t cut the mustard and neither would my 3D printer (footprint too small). I have always wanted to make a 5 axis CNC with rotary axes… Let’s go.
My 4 axis CNC is more like a 5 axis CNC in the fact that it has two rotary axes, however it only has two Cartesian axes (X and Z). There’s no Y axis because I simply didn’t need one to cut a dome. Adding a Y axis would’ve added a great deal of complexity and cost (moving gantry, larger frame, more expensive and stronger parts needed etc).
I designed this CNC with only light duty machining in mind. Primarily it’ll be machining wood like balsa or hollow plastic with a dremel for a spindle. Additionally the frame is fairly lacking in the strength department but I ain’t gonna be machining metals any time soon on there!
Starting with the X axis; A NEMA 17 stepper motor drives the GT2 belt that moves the head left and right. The stepper motor is mounted to an adjustable mount so I can easily tension the belt. On the opposite side from the stepper motor are two skate board bearings (8x22x7mm) mounted on an M8 bolt which acts as idler pulley.
The Z axis is also powered with a NEMA 17 stepper motor, attached via a coupling to the 8mm diameter leadscrew. The screw has a fair bit of wobble and whip to it so I may need to upgrade it.
The B axis is powered by a NEMA 17 stepper motor, in fact (spoiler) the whole CNC uses NEMA 17’s. The motor has a 3.75 reduction (16T pulley on the stepper to a 60T pulley on the spindle mount). The belt is the classic GT2 as seen on every 3D printer ever. The stepper motor is attached via long M3 standoffs and it can be moved up and down to tension the belt.
Finally the C axis is the rotary table. The work piece will be mounted directly to this table. It’s the exact same mechanism as the B axis; a 3.75 reduction with 16T and 60T pulleys. The rotary table is mounted to a 200mm lazy susan bearing.
Here’s the electronics. I’ve temporarily thrown them in to an enclosure with a 80mm fan to keep the stepper motor drivers cool. I’m using a 12V 10A power supply to power the RAMPS 1.4 board. I had to modify the grbl (CNC controller software) source code to run on the RAMPS board as it doesn’t natively support it. I had to do quite a hack job to disable a lot of safety features to get it all running! More work needed there for sure.
Just some final quick bits of info:
- Predominately PVC is the main construction material. The grey plastic is solid PVC, white plastic is foam PVC – wouldn’t recommend this stuff, it’s too soft and I’ll be upgrading it in the future.
- The black metal beams are OpenBeam 15x15mm aluminium extrusions.
- Hardware design isn’t done, I’ll yet be adding some more parts to strength it up.
That’s it for now folks! Next post I’ll detail the custom software I’ve made to run this beast.