Background story: I want to build a largish MPCNC in my outdoors shop, a rectangular one that needs to conform to the available space, needs to cut 60x60 cm parts out of HDF/MDF (or whatever the really strong wooden laminate thing is called) and needs to cut small parts out of aluminium. Right now here in Romania we’ve got temperatures in the -10 to -5 Celsius range (Google says that’s 14 to 23 F) and I’ve got no heating out there, so that will only happen when Spring comes.
Since I can’t have my big machine right now, I decided to build a small machine that would allow me to learn CAM and work on software. I ended up building a machine that sits on a 450mm x 500mm table using 12 mm diameter piping!
I wanted a machine small enough to keep indoors near my desk. I decided to build one using stuff I can buy locally. Went to the hardware store, looked around for metal piping, found absolutely nothing useful, so I bought some length of 12mm outer diameter stainless steel piping. You heard that right, 12mm… Next I went to a different hardware store and asked for bearings: I requested bearings with outer diameter in the range of 15-20mm, whatever size they have that’s both cheap and in stock. I got 60 bearings with an outer diameter of 19mm and an inner diameter of 6 mm. Then I spent an awful amount of time redrawing every singe part in Fusion 360, because you can’t scale STL’s from 23.5mm down to 12mm and end up with useful parts.
Now let me tell you what I’ve learned while redrawing those parts: Ryan is a genius. This machine is fantastic and it all comes down to geometry. It’s strength and rigidity comes from the way parts brace each other, not from the might strength of the PLA plastic. This machine is rigid despite the flex in the rails and the variability in printed parts.
Next I bought a few kilograms of nuts and bolts, because I was too lazy to include all the hardware in the CAD design. I obviously made mistakes, occasionally needing screws shorter or longer then the ones I already bought. I also had to cut chamfers in some of the printed parts in order to use sunken scrwes. I could have re-printed those parts, but decided it’s not worth the lost time and plastic.
I designed the thing to take NEMA 14 motors - in theme with the “small” concept. Then I modified the parts to use NEMA 17 OR NEMA 14 parts (I have two sets of holes for the screws, with the NEMA 14 set rotated at 45 degrees to maintain some separation). In the end I installed NEMA 17 motors, the ones I bought for the future large machine, becuase my NEMA 14 motors have not arrived. I’ve ordered them 1 month ago…
I uses a RAMPS 1.4 card with 5 stepper drivers using Marlin’s X/Y_DUAL_STEPPER_DRIVERS; fixed a bug in Marlin that prevented the 2nd “X” stepper to enable. Only noticed this because I was playing with the firmware with no belts on, I had cable-ties tied to the steppers to make motion obvious.
For the spindle I used the mighty-powerful 30W (yup, thirty watt) Proxxon rotary tool. I made a mistake with this tool: it’s marketed as a 12V tool, I thought I could run it from the same power supply as the rest of the “toy”. Unfortunately it’s not exactly 12V and it’s definitely not 12V DC. I had to buy the corresponding power supply. As I understood it’s an unrectified 12V transformer that allowed simple/cheap RPM control. Not that it’s RPM control would be of much use: it simply doesn’t have enough power to spin fast when it hits wood. It did have one very good thing going for it: I learned to control depth-of-cut in Fusion 360’s CAM module. That is, after accidentally plunging the bit 1mm deep into the MDF spoil board: the bit stopped spinning then it broke!
As for the future of this machine, I’m now printing a tool support for a different spindle: a brushless 480W Chinese thingy. This should allow me to use larger bits or take deeper cuts. With the 30W Proxxon I was taking 0,5mm deep cuts and by the sound of it it was too much. I’ll play with the larger spindle until I build the larger machine, then I’ll reinstall the Proxxon and repurpose the small machine for cutting PCB’s.
On the software front I’m now working on a Marlin firmware feature for Jogging the toolhead. Moving the toolhead with G0 commands is painful and moving the toolhead by hand means no endstops and no help with tool changes. (moving the toolhead with the LCD pannel is equivalent to using G0 commands).
And finally, have a nice day and enjoy the pictures. I’ve got a few videos of the thing cutting the Batman/Victor sign, I’ll have to post them to Youtube in order to share them here.