Converting a Proxxon MF-70 Mill to CNC

I recently converted my mf-70 to cnc control, and I’ve decided to write about it because it’s surprisingly easy, and makes an awesome tool. Seen above is the completed mill, next to a SOIC-20 breakout board I milled with it.

I’m going to divide this post into:

1) Mechanics: Basically just coupling stepper motors to the axes. Also, replacing the spindle motor with a brushless motor (optional).

2) Electronics: usb->rs232->gcode->stepper commands (Basically reprap electronics).

3) Software: PCB layout -> gcode.

 

1) I decided to use NEMA23 steppers to control the 3 axes, since I had some lying around. They have a LOT of torque, and are small enough to fit easily. Initially, I used some 3d printed couplers (http://www.thingiverse.com/thing:9622) to attach the motors to the threaded rods. They had a fair bit of slop, but the real aim was to manage to cnc mill some proper oldham couplers:

Oldham couplings have the really nice property that they tolerate axial misalignment quite happily – in my case I’m using 32mm steel rod for the coupling, and they tolerate 5-10mm misalignment well.  Milling instructions are in the previous post on this blog.

Annoyingly, I managed to burn out my spindle motor within hours of use (I was milling steel at much too fast a feedrate so the motor stalled). I was initially panicked, but then realised I had a spare brushless motor than might just do the job. I ended up using a TURNIGY plush 25Amp ESC with a TURNIGY 2217 860kv 22A outrunner, and coupling to the spindle with a small 3d printed part I made (http://www.thingiverse.com/thing:115759). The motor was loosely secured with cable ties. I needed some control that would output servo commands to control the ESC, so I used the schematic at: 556 Based Servo Exerciser . The fan sitting on top is to cool down the motor (the motors can overheat, since they’re really made to be coupled to a propeller in an rc model).

2) I had a bunch of spare parts lying around from previous 3d printer projects, so I mushed some together to get some free electronics:

1x sanguino board
2x stepper motor driver v1.2 (http://reprap.org/wiki/Stepper_Motor_Driver_1.2)
1x  DRV20/S (http://www.diycnc.co.uk/html/drv20_s.html)

I use marlin firmware (https://github.com/ErikZalm/Marlin), and the stepper drivers are easy to attach (step/dir/enable). You can use any stepper drivers and electronics that work with Marlin/grbl/whatever. The drivers get pretty hot, so they’re housed in a wooden box with fans at each end.

3) I use eagle with pcb2gcode to generate the gcode. You just need to generate the board layout with eagle, then use the CAM processor with (http://www.sparkfun.com/tutorial/BeginningEmbedded/9-EaglePCBs/sfe-gerb274x.cam)

Then, you just need a pcb2gcode millproject file (for arcane reasons, pcb2gcode expects a file called milproject in the current directory). I use:

# this is an example config file for pcb2gcode. 
# place this in the same directory as your gerber files to save typing metric=1 # You may want to uncomment and change those in local project file 
front=untitled.GTL
#back=diode_tester-B_Cu.gbl
#drill=diode_tester.drl 

# parameters for isolation routing / engraving / etching zwork=10 zsafe=12
zchange=15
mill-feed=100
mill-speed=30000
drill-front=1 

# drilling parameters
zdrill=-2
drill-feed=300
drill-speed=20000 

# generate voronoi regions
offset=100
dpi=1000

You’ll need the metric version of pcb2gcode at: https://github.com/festlv/pcb2gcode-metric

Then you just need to modify millproject to contain the exact file that you want to be milled, then you can just run ./pcb2gcode in the directory containing millproject and your gerber files, which will give you a .ngc file. You can then push this to the mill with something like pronterface (https://github.com/kliment/Printrun).

In order to get everything lined up correctly, I use the following steps:

I tell the FW that the axes locations are at some arbitrary large number (G92 X100; G92 Y100; G92 Z100)

I use pronterface to jog the axes until x and y are where I want 0,0 to be.

I tell the FW that it is at 0,0 (G92 X0; G92 Y0)

I move the Z axes down until the tip is touching the copper (I will in future automate this with a probe).

I then tell the FW that the Z axis is at 10mm + cut depth (say for example G92 Z10.2)

I hit start.

2 thoughts on “Converting a Proxxon MF-70 Mill to CNC

  1. Pingback: Converting a Mill to CNC

  2. Pingback: Converting a Mill to CNC | Maker of Meta

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