At 3M's monthly equipment auction in August of 2001, I spotted what
appeared to be two identical 3-axis mills. While not unusual to find
these sorts of devices at the auctions, the fact that they weighed less
than a ton was. Although I could see that X and Y travels were
limited to only ~4", when I opened the cabinet back, I was greeted
by a welcome sight: 3 microstepping controllers! I submitted my bids
and thankfully was called to pick up the mills a few days later. A quick
look on the Net produced some interesting information: I found a
picture of this exact machine "used for fabrication of dental
The process of converting them to classroom use began by reverse
engineering the spindle control (since I was already quite familiar
with the control of "step and direction" stepper drives).
While I could have substituted a Dremel, it was pretty clear that the
spindles (two per mill) were high-quality, brushless DC devices. Slowly
(painfully tedious) I was able to discern the functions of necessary
leads in the 16-wire cable coming out of the spindle control board,
and utilize both on/off and speed control capabilities.
Having tested the spindle and three axis motion (with home and limit
switches), I soldered up two permanent
interface boards and modified the spindle orientation to a more
intuitive Z direction. After a trip to Home Depot for some polystyrene,
I started to have some fun...
My first trials involved milling out the Science Museum of Minnesota's
logo. Using a larger bit to do the roughing, and a 1/32" bit for
the detail. (pic coming)
The next step was to see whether I could bridge the 3D modeling and
animation software, Blender, to
these machines. Blender is powerful FREEWARE, which is taught to students
in the Learning Technologies Center at the SMM, in their animation classes.
Blender, while perhaps not the easiest package to use, is an obvious
choice for novices unwilling to shell out hundreds or thousands. The
idea: students create a 3D surface in Blender, then save the data in
a way that can allow a toolpath to be created, and fed to the mill--
virtual reality converted to real reality.
Unfortunately, Blender's export abilities did not match my requirements.
Fortunately, Blender is able to run Python
scripts. Unfamiliar with Python (and Blender) I hit Borders and bought
a couple books. They enabled me to write a simple
script that allows saving Blender meshes in an ordered fashion that
I can turn into toolpaths. The first "proof of concept" examples
involved mathematically "deformed" surfaces. And then, utilizing
Blender's texture mapping facilily, the sculpting of a surface using
the brightness of a bitmap. While not a true 3D rendering of my
daughter's face, when viewed under the right lighting, it appears
To further the capabilities of these mills, I contacted the makers
of Mastercam (CNC Software, Inc.).
After explaining our goals, they graciously offered to donate a copy
of their industry leading CAM software. With this sophisticated package,
we should be able explore far more complex toolpath options. Hopefully,
I will have examples in the near future...
A recent call from a neighbor friend who is a physicist, illustrates
the wonderfully unpredictable uses of DIY CNC: he creates highly specialized
spectrophotometric equipment (Mössbauer
Spec), and needed custom flexure plates (flat springs) to enable
a portion of his apparatus to function properly. Because of their small
size, this was a perfect job for the dental mill. He emailed the desired
geometry, and after setting up the toolpath, I did a test
pass. Then the real material (beryllium
copper). He sent over this pic of the prototype