outside profile pass. I didn’t have an end mill long enough
to make it through the whole slab of 2” foam, so on my
outside profile, I cut it through as far as I could, then hand
cut the rest of the way through with a knife.
Now that you have your tool paths, you export them
as g-code through the appropriate post-processor, and
then carry that g-code over to the CNC machine on a
USB thumb drive and load it into the control software.
Our machines at Probotix run the open source software
I was cutting this particular part on the Probotix
FireBall Comet™ CNC router that has a 25” x 25” work
envelope (Figure 3). My foam slab was 18” x 24”, so I had
to be careful that I mounted it to the table inside of the
travel envelope of the machine. Double-sided 3M tape that
has the green argyle backing is what I like to use for
mounting stock to my table. Use a generous amount so
the stock doesn’t come loose in the middle of the job.
Once the stock is mounted, install the tool into the
spindle and then jog the tool over to the corner that you
chose for the origin in the CAM software. Then, you will
“touch off” each axis. What you are doing is telling the
control software that you are now sitting at the starting
point of each axis, or X0 Y0 Z0.
Give yourself a sanity check and look at the 3D tool
path on the display. You want to make sure that the tool
path appears where you think it should within the work
envelope bounding box on the screen (Figure 4). Then, hit
the start button, sit back, and watch (Figure 5).
About 30 minutes later, you will have the basic
tombstone carved out. So, pry it off the table and remove
the double-sided tape. Figure 6 shows what it looked
like after I cut off the outside scrap. Pretty cool already,
September 2014 83
LinuxCNC showing tool paths.
FIGURE 3. ProbotixFireball
Comet CNC Router.