To easily hold stuff in place on the MPCNC, I used OpenSCAD to script it to drill a grid of 9mm holes in the bed, then I installed 1/4-20 threaded inserts into them. This lets me tighten down simple 3d-printed hold downs with normal 2″ bolts.
The pen holder was actually somewhat complex. The pen I wanted to use was a Bic 4-color, and its barrel has a very slight taper to it, so I had to model it fairly precisely and it took two prints to get the dimensions right. Now that it’s done, though, I can get really nice, repeatable drawings. I’m thinking of developing an algorithm to convert images into combinations of the pen’s four colors and emit gcode to approximate color printing. It will be ugly due to color theory (there’s a reason printers use cyan/magenta/yellow/black), but it might look neat.
The MPCNC with my rudimentary pen holder was able to draw this. I need to add some kind of spring downforce on the pen to deal with small differences in depth (which is why the lower left is faded). That should also help with pen accuracy, because on the high parts it’s grinding the pen too hard against the page and its getting stuck. I also need to turn up my overlap to get it to solid fill better.
On Thingiverse I’ve posted a model and schematic for a relay-switched outlet box. This will let you switch an outlet on/off with an Arduino pin. That’s nothing new, but it’s a box that puts all the components together in a neat and safe package.
The model holds a U.S. power outlet, IEC C14 power inlet (for use with common PC power cables), a cheap arduino-compatible 5V relay module, and a small Dupont connector for the control relay module’s inputs. The wiring diagram below shows how to make one outlet switched with the other being always on.
The intent of this model is provide a switched outlet for my Mostly Printed CNC machine (MPCNC). It’s designed to be narrow so it could mount on the side of the machine to (a) provide always-on power to the power supply and (b) provide switched power to the AC spindle motor. That said, this model is a general-purpose switched outlet, so you could use it for any automation of AC power you need.
See photographs below for assembly directions. Notes:
- The faceplate is a standard one cut down to fit the width of the box; you could modify something like this if you had to print one.
- Relay modules tend to vary in size — move the screw posts in the model if needed.
- The relay control wire is just three double-female dupont jumper wires taped together and hot glued in place.
WARNING: This switches high voltage! If you are unsure how it works or how to build it, consult someone with electrical experience before proceeding! This isn’t hard to build, but it can kill you if you touch the guts when it’s live, and it can start a fire if wired wrong or with insufficient gauge wire (18AWG to probably not die, 14AWG to meet code).
I tried a test run of the Optimal Fabrication Test Model (it’s dickbutt…we talked about this).
Results were…mixed. It started out strong by making key outline portions, so I left the room. I came back when I heard the spindle inexplicably struggling from downstairs. I come back to find the spindle has sunk all the way into the foam, and the nut that mounts the endmill to the tool has itself ground a sizable trench through the foam. Bits of foam are everywhere.
It turns out two separate failures happened. First, the Z coupler came loose…that’s my fault, as the plans called for nylon locknuts, but I couldn’t find any locally, so I used plain hex nuts, so the screws tightening it vibrated loose. Locknuts: ordered.
Second, there was a flaky connection on the X-axis, which is why it’s a vertical trench instead of a vaguely dickbutt-shaped trench. Apparently the wire I used doesn’t like to crimp well in Dupont connectors, so I crunched them all harder and added a bit of solder to be sure.
I 3D printed a pen holder to attach to the tool, so I can do ink-based tests while I work out the kinks. I did a dickbutt print on the same crappy foam, offsetting it a bit upward. The result is surprisingly good, given that the foam is nowhere near level, and I used the same program that assumes a 1/8″ endmill. Look at the solid ink on those eyes…nice!
I strapped an incredibly crappy Harbor Freight Cutoff Tool to the MPCNC (related posts) thanks to this mount, and I was actually able to mill something! It worked! I crudly cut the hand-drawn letters “CNC” into the foam that the tool was packed in!
Now I just need to connect a power relay to automate the tool, add end-stops, learn to use the CNC software, learn to use good design software, possibly get better client software than Repetier Host, and add some kind of clamping mechanism to the table surface.
If you like clumsily drawn squares, you will like this video.
One difference from the stock guide is that I’ve mounted mine on a metal table with folding legs to make it portable.
Pics and videos: