When I first got into CNC milling using the Othermill, one of my first project ideas was to try engraving on the surface of 3D prints to make details that otherwise wouldn’t look extravagant using just a 3D printer.
The first considerations where, can the object fit on the bed? Is the object thin enough for the clearance of the tool head? And, what bit should I use? After designing several PiGRRL Zero cases, there was plenty of spares to experiment with, so I decided to use that since it didn’t matter if things didn’t turn out right.
A simple title across the top of the case, above the PiTFT display would be an easy test. I drew up a simple graphic in Adobe Illustrator and exported it as an SVG.
Setting up the material profile in the Otherplan software was easy as inputing the dimensions using the HDPE material preset as a starting point.
Importing the SVG graphic was easy too, but here’s where my first issue arose. How do I precisely place the graphic so it’s in the right spot? I could take a few measurements and input them but I think it’s easier if I had a visual reference of the PiGRRL case in Otherplan. Like, a 1-to-1 scale SVG of the case.
To keep things simple and easy, I used TinkerCAD to export an SVG of the PiGRRL Zero case (just the face). That way, I could reference the PiGRRL outlines and easily position the title SVG on top.
Alternatively, I could’ve processed some GCODE using the CAM tools in Autodesk Fusion 360, but the SVG method reduces setup time and simplifies the tool settings. The Otherplan software does a fine job of handling all of the settings when choosing the material profiles and tool bit.
So with everything setup in software, all I had to do was try to square up the PiGRRL case onto the spoiler plate as good I could. Using double-sided Scotch tape, I secured the bottom half of the case to the spoiler plate, and simply snapped the top half on top.
The first milling attempt was on PLA/PHA material. It turned it pretty decent but there was noticeable dust in the etching. Using a vacuum and air dust can didn’t remove the dust. It seems like the chip (or dust) during milling gets stuck to the edges and surfaces (most likely due to the heat and low melting point of the plastic). So, a needle, hobby knife or anything pokey can be used to scrape off this dust. I didn’t spent too much time here, but I think if I spent more time cleaning it up, the engraving would have came out nicer.
The second test was done on a regular PLA print. The dust seemed to be more prominent. Perhaps because of the pigment of the plastic? Or maybe the the PLA/PHA bend is softer and less brittle than regular PLA. I’m not entirely sure.
I have yet to test ABS plastics or exotic composites, but my guess is they would be similar. There’s a bit of post-process / finishing involved, but I think the results can be pretty nice. Certainly higher quality of details than a 3D printer. I’ve done a few of these type of things on other projects and found details come out better going up on the z-axis as opposed to flat on a surface (especially on the first layer!!).
If you’re interested in giving this a shot, by all means give it a go.