Art Deco Lightswitch Cover and Multi-color Prints

This started off as a project to make a lightswitch cover that was interesting and unique. We've been looking at buying a house, and when I mentioned that maybe doing custom ones would be fun — yes.

For this project, I used Blender 2.8 and older developer version Cura (2.x, but is able to run on an ancient OSX desktop). The file can be found here - https://www.thingiverse.com/thing:3907742

Lightswitch Cover Design & the Foray into Art Deco

It would have been an easier start if I had just remixed someone else's lightswitch cover as a base. In this case, I decided to do everything from scratch. Starting with digital calipers, I decided the plate would be 114 mm tall and 71 mm wide. I measured the slot and the holes, using blocks and cylinders to punch holes in the plate. (The cylinder was wider at the top, to represent the tapered screw that lightswitches use.)

I did some beveling on the top and the underside to get a rounded feel for the cover — one of the useful techniques when using control-B to bevel, or Edge>Bevel Edges is using "M" to change the mode...I clicked M several times to get to "percent", which turned out really well. I've done some basic bevels in the past, but this is the first time I experimented with every combination of options before settling on the one true way.

Added some cylinders on the bottom for more screw support. The bevel on the actual bottom came from inset, followed by moving the portion up past the top's bevels, then applying bevel/percentage to the rectangle that had moved up. Tricky.

Before printing this cover, I downloaded someone else's plate from thingiverse, compared the slots and holes...pretty close. I did end up moving the screw holes .3mm closer to the center, but not bad. Printing it, I realized I had not put enough taper space into the plate for the screws. Ah well.

With the basic object shape out of the way, we get into an introduction of "art deco". As I'm not a designer, I went to Google Images, and searched for "art deco pattern". After browsing a ton of images and styles, I decided on one that was relatively simple. (Showing my beta version to an actual designer type person, he asked if I was a designer, and explained that I got the style right - basically a simple image that repeats...that's what I got out of his comments at least.)

The goal was an image that would merge together with itself. Didn't like my design at first, but it looks good printed. 

I created the basic image, sized it up to 15 mm, then used the array modifier for the relative offset y-axis at "1.25", 20 times. I created a second array modifier, .65 for x-axis, .025 y-axis. This wasn't science, it was trial and error to get a feel for what it would look like.

Next was...ugly. I clearly need to learn better habits on how to merge the art deco design onto an object.  It *eventually* worked. I needed to use a lot of the 3D Print Toolbox plugin to look for non-manifold edges. There were over 300, and I did too much manual fixes and partially manual fixes to get down to 0.

Multi-color Prints & How to Pause in Mid-print

A friend asked me how hard it was to imbed something within a print. Specifically, adding a metal nut into a knob as it prints. Sure, it could be done, but I didn't know how or had a project that needed me to stop in mid-print...until NOW.

The idea was to print the art deco image in a different color - imagine a white plate with a series of black stamps. There's a plugin that comes native to Cura, found under Extensions>Post-Processing>Modify G-Code>Add a script>"Pause at height". From Blender, I recognized I needed about 5mm of white before switching over to black. Loading the cover, clicking on the View, Layers...it looked like I needed to switch over at layer 21, at a .24 mm layer height. The only number I had to change for the input was the Pause Height to 5.04mm (arrived at by multiplying 21 * .24).

[edit: I came back a year later to update some of this.]

If you have a different initial layer height, make sure that is figured as layer 1. (For example, a .3mm layer height, and 20 layers at .24...5.10mm.) You can also resume the print from your Octoprint browser window, if you don't have Cura open.

I'm trying out "Extrude Amount" with a new print - it's supposed to extrude filament after you resume. You'll still need to be quick, to clean off that extruded filament before it starts printing on the model.

[edit end. November 29th, 2020.]

You can add multiple pause at heights, for multiple color changes from highest (top) to lowest (bottom).

And I started the print. At layer 21, the printer paused and sent the printer head to the far right corner, and elevated on the z-axis slightly. The Cura software was still open, and registered as "Paused". I opened up the tensioner on the feeder, slowly pulled the white filament out, slowly pushed the black filament through. Caution! Try hard not to move the printer head - if it loses where it is, it won't be aligned when it starts with the new color. (If you look closely, you can see white at the top of each black circle, where I bumped it slightly when using the feeder gear to push it through. The second time, I just pushed it through manually, no gear.)

Going back to the Cura software, it was still paused. Click the resume button, and it goes back to printing. Sadly, my bed temperature was low for PETG (and the room was drafty), so you can see how the corners were pulling up. That's fine for experiments, but wouldn't be good for the final result.

Action shot, printing the black as layer 21

I also found that the cover no longer printed correctly. The screw holes and switch slot in the cover filled on some of the layers! Sure enough, back in Cura in View Layers, I noticed that it filled up. Spending some time in internet searches, the solution that I found suggested in the "Mesh Fixes" options, to DISABLE "Union Overlapping Volumes". That brought back the holes and slot that should have been there in the first place.

The screw holes are white, the switch was black...clearly neither were holes anymore This version had beveled edges on the outside, which meant they ended lower than 5.04 mm (still the white filament).

Having done that, I went back to printing the white/teal PETG to get this final product. (230 degrees nozzle, 70 degree plate, .24mm layer height, .5mm nozzle.) Polymaker's Polylite PETG, 2.85mm.

Ta-da!