NeoPixel Clip-On C9 Diffusers for Christmas Lights

Sometimes, good things go away – such as the frosted C9 bulbs. You know, the ones where the paint chips off. Yeah, those frosted C9 bulbs of Charlie Brown goodness.

Here's a proper C9 LED diffuser for the 12mm WS2811 NeoPixel addressable LEDs.

By proper, I mean the C9 diffuser is modeled after an actual C9 bulb. Because that's how proper is done.
AND it clips on! Consider that properer.

This is NOT About the Arduino, Code, or Power
You don't need to know Arduino, since you can buy a kit that includes everything but the 3D printed part (affiliate link straight to it).

If you do want to do your own custom Arduino implementation, here are my go-to resources for doing just that:

Adafruit has a great article on powering NeoPixels.
Adafruit also has a NeoPixel Überguide. Check it out.
Wanna Pseudo-Async? Adafruit wrote an article about that, too. I use their technique often, such as in my Smoking LED Candle Instructable.

This IS about creating the diffuser and learning a 3D printing technique
The world seriously needs to bring back the nostalgic C9 bulb, and this Instructable is to bring the frosted C9 look to the wonderful world of addressable LEDs such as NeoPixels.

Supplies

These C9 diffusers are designed to clip on to 12mm round NeoPixels / Addressable LEDs.

To get started quick, you only need 2 things:

LED kit
Filament

LEDS

You'll need a strand of LEDs. It's up to you whether you get a kit that includes everything, or a strand to wire up to your own Arduino contraption.

Option 1: Kits: (no need for Arduino)

Option 2: Strands Only: (requires an Arduino and custom power)

Adafruit - 4-wire WS2801 (5V, GND, Data, Clock)
Amazon - 3-wire WS2811 (5V, GND, DI)

WHITE FILAMENT - I have had great experiences with each of these spools of filament, and have found Hatchbox, Overture, and Priline to be good all-around go-to brands (not affiliated with any of those companies):

For this Instructable, I'll be using PLA. I've used PLA and PETG for these C9 diffusers with great results, and imagine ABS and TPU would be nice as well (assuming you know how to print with those). All filaments listed are actual brands of filament I've used (and found to be consistent spool-to-spool) in the mentioned plastics.

Don't have a 3D printer? I highly recommend the Creality Ender 3. It's inexpensive and well-regarded in the 3D printing world. I have two of them and love them!

*Amazon links are affiliate links. Sometimes, the best way to say "thanks" is to buy yourself something nice through one of my links :D

Step 1: Download the C9 STL

Download the C9 Diffuser STL model from Thingiverse here: https://www.thingiverse.com/thing:3331268

That's pretty much all there is to say about this step.

Step 2: Slice It (things to Consider)

The goal is to get a UNIFORM, frosted look. A uniform glow. Minimal layer lines. No Z-Seam.

I'll be using Cura slicer. Download it for free here: https://ultimaker.com/software/ultimaker-cura

The Challenge:

Typical 3D print settings leave layer lines & z-seams. Luminescence through plastic emphasizes those things in a bad way.

You've gotta do something fancy, and I recommend solving this problem (and I'll show you how) by utilizing either:

Spiralize (vase) mode, or
Fuzzy Skin

Pros/Cons of each:

Spiralize Mode

Pros:

Avoids Z-seams by continuously moving upward in one single spiral movement

Cons:

Can still see visible layer lines - though they are minimized
Can only print 1 bulb at a time.

Fuzzy Mode

Fuzzy mode introduces jitters to your print, giving it a "fuzzy" sort of surface. This does a wonderful job of scattering light and hiding layers and seams.

Pros:

Jitters reduce layer lines by introducing non-uniformity at a granular level to obscure the layer lines.
Jitters hide the z-seam, allowing you to print multiples.
Jitters bounce light around in more directions to give the bulb's light a more "full" look

Cons:

May involve fine-tuning your fuzzy settings for proper fit at the base, but I'll share the settings that I like to hopefully save you the hassle.

Sure, you could do both fuzzy & spiralize, but you'll be limited to 1 bulb at a time, and I don't think it's worth it.

Step 3: Slicing With Spiralize Mode (Vase Mode)

Spiralize mode works well for 1 bulb at a time. Here are the settings to set:

Check the boxes "Spiralize Outer Contour" and "Smooth Spiralized Contours."
Specify 2mm of "bottom" layers. This will make sure the bottomtabs print non-spiralized. --important

But, for each bulb, you'll have to remove the print, then re-start the job for the next bulb. That could get annoying if you want several dozen diffusers. The next step solves this problem.

Step 4: Slicing With Fuzzy Mode (recommended)

I print an entire bed of these C9 diffusers overnight using the "Fuzzy" mode in Cura. Cura's fuzzy mode hides the seams exceptionally well. (or so it...seams.)

Fuzzy Wuzzy Wuz A Cura Setting:
You may need to adjust your fuzzy settings to achieve the effect you like. Here are the settings to get the effect I like w/ a 0.4 nozzle:

Fuzzy Skin: CHECK
Fuzzy Skin Thickness: 0.15mm
Fuzzy Skin Density: 1.25mm
Fuzzy Skin Point Distance: 0.8mm

NOTE: Fuzzy is an "Experimental" mode, and Ultimaker recently introduced a couple new settings. If you find settings that work better based on your version of Cura (mine is 4.5), leave a note in the comments, along with your Cura version # so others can see!

Step 5: Slicing: Other Tips & Settings

The previous steps only covered settings specific to Spiralize & Fuzzy modes. Here are a few other settings I recommend trying that apply to both Spiralize & Fuzzy.

Layer height: 0.2mm
Nozzle width: 0.4mm
Infill: Doesn't matter, it's a hollow model and there shouldn't be any infill.

For temperature & speeds, check your filament's recommendations.