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I've recently bought this crystal clear filament from Fillamentum.

I've tested it out by printing a small icicle and I was blown away by how great it looked!

That got me thinking; could I scale it up, print a bunch of them and stick an LED inside to hang them as Christmas decorations?

The final result!

I've searched on Thingiverse for icicles and this is the design I like the most, so that's what I'll start with.

Import the model into Fusion360. I'll replace the bottom part, so I can cut it away to get an even surface. The easiest way for me is to simply create a cube where I want to cut the other model and then use the Combine function with the Cut operation.

I'll be using individual LEDs from this strip, one for each icicle. It's nothing special, just the cheapest one I found on AliExpress.

I could design a simple lid for the bottom and just glue it in place, but that's lazy and you can't replace the LEDs if they ever fail.

Instead, I'll modify this screw and nut model from Thingiverse. If I place the LED on top of the screw, I can have easy access to it.

Nut attached to the base of the icicle.

The screw itself is too large, we only need a small surface, and I'll shorten it a little as well, just enough to reach the inside. Everything was done using the cut operation again.

I've printed the screw part of the icicle normally and the icicle itself was done in vase mode. Not all slicers will let you do this, so you can print the entire icicle normally. In that case, your printer needs to be calibrated really well or you will see artefacts on the wall. Check out my complete printer calibration video if you need help with that.

Of course, I need to run the cables to the LED somehow.

I could simply make a hole in the middle, but I plan on hanging the icicles outside. Having a hole at the top would let all the rain inside, which probably isn't the best idea.

Instead, I've designed a channel with an opening at the side. It's even better if I curve it upwards at the opening. This should prevent any water from coming in.

Let's finish one test icicle and see how it looks.

Simply screw everything together.
LED works as well.

Seems to fit, but talk is cheap. Let's test it to see if it actually works. I've poured 2L of water over it and the light stayed on the entire time. I've quickly unscrewed it afterwards and found no traces of water inside.

This reminds me of another issue. Because of the cold weather, condensation might build inside over time. It's a good idea to let it drip out somehow. A small hole at the bottom should help with that.

As a final touch, I want to be able to hang the icicles so there has to be a hook somewhere. Going back to Thingiverse, I found this hook that I really like. There's even a strong version with extra thickness.

This might look ok at first, but it's not. It's impossible to print it without using a lot of supports, and I don't like that.

Let's consider a different approach. We can put the hook on top of a smaller screw and then easily to attach it to the base of the icicle. Because the bottom of the screw is flat, there's no need for any supports.

And you're free to replace the hook if it ever breaks or if you come up with a better design, such as having a ring instead of a hook.

No supports are needed with the improved design.

Here's how I'll connect everything together. I'll use one main cable and then connect each icicle to it.

Here are a few steps of the build process.

A bit of solder...
... and heat shrink tubing should hold everything firmly.

Finally, let's connect everything to a power supply. Be sure to use the correct voltage for whatever your LEDs require. I'm using 5 volt LEDs, so I can simply hook them to USB power supply.

Be very careful with this step. You should never add more LEDs than half of what your power supply can handle. Cheap power supplies are notoriously over-rated in the specifications, but they can barely manage half of that in real life.

My LED uses up about 20mA and the power supply is rated for 1A. Assuming a safety factor of only using up half the supply, that leaves me with 0.5A, which is enough for about 20 LEDs.

As a final safety measure, I'll add a 1A fuse next to the power supply as well. Most power supplies should be able to handle short circuits, but it never hurts to add an extra fuse just to be safe.

Everything wired together and ready to be used.

I'm happy with the results, but next year, I'll make a better version with more LEDs inside and a cascading effect.