Water-tight Prints

There are loads of applications for Ninjaflex and other flexible filaments which require holding a liquid. So let’s talk a little bit about some of those applications and how to get your 3D printer to achieve a water-tight print. Generally, the two categories are containers and molds. Containers are essentially bowls. Molds are way more complicated. We’ll start with containers.

Basic ice cube tray – Thingiverse link

Your basic ice cube tray is a container. Gravity holds the water in place. As long as your floor and walls are water-tight, then you are good to go making ice, jello, popsicles, candy, etc. But how do you make the walls water-tight? Ninjaflex is pretty conducive to fully-dense parts, but your extrusion settings need to be really dialed in. It is possible to do this with a single trace width (0.4mm typically), but the settings will have to be absolutely perfect. Two layers is fine, and use three if you don’t trust your extruder and/or settings. Narrower walls will allow more flexible parts which will release the ice cube more easily. With the Flexion Extruder you can run a double-wall part at full speed and expect a perfect seal.

Molds won’t always be horizontal, so they need to seal in every direction. A mold will be fully-enclosed, and you don’t want to lose any water or the thing doesn’t work. Let’s say I want to make an awesome bomb-shaped jello shooter (see disclaimer at the bottom about the safety of Ninjaflex molds). Here’s the bomb I want to make:

The bomb!

This will require a two-part mold, and those parts will need to seal against each other. A basic flat-surface parting line probably won’t seal, even with a flexible material, and even if you clamp the two halves together. We need to add a labyrinth seal of some kind. We will add a tongue and groove around the perimeter of the part to make the path water has to take to escape much more difficult. Here’s how that looks:

Negative bomb

And here’s how the final print looks:

Ninjaflex bomb mold

These were printed in the orientation shown above. This actually helps us achieve a seal – the layer lines act as a micro- labyrinth seal in combination with the macro-seal of the tongue-and-groove. So this does actually hold water (when held together tightly), as proven by my jello shot

Custom jello shot, mostly

The tail fins tore off when I separated the two halves – mold release is an issue for another time. Maybe try cooking spray? This was just the first iteration – in the future I would keep my feature sizes larger when molding Jello (ice is definitely more durable.) I’d also make the tongue a little oversize relative to the groove to get a better seal without clamping. Of course when iterating a design it helps to be able to print fast – so get a Flexion Extruder and make your life easier! The model files can be found over on Thingiverse.

I guess there are is another category as well – manifolds? Think sprinkler toys or a faucet diverter. A faucet diverter that allows me to fill up tall water bottles in my bathroom sink would be pretty handy. Maybe I’ll work on that next. There are so many uses for flexible filaments!

Note: Ninjaflex is not food safe. You should never consume products molded in Ninjaflex. ExcelFil TECH Flex by Voltivo appears to be food safe, but do your own research.

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