An M3 balisong I designed in Blender. The blade shown is a blatant copy of the Fellowship Blades Medusa's blade style. I didn't copy dimensions, only the shape. Printed the blade with California Filament Black PETG and the handles with Eryone Matte Navy Blue PLA. 

___

It requires 2 M3 nuts, 2 M3x12 screws(any head that fits), and 7 6x3mm magnets(for weight). 

The model is printed in 5 parts: the blade, 2 handles, and 2 bushings. The bushings are intentionally oversized so that the handles can be screwed down tight without binding on the blade. 

The blade is 4mm thick, and I've had the best luck with 4.5mm bushings. The holes in the blade to fit the bushings are 8mm diameter.

The bushings are as simple as a 7-8mm⌀/4.5mm↕ cylinder with a 3-3.25mm⌀ hole. If your bushings have considerable room to move in the blade or the screws considerable space to move in the bushings, then your handles will clack and will hit your blade. I have had a fair bit of struggle getting bushings that fit off of my Ender 3, but it can be done.

___

Honestly, this thing sorta flips pretty well in my opinion. It's not as good as my metal trainer, but it's almost more fun. I also have not needed to lubricate the model at all, as my PETG bushings seem to self-lubricate very quickly. It does have tap as the PETG blade is mildly flexible, but the handles never hit each other or the blade on mine(after 4+ weeks flipping). 

___

My only recommendation for printing orientation is that you DO NOT put the magnet holes of the handles on your print bed. That orientation is gonna be SUPER prone to cracking around the hinges. You can probably get away with it if you have really good layer adhesion, but it's not recommended. 

___

I'll try and get a decent clip of my flipping and upload it at some point(I'll probably forget this).