Banana Piranha - A tool for opening bananas

Banana Piranha is a tool for opening bananas. A small hidden blade makes a cut in the banana skin, which makes it effortless to peel. When the arm is folded back the blade gets securely locked in place. Banana Piranha has a loop at the back so you can put it on your key chain.

Before printing, I recommend checking out the YouTube demo / instructions:

Print Instructions

This is a fairly involved print with several steps. You'll need a printer with good bridging capabilities. I've successfully used a Prusa I3 MK3S+ with PrusaSlicer for printing all parts. 

All parts should be printed without supports.

If you use PrucaSlicer, you can get the same print settings I used for each part by opening the 3mf files and selecting action “Open as project”.

Additional materials

The build requires two non 3d printed parts:

• Two segments from a 9mm snap off blade knife.
• A compression spring from a ballpoint pen.

The spring length must be about 30 mm. The diameter should not exceed 5.5 mm. If the spring is shorter than 30 mm you can stretch it out a bit to make it the correct length. 

You will also need to cut a 36 mm long piece of standard 3d printing filament (1.75 mm in diameter). It will act as a guide for the spring inside the mechanism.

3d printed parts

The build uses three functional 3d printed parts:

• “Blade Holder”
• “Pusher”
• “Body”

There are also two auxiliary parts, which are only used during the build process:

• “Filament Measure”
• "Print Support"

The part "Filament Measure" is used for precisely cutting the 36 mm length of filament.
"Print Support" is placed inside part "Body" during printing, together with the mechanical parts. It helps with bridging and holds the parts together during the print. After the print is finished the "Print Support" part is removed.

Settings for parts "Pusher", "Blade Holder" and “Print Support”

Recommended layer height: 0.2 mm
Recommended material: PETG
Supports: No (Optional for “Print Support”)

If you use PLA for part "Body" it's a good idea to print all these parts using PETG, since the two materials don't bond easily. This should eliminate the risk of the parts getting fused together. (That being said I've never had a print fail when using PLA for all parts.) The flexibility of PETG also makes the snap action of the pusher more satisfactory.

The part "Blade Holder" must have a pause at layer 8 (assuming 0.2 mm layer height), for inserting the 9 mm blade.

Settings for part “Filament Measure”

Recommended layer height: 0.3 mm
Recommended material: PLA
Supports: No

Settings for parts “Body”

Recommended layer height: 0.3 mm
Recommended material: PLA
Supports: No

If you have the "skirt" option enabled in your slicer, the "distance from object" option must be set to at least 10 mm. Otherwise the skirt will interfere with the "Print Support" part that will be placed mid print.

To reduce the risk of bridges failing I recommend to use PLA for this part. In PrusaSlicer I also enabled the option “Thick Bridges”.

Printing of this part includes one mandatory pause for inserting the mechanical parts. There are also two optional color changes.

Assuming 0.3 mm layer height:

• First color change at layer 3
• Pause at layer 35
• Second color change at layer 39

If you use PrusaSlicer I recommend turning on the “Ironing” option for this part, to improve the surface finish.