Some renders show this model in another colourway.

Keychain utility knife

A pocket knife for standard trapezoid blades whose blade springs home on magnets, with no spring inside.

Size closed, with the thumb pad: 63.2 x 31.0 x 8.0 mm
Blade: WORKPRO SK5 trapezoid blade, 61 x 19 x 0.6 mm
Print time: 0.8 h on 3 plates
Filament: 10.3 g

Colourway

PETG HF dark gray main
PETG HF white second
PETG HF lake blue accent

About the design

This is my keychain utility knife, 63 mm long and 8 mm thick, for the standard trapezoid blade. I push the thumb pad forward and the blade slides out of the nose, up to 13 mm of cutting edge. When I let go, eleven small disc magnets pull it straight back in, so nothing inside can tire or creep the way a printed spring does. The magnets sit in a band beside the blade's back edge, away from the steel, so they never drag the blade sideways or lift it. A small safe lock slides across in front of the carriage for the pocket, and a keyring hole sits in the tail. The base hooks into the tail and one small screw holds it, so a new blade goes in within a minute. Every part prints flat without supports. Check your local laws before you carry a knife.

What you can change

The blade's length, width, thickness and notches, to match the blade in hand
The clearance of the blade's pocket
The sliding fit of the carriage and the lock
The magnet pockets' clearances

Specifications

Size closed, with the thumb pad: 63.2 x 31.0 x 8.0 mm
Blade: WORKPRO SK5 trapezoid blade, 61 x 19 x 0.6 mm
Magnets: 11 x 5 x 2 mm N35 discs, 3 at the tail, 5 in the carriage and 3 ahead
Screw: ISO 7046-1 M2 x 6
Stroke and cutting edge out at the deepest stop (mm): 14 and 13
Return force at home and at its weakest (N), my estimate: 3.18 and 0.39
Weakest return over the weight and friction it beats, my estimate: 2.4
Height of the pause for the carriage's magnets: 3.38 mm
Printed parts (g), my estimate: 9.5

Printing

Plates, print hours and filament grams for each print project
Project	Plates	Hours	Grams
Keychain utility knife, PETG HF	3	0.8	10.3
Total	3	0.8	10.3

Times and weights come from slicing the model at 0.20 mm layers. Each figure is rounded on its own.

In the room