LDUK v6 - Light Duty Utility Knife

Obvious disclaimer

The LDUK (Light Duty Utility Knife) is designed for light-duty tasks such as opening letters or parcels. It uses standard utility blades, which are extremely sharp!  Handle with care, keep out of reach of children, and always retract the blade when not in use. This is shared only for information purposes for free as-is, without any warranties, as a design experiment. If you decide to print this, you do so at your own risk and are solely responsible for any injuries or damages resulting from the printing or use of the knife.

Description

The LDUK is a 3D-printable, ultra-light utility knife designed for casual office and urban tasks. It was initially born out of my frustration with the lack of left-handed utility knives, but it evolved into much more than that. The design is simple, satisfying, and highly functional. The LDUK uses standard utility blades, features a satisfying deployment mechanism, and is optimised for quick, support-free 3D printing, making it an accessible and practical addition to your kit.

Features

• Ambidextrous Design: Configurable for optimal use in either hand, perfect for left- or right-handed users.
• Magnetic Deployment: Two embedded magnets ensure smooth, predictable, and satisfying blade extension and retraction.
• Ultra-Lightweight: Weighing only 12 grams (and that includes the stainless steel blade!)
• Tool-Free Blade Swap: Easily load, turn, or replace standard utility blades without additional tools.
• Blade Visibility: A cutout allows you to confirm the blade is loaded correctly.
• Ergonomic Curves: Rounded edges and chamfers provide comfort, with a design cue indicating the blade’s exit point for safety.
• Magnetic Storage: Sticks to metal surfaces for convenient, space-saving storage.
• Durable Design: The blade is suspended to avoid riding on plastic, enhancing longevity despite being printed in PLA.

BOM

You will need magnets and the right blade for this. Affiliate Links to grab the components (if you want to use them):

Note: not all utility blades are made the same! Some are 63mm - this does not work with those.

Printing Notes

• You won't need supports for any of this. It prints in PLA just fine.
• You can choose either the left or the right handed configuration - the body and the caddy are specifically designed for your thumb position.
• Ideal orientation for caddy will be on its side, so you might want to add a brim and clean the edge up afterwards for a smooth glide. Check photos for my recommended print orientation.
• Depending on your slicer, layer height and settings, you must add a PAUSE just before the ceiling of the cavities inside of the body is printed over - this is essential. Make sure you are careful and watch tutorials on this if you've never done it before.
• Both magnets in the body must be oriented in the same direction for this to work as intended!
• Make sure both magnets you place inside of the body are oriented in the same way!
• Ensure your printer is well-calibrated, as tight tolerances are critical for smooth blade movement. If the mechanism feels stiff, lightly sand the blade caddy or adjust slicer settings (e.g. horizontal expansion).

Assembly Notes

1. Print the body and blade caddy for right/ left hand (remember the PAUSE and the 2x body magnets). Gather a standard utility blade and a neodymium magnet for the caddy subassembly.
2. Carefully slide the blade into the caddy in the right orientation (the window will show you how much you have to push it in until you hit the wall). Always use adequate protection when handling the sharp blade - especially as 3D printing tolerances are always unpredictable!
3. Once the blade is set, place a magnet in the circular hole in the caddy, so that it rests on the blade.
4. Slide the caddy + blade subassembly into the body.
5. If the body doesn't suck in the subassembly, you may have to turn the caddy magnet around.
6. Test the deployment and retraction to ensure smooth motion. If it’s too tight, lightly sand the caddy’s edges.
7. Always retract the blade before storing to prevent accidental exposure. Remember, the blade is not locking by design - although the magnets are strong for this application, always assume that it may deploy itself, given enough force.

Thank you for checking out my design! Hope you enjoy this. Stay safe, and happy printing!