Hobby knife for ultra cheap blades

Use case

This folding knife uses the ultra cheap “break-off” blades that are made for the sliding knives sold in home improvement stores. These blades are significantly cheaper than the trapezoidal blades that I saw being used in similar designs. 

Design features

In contrast to other designs, which are glued together or use tight fitting bolts, I have chosen to use my self-designed printed screws. The design is tuned in a way that you can tighten the screw without restricting the movement of the parts. If you should want to replace the blade with a new one, you can just disassemble the knife by taking out the screw. It holds all parts together and keeps the blade locked in.

What parts do you need

You need: 

• all 5 printed parts (see “printing” below for details)
• one 18mm “break-off” blade, which sell for 10-30 cents per piece, depending on the package size 
• two round magnets 6x2mm, which I got for about 4 cents per piece 

Printing

All parts can be printed in the uploaded orientation. I recommend 4 perimeters and 40% infill. The bottom side handle and the bladeframe need supports (from build plate only). The supports on the handle did come off very nicely. The surface of the bladeframe may need a little cleaning once the supports are removed… a perfect application for the hobby knife … yes, I do see the chicken-and-egg problem ;-) 

Assembly

Prepare the blade first, by breaking off 5 segments, leaving 2 segments on the back part of the blade (this is the part that we will use). Glue in the magnets with superglue, one in each handle (make sure they attract each other once the knife is assembled). Slide in the blade with the back side first into the bladeframe until the hole in the blade and the hole in the frame match. Now lay in the blade holder, it's pin will hold the blade in place. Now you put the topside hande on the blade frame, sticking the dome with the thread through the big hole in the frame. Turn the whole thing around and put on the bottom handle. Now you can put in the screw and tighten it. Your knife is done.

Links

• A complete set of 3D printed screws and nuts, fitting to the one I used in this design.
• For reference, an Amazon link to the blades I used. I tested with another brand as well.
• For reference, an Amahon link to the magnets I used, I am sure other brands work as well.

(I am not affiliated to Amazon or these articles in any way, I provide these links just for reference).

Don't hurt yourself (or others)

A word of warning! These blades are extremely sharp. That is nice, but also dangerous. Be very cautious both during the assembly (and especially when breaking off the blade to the correct length) and when you use the knife. You do all this at your own risk.

Mind the environment

Don't throw away the rest of the blade. It is not wasted, as I have another project planned that uses exactly this part of the blade.

Happy printing!