Box Cutter

A playful spin on a clastic tool using principles from mass production.

There were four primary project goals:

• Intuitive design
• Tactile extension and retraction mechanism
• Replaceable blade
• Simple and cheap to make

The two halves of the injection-molded knife case are joined with press-fit bosses to facilitate toolless assembly and repair. I ran plastic flow simulations to predict weld lines, identify air traps, and refine part geometry and gate placement to improve moldability. I then used 3D CNC milling to machine the molds from aluminum blanks and made injections using a Morgan-Press G100-T. Despite some cosmetic sink marks, the parts met all functional requirements.

The aluminum grip clips over the plastic case and engages with the blade thumb stud. A flexure built into the base of the grip provides resistance and a tactile snap when the blade locks. The sheet metal blanks were bent with custom form tools and then powder coated.

Costing less than $4 per unit in materials and labor, the design met all of the project requirements and gave me an opportunity to apply DFM principles to an actual marketable product!