Box Cutter with Smooth Operation

thingiverse

This is a remix of the excellent design #5327492 There were three aspects I wanted to improve: 1. I thought that the actuation distance was more than necessary and risked plastic deformation of the lever arm over time. 2. When sliding the "handle" out or in, the catch would very often snag on burrs on the blade, requiring the user to wiggle the blade directly to free it up. 3. When sliding the "handle" back in to the seated position, the blade rotates very slightly, which causes the point near the keyring to cut in to the groove. Again the only way to free it up is to pull on and wiggle the blade directly. To solve #1, I lowered the top surface of the catch by a bit over 0.5mm. To solve #2, I rounded the top surface of the catch and the bottom surface of the pin holding the blade so that the two surfaces would engage and slide over one another instead of catching on the burr of the blade. To allow clearance for the pin, I created a slightly recessed channel in the sliding surface. To solve #3, I made the overhang 60 deg instead of 45 deg for the short section of the "v" groove near the keyring. My printer can easily handle a short, 60 deg overhang, so this didn't require adding supports. By making the angle 60 deg, I was able to "move" the bottom edge of the slot far enough toward the edge of the part that the blade point never catches when the blade is slid back, even if it twists slightly. Overall, I'm very happy with the result. The overall dimensions and principle of operation of the the original design were preserved, as was the ability to be printed simply without needing any supports. Operating force is slightly less than the original, which I like, but most importantly, the blade never binds. The "open" and "closed" positions are secure enough for me, as an adult, to prevent slippage during use or accidental actuation when not in use. However, it is easy enough to actuate that it should never be left within reach of a child. I think the original warning/disclaimer was well stated, so I'll repeat it here: I only provide the design. The handling of the item and any blades used is your own responsibility. I assume no liability for property damage or personal injury.