(to tweak the dimensions of this model click on the Open In Customizer button, adjust as needed and saved the modified design)
Use this thing for safe disposal of X-Acto blades. Simply insert your used blades through the slot and when the bank gets full, close the slot with an adhesive tape, dispose it and print a new and empty bank.
The model has an internal guard that makes it difficult (but not impossible) to remove blades through the slot. If you want extra protection, pause the printing half way, throw in a small magnet (see picture, they are available on ebay and from many other sources) and continue the printing. This will keep the blades clamped to each other within the bank.
The model is oriented in printing position (with the slot at the bottom). When done printing, flip it over to expose the slot at the top.
I printed with PLA, 70C bed, 200C nozzle, cooling fan, 3 layers bottom, top and shell, 15% infill.