Nutcracker

thingiverse

Of all the nutcrackers I have encountered, the best are those with a wooden body in the shape of a cup and a wooden threaded plunger bolt that screws into the side of the cup to crush the nut between the end of the plunger and the inside of the cup. The advantage this design has over lever-based nut crackers is that once the nut's shell fails, it is easy for a lever-based nut cracker to go on and crush the rest of the nut, while screw plunger versions do not. This nutcracker was designed specifically for FDM printing in PLA without any support. A key detail I wanted in this design is that the load-bearing face of the screw thread should be as perpendicular to the load as practical. A more traditional steeply sloped face on this side of the thread would increase friction under load and that would be undesirable in a nutcracker. Testing various cup designs eliminated the possibility of printing with the threaded hole oriented vertically; the end always cracked along layer lines, even when printed solid. This suggested that the cup had to be printed horizontally, and so with the threaded hole in an orientation that would suggest its upper surface would need supporting. To avoid this, I re-designed the threaded hole in the body so that its upper surface is bridged and does not need support. The cup body also has internal hollows that are intended to increase its rigidity. So far, I have tested this nutcracker by cracking 1kg of mixed nuts (walnuts, hazelnuts, Brazil nuts, and almonds). The nutcracker survived this testing and showed no signs of damage on the surfaces that contacted the nuts. Obviously, the almonds offered most resistance to being cracked, and one of these prompted me to lubricate the thread, which I did by rubbing some candle wax on the thread. Candle wax has the advantage in this application that it is a good enough lubricant and is not inherently sticky, so it does not attract or accumulate nut dust. I would strongly recommend against using this (or any other plastic) nutcracker to attempt to open Macadamia nuts. The forces required to open them are too high, and remember that when PLA shatters, it shatters into very sharp fragments. The nutcracker is in three parts: a body, the threaded plunger, and a handle to go on the end of the threaded plunger. The plunger is designed to fit tightly into the socket in the handle; it should stay in place if firmly tapped down into the handle with a rubber or wooden mallet (or, say, the end of a rolling pin). However, if some Cyanoacrylate (CA or "super") glue were first applied to the inner surface of the socket in the handle, the plunger would really never come out again. The 3D models are oriented in the STL files in the way that they should be printed. The body needs to have its flat underside flat on the print-bed. The plunger needs to have its narrow end flat on the print-bed so that the threads do not need support (this may suggest printing with a brim for stability). In principle, the handle could be printed the other way up, but it prints fine in the orientation that it is defined in the STL file. The one I tested was printed in standard PLA using: 0.4mm nozzle, 0.2mm layer height, 15% infill (rectilinear), 3 perimeters, 4 bottom layers (0.8mm), and 4 top layers (0.8mm). The total nutcracker weighed approximately 110g (yes, that is more than 10% of a roll of filament). If anyone thinks they would like to guarantee that theirs was stronger than this, I would recommend increasing the number of perimeters before increasing the infill percentage.