Final Design

The assembly of the scalpel is described as seen in the figures to the left

• •  As the shaft being held upside down, the two blades would slide into the wedges vertically. This would be the only period that pathologists need to make direct contacts with the blades. 

  • While the blades are sitting in the wedges due to gravity, two sockets would follow the same track to slide into the wedges and squeeze the blades.  

  • As both the blades and sockets are in position, the collet would be tightened along the threaded shaft and pushes the sockets. 

  • By applying force vertically on the sockets, they would also squeeze horizontally due to the design. Therefore, the blades would be well-constrained in both directions.   

In terms of performance, several 3D printed parts were physically tested.  During the testing, the wedges of several 3D prototypes were susceptible to breaking.  The weak points were taken note of and led to an elementary FEA analysis.

As the collet applies force vertically on the socket, the socket would also exert force horizontally on the blades (as demonstrated in the previous graph). In addition to that, a potential torque is applied on the wedge, which would lead to the wedges breaking. 

After consulting the instructor, it was noticed that the this is primarily due to the weakness of the 3D printing material. This was confirmed when the weak points of the design were eliminated in the aluminum prototype.