Abandoning rubber band flexible mechanism as too weak, I started thinking about using the 3D printed plastic itself as the compliance mechanism. I’ve long lamented about the lack of rigidity in 3D printed plastic, now is my chance to turn that flexibility to my advantage. Thus was born the second pen holder iteration, using two printed plastic links in parallel to keep the pen vertical.
Most of the thought went into how to print these links so that they could move independent from the underlying base. I toyed with the idea of printing support structures, or have them hang in air and take my chances, before I realized I could take another long-standing headache of 3D printing and turn it to my advantage. The weakest part of a 3D print are the bonds between layers. When a part starts to fail, it almost always fails along layer lines. So I will print this design in one piece, fully planning to break the two printed plastic links apart at the layer line to achieve my goal of two flexible links.
I printed these links across the entire width of the space I had to work with, because I thought longer links will shorten horizontal deflection as the links bend. As it turns out, such horizontal deflection was not the most significant problem. The two parallel links did indeed constrain motion along X-axis, and allowed pen movement along Z-axis, but it was not very resistant to forces along Y-axis.
At this point I ran out of time to create yet another iteration of pen holder before the SGVHAK meet, so I brought this print with me to test on the machine.
Roger Cheng (@Regorlas) October 07, 2019