Manufacturing and Assembly - JG
For my mechanism I decided to use 3D printing and laser cutting as my primary methods of manufacturing. These methods are quick, free for students, and easily accessible on campus. For the links I decided to use ¼” wood to ensure it would hold up to the stresses applied on the mechanisms. I used the laser cutter to cut out each link so that all of the joint holes were accurate and the pins could be friction fitted where needed. Below is a short clip of the laser cutting process.
For the joints I decided to use 3D printing to keep me from making a trip to the hardware store, and to allow me to print several test joints to see how each one would work out. By using plastic joints with wooden links I hoped to achieve a mechanism with low friction. I knew I could also sand both the wood and plastic to increase their ability to slip easily when in contact with each other. Below is one of the models I used for my joints, featuring a large diameter to ensure strength and a good friction fit.
I also 3D printed my grounding component, which was one of the most crucial parts of my mechanism. This needed to be completed in two parts as it was too long to fit on the printer bed, so I designed a friction fitted pin to attach the pieces. I decided to use 3D printing rather than laser cutting for this component because of my link 4 and ground connection. This needed to be a sliding block type of joint, which would be too difficult to laser cut and not as accurate if machined by hand. 3D printing allowed me to design a very accurate ground connection that would perfectly fit my link 4.
While assembling the final mechanism I found that sanding down the edges of the wood became very important for the sliding joints. While the laser cutter provided a very accurate cut, the surface was rough and burnt. I was able to sand this down using 120-400 grit sandpaper. After sanding down all of the surfaces, I found a major decrease in the amount of friction in the mechanism. While I could have continued to sand down the surface, the 400 grit provided a smooth enough finish to minimize the friction.
My original plan for attaching the joints involved designing the link/ground holes in such a way where some holes would friction fit the joint while others allow the joint to rotate freely. While this system worked at first, I quickly found that the stresses during the quick return cycle were too high, and the joints could come loose. To fix this, I simply added a bit of super-glue at each of the friction fitted points which solved the issue. Several spacers were also used to help keep all of the links in line with each other and not rub into the joints or grounding component.