PM - Manufacturing and Assembly

This section focuses on the refinement of our manufacturing process. It begins with a critique of our preliminary method and then transitions to our final process. Lastly we conclude with our lessons learned.

Preliminary Method

Our initial method involved laser cutting acetal delrin sheets (12"x12"x1/4") for our long, planar links. 3D printing was reserved for parts with intricate geometries such as our custom gears. 

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Upon inspection of our laser cut links, we discovered visible heat damage and material expansion. See the image below

  These Photos show the lack of precision and visual aesthetic that was achieved when using laser cutting.

Furthermore, the laser cut holes in our delrin were slightly angled and lacked concentricity. This complicated the press fits on our rods and bearings while adding additional alignment issues. We did expect this complication; however our method for expanding those holes with a drill press did not yield desired results. The accumulated error from this process prevented assembly of our first prototype. 

After this prototyping mishap, and considering time constraints, we decided that instead of making a "final prototype" , that we would make a "working prototype" and this proved to be the most beneficial approach. 

Final Method

Upon reevaluation, we concluded that CNC milling is the best method to machine our parts. Not only is the CNC mill more accurate and precise than the laser cutter, but it also did not leave burn scars or expand our material. Moreover, the precision offered by the CNC mill enabled us to press fit our rods and bearings securely.

We would like to thank and acknowledge our classmate, Michael Bettatti for lending us his expertise and advice in CNC milling. By doing so, he facilitated our manufacturing, design, and assembly.

Lessons Learned

There were a variety of challenges we encountered during the manufacturing process. The most infuriating was receiving bent stock delrin sheets. We quickly learned that our full assembly would only be as good as our raw parts; and unfortunately, the effect of the bend carried through the entire design. Had we set out to CNC our parts initially, we would have opted for aluminum sheets instead. Additionally, the 3D printed gears proved to be weak parts and susceptible to chipping and bends. Furthermore, the printed part tolerances were variable between printers and between print jobs. We could have eliminated the need for 3D printed parts had we selected standard gears off of McMaster and designed our project around them.