Scotch Yoke

Mechanism Model

Foundations of Product Realization - Spring 2019

Build a model of a mechanism, showcasing its function and motion. I chose the Scotch Yoke, a reciprocating motion mechanism that converts rotational motion into linear motion.

Concept Sketches

My ideation process for this project began in researching what a scotch yoke was - it was not a mechanism I had heard of before. Once I better understood the mechanism, I started ideating in themes as well as patterns but ended up settling on a geometrically defined theme, hoping to incorporate some dramatic angles into a mechanism that I so often saw rendered with curvature.


My early prototypes were quickly made and crude, but very insightful. After the first iteration, I learned that the scotch yoke relied on a very defined slot, and in my next version, I made a much narrower slot. In later prototypes I experimented with incorporating a dwell, which I ended up incorporating in my final.

CAD Parts

Although there were many different parts that went into this mechanism, the two that gave me the most trouble were the wall and the base, as I had to make sure that the base had holes that precisely lined up and supported the rest of the assembly. The main challenge when creating the wall was making cutouts for the captured nuts, which was a new fastening technique for me.

CAD Assembly

Once the assembly was created, it was much easier to see how all of the components came together. This stage was incredibly useful, as I was able to see how all of the fasteners would fit once all of the layers of various thicknesses were assembled together.

Engineering Drawings

For the engineering drawings, I decided to create part drawings for the base and wall pieces, as I found them the most intricate and specified parts of my assembly.

The assembly drawing was particularly rewarding as the angled views do a lot to communicate the intended building process and the multiple views give viewers a comprehensive understanding of the project.

Bill of Materials

Acrylic x 2 - $2

Duron and basswood - free, I used scrap material

⅛’’ shoulder screw - $1.25

¾’’ shoulder screw - $1.25

2 x 8-32 hex nuts - $0.04

4 x 4-40 1’’ machine screws - $0.12

4 x 4-40 hex nuts - $0.04

2 x 6-32 ¾’’ machine screws - $0.06

2 x 6-32 ¾’’ hex nuts - $0.04

1 x 10 washer - $0.03

1 x wave washer - $0.70

600 grit sandpaper - $1

Total - $6.53

Finished Product

Finished yoke with interchangeable sliders

Fasteners on display from behind

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