Week 16: Wildcard Week

Assignment: design and produce something with a digital fabrication process (incorporating computer-aided design and manufacturing) not covered in another assignment, documenting the requirements that your assignment meets, and including everything necessary to reproduce it.

Custom coupler fabrication using the lathe machine

As part of Wildcard Week, I used the centre lathe machine to manufacture a custom mechanical coupler for my final project. This component acts as the interface between the MG90S servo motor and the rotating mechanism of the gripper assembly.

The part was machined from a cylindrical stock by first turning it to the required outer diameter and then creating a precise central hollow bore. Each side of the coupler was designed with a different purpose:

• One side was machined with a recessed hole to accommodate a fastening screw. This allows the coupler to be securely mounted to the rotating shaft, preventing any unwanted movement during operation.
• The opposite side was machined to match the spline profile of the MG90S servo horn. This pocket allows the servo's output gear to fit tightly into the coupler, creating a positive mechanical lock that efficiently transfers the servo's rotational motion to the gripper mechanism.

Machining this component on the lathe provided significantly better dimensional accuracy and concentricity than would have been possible through 3D printing. Since the part transmits torque directly from the servo motor, maintaining precise tolerances was essential to eliminate backlash, improve alignment, and ensure reliable power transmission.

This exercise also strengthened my understanding of lathe operations, including facing, centre drilling, boring, internal diameter machining, and achieving accurate fits for mating mechanical components. The finished coupler became a critical part of the final project by providing a strong and reliable connection between the servo motor and the rotating gripper assembly.

Before machining, I sketched the coupler with its key dimensions (overall length 14.25 mm, outer diameter 12 mm, and the bore sizes for each end) and kept the sketch next to the machine as a reference.

The coupler was turned on a conventional centre lathe in the workshop.