In 2.72 (Elements of Mechanical Design), we were tasked with designing components of a desktop lathe. The requirements given by the staff were:
The machine must cut 12L14 steel with a material removal rate of 0.08 in^3/min
Achieve surface finishes of 63 micro-inches
Have cutting repeatability of 50 microns
For this project, my specific responsibilities for the project were:
Determine functional requirements for subsystems based on metal cutting theory
Calculate spindle bearing life and heat generation from manufacturer's data sheets
Choose grease and pulley specifications for spindle based on life and heat calculations
With our design, we designed bearing spacing, axial preload, bearing grease viscosity, and pulley sizes to:
Keep predicted repeatability error from the spindle assembly within 21 microns
Exceed required life by a factor of 68
Stay within our budget of $150
We would have continued to design the the cross-slide and z-slide components, but COVID-19 interruptions limited our design to the spindle only. For this same reason, we were also unable to test the spindle to confirm its stiffness.
Below are my slides from a design review for the spindle. The slides show the justification for grease and pulley specifications and how they meet functional requirements.