During the Spring of 2019, I worked on designing a desktop lathe within the context of MIT’s 2.72 Elements of Machine Design class.
2.72 is an advanced course on modeling, design, integration and best practices for use of machine elements such as bearings, bolts, belts, flexures and gears.
Our project covered the process machine design, modeling, analysis, calibration and evaluation in order to meet the following functional requirements:
- 50 microns repeatability
- Cuts aluminum parts up to 1.5 in diameter
- Withstands shock loads for drop test and hammer strike
The Team
Our team was composed of five undergraduate students. While all team members engaged in various design, modeling, machining and measurement activities, each one of us was responsible for an area of expertise.
As measurements guru, I was responsible for overseeing experimental setup design and measurement plans to ensure our lathe meets its functional requirements.
The Lathe
Our final product, Lathaniel, was able to compete and win at the final turning competition by achieving the highest precision and fastest cutting time.
Repeatability Measurements:
- Turned radius: 34 microns
- Turned length: 38 microns
- Taper: 12.7 microns
- Eccentricity: 38.1 microns
The Process
Spindle Design
The spindle shaft is the rotating axis of the lathe. In order to ensure exact constraints , the shaft was mounted with two Timken roller bearings in back-to-back configuration to allow for heat dissipation. A thermal study was performed to verify that this configuration is thermally stable.
The spindle shaft and housing were machined in-house on the lathe and GD&T specifications of radial runout were verified using measurement tools.
Once the spindle was assembled, various loading measurements were performed to evaluate the system’s stiffness and estimate resulting errors.
Cross-slide
The cross-slide is the component that allows for motion perpendicular to the axis of the parts we are trying to turn.
The design of the flexures in this component allows us to constrain the motion within the cross-slide to translation in one axis.
Finite Element Analysis was performed to ensure adequate performance of the cross-slide under the expected functional and shock loads.
Dancing Man Flexure
The dancing man flexure is a critical component of the design of the lead screw, which allows for movement in the direction to and away from the chuck in the lathe.
The dancing man flexure allows to alleviate the over-constraints that occur when assembling the lead screw to the lathe carriage thanks to its 4 degrees of freedom.
Finite Element Analysis was performed to ensure adequte performance of the flexure under loading conditions.
The original design of the dancing man flexure was based on the following paper by Hopkins and Culpepper.
Assembly
☠️ Death Test
To put our lathe to test, you can see our professor here striking the lathe with a hammer to ensure that it can withstand the impact to the spindle. Our lathe also withstood a fall from a desk's height and was able to function properly after the impact.
