Precision motion and adjustability
The X-axis combined dovetail guidance, a lead screw, gib preload, a custom indicator, anti-backlash features, way protection, and rotational adjustment.
Final cross-slide CAD.
MIT 2.72 · Elements of Mechanical Design
Axial Excellence Precision Lathe
A semester-long precision machine design project in which our six-person team designed, analyzed, manufactured, assembled, aligned, and validated a compact manual lathe for machining aluminum chess pieces. I contributed across the machine, with extensive involvement in CAD, detailed design, manufacturing, assembly, and testing.
Precision Machine DesignCADMachiningHTM ModelingTolerance & AlignmentTesting
01 · Overview
A complete precision machine, not a single mechanism
The spindle, X cross-slide, Z carriage, structure, drive system, toolpost, alignment features, and controls had to work as one system around measurable requirements.
The project combined analytical machine design with extensive hands-on manufacturing, assembly, measurement, and iteration.
Accuracy, repeatability, stiffness, cutting capacity, thermal behavior, actuation torque, durability, and manufacturability all influenced the architecture.
02 · Design
Architecture and analysis driven by measurable requirements
We used hand calculations, MATLAB models, error budgets, stiffness models, thermal models, bearing-life calculations, failure analysis, and state-point optimization to guide dimensions and architecture.
Spindle stiffness, preload, and thermal growth
The spindle design balanced shaft bending, bearing stiffness, preload, friction, fits, thermal expansion, speed, torque, and life.
Section view of the spindle assembly.
Analysis-driven design
Model the physics, then use the model to make decisions
Cutting-state optimization and stiffness/error budgets helped establish useful operating points and allowable deflections before hardware was finalized.
Cutting-state optimizationFeed rate, spindle speed, depth of cut, machining time, and motor power were evaluated together.
Measurable functional requirementsLater measurements checked whether the real machine behaved like the models and error budgets predicted.
03 · Build
CAD became hardware through machining, fit-up, and integration
I worked throughout the machine rather than on a single isolated part, moving continually between CAD, the machine shop, assembly, troubleshooting, and rework.
1
Detailed CAD
Revised geometry around interfaces, fits, preload, alignment, and manufacturing processes.
2
Manufacture
Machined and fabricated custom components, checking dimensions and fit.
3
Assemble
Integrated subassemblies while debugging friction, preload, interference, and alignment.
4
Measure
Used indicators, force measurements, CMM data, and cutting tests to drive tuning.
Assembly and integration
Final performance depended on getting bearing preload, shaft alignment, slide motion, structural stiffness, motor mounting, and tool-to-spindle position right together.
Subsystem validation
Subassemblies were checked independently before integration so fit, friction, alignment, and manufacturing issues could be isolated.
04 · Test & Iterate
The machine was measured, cut with, dropped, and tuned
Early smoke-test results exposed accuracy and repeatability problems. The team adjusted rail angle and rotational alignment, reduced taper, and repeated measurements until the final requirements were met.
15 µmX repeatability
45 µmZ repeatability
47k lb/inX carriage stiffness
66k lb/inZ carriage stiffness
4 ftdrop test survived
Taper improved from roughly 0.3° to 0.07°.
Dial-indicator adjustment of the Z-axis rail angle and cross-slide rotation, followed by CMM verification, moved final accuracy and repeatability inside the project requirements.
05 · Result
Precision came from the whole chain
The project demonstrated that precision comes from architecture, constraint, stiffness, thermal behavior, manufacturing, assembly, adjustment, measurement, and iteration working together.
