Melissa Ma
Junior Mechanical Engineering Student @ University of Toronto | Engineering with a Purpose
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CNC Milling Machine
SolidWorks | Hand Drafting | Project Management | Leadership Skills | Research Skills
Designed a 4-axis milling machine for architects and small engineering firms that are looking to create prototypes.
Sketch of conceptual design
Design Specifications
Tomb Stone Mechanism
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Pinion gear drives a vertical motor, which rotates the tombstone about Z-axis
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Needle roller thrust bearing supports tombstone's translation about Y-axis via ball screws
Spindle Translation Mechanism
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A ball screw mechanism is composed of three main components, a nut, a screw with helical grooves, and ball bearings. This allows for the rotational movement to be translated into linear motion. Additionally, the ball screw is attached to the end support, which is coupled to the motors at the end
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This drives the spindle in the XY directions
Role
Mechanical Designer | CAD Designer| Team Leader
Project Highlights
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Created engineering specifications and selected parts from McMaster Carr
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Designed 7 mechanisms and the overall assembly in SolidWorks
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Created detailed 2D engineering drawings and 3D renderings
Tools
SolidWorks | Hand Drafting | Project Management | Leadership Skills | Research Skills
Results/Lessons Learned
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Successfully designed a 4-axis conceptual milling machine that met all specs, functions, and objectives as judged by the course teaching assistant.
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In a system with lots of moving parts, the accuracy of the system is determined by the least reliable mechanism. Therefore, we need to weigh the tradeoffs between reliability, performance, and cost of a mechanism/part in regard to the whole design.
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Rack and pinion may reduce the overall accuracy/precision of the system, but ball screws are more prone to buckle under vertical loads.
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The ball screw mechanism was chosen over other mechanisms that can translate rotational motion to linear motion, such as a rack and pinion, due to its high accuracy and low backlash. As the ball bearings are contained within the nut, they are self-lubricating, leading to very low friction. Furthermore, as the bearings are enclosed, no debris can interfere with them, making them low maintenance.
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Reverse engineering when choosing motors: based on the gear used, we can calculate the torque and required speed, and then check if specs are within the range of stepper motors. If a higher torque is needed, then look at servo motors. A gearbox is not required for any motors that can provide the speed and torque required. A gearbox can be used to reduce/increase speed.
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When researching different mechanisms, it is super helpful to watch videos on existing systems.
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When working on a group project, it's extremely important to communicate any issues that are preventing progress. Because our team didn't do this on time, it led to many delays in progress and rushed work towards the end.