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2.72 Elements of Mechanical Design

Spring 2009

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Schedule
Overview
‰ Syllabus

‰ Project

Groups
‰ Lab

‰ Project

Questions
Assessment

Reading assignment for next class:

‰ Shigley Mischke on shaft deflections & stress
• Sections 3.1, 3.2, 3.4, 3.7, 3.8, 3.10 – 3.11
‰ Refresh on beam bending
‰ Refresh on 1st and 2nd order system vibrations
© Martin Culpepper, All rights reserved 1

Purpose and pace of course

In-depth treatment of principles and practices required
to synthesize, model, design, fabricate & characterize.

APPLIED ENGINEERING
‰ Teaching emphasis, style and grades reflect this
‰ You will be expected to practice what you see in lecture

Reading ~ 50% of grade…

2/3 semester of lectures

© Martin Culpepper, All rights reserved 2

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Info sources: Teaching staff & texts
Prof. Martin Culpepper TA: Jon Hopkins

Required text: Mechanical Engineering Design (Shigley / Mischke)

Useful text: Design of Machinery (Norton)
Machinery’s Handbook
© Martin Culpepper, All rights reserved 3

Teaching philosophy
“The man who sets out to carry a cat by its tail learns something that will always be useful and which never
will grow dim or doubtful.” --Mark Twain

Thoughts, decisions & actions based on understanding:

‰ Models and their associated equations are idealizations
‰ Only “perfect” model is a physical embodiment
‰ The limits/power of modeling and simulation
‰ Mechanical system design is cost and time intensive.

Mastery of:
‰ Concepts, principles & design processes necessary, but not sufficient
‰ Math, physics and engineering models are necessary, but not sufficient
‰ Practical skills and best practices are necessary, but not sufficient
‰ The judicious use of (a), (b) and (c) is necessary

© Martin Culpepper, All rights reserved 4

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Design project
“In theory there is no difference between theory and practice. In practice there is.” --Yogi Berra
2.72 will focus on
(i) understanding concepts, principles, design process, best practices,
mathematics, physics and engineering modeling; and
(ii) rigorous application of the same to realize a complex and high quality
mechanical design.

You will learn by

(i) Doing…
(ii) Gaining insight via interaction with staff

Project:
(i) Teams of 6 work to model, design, build and characterize one lathe
(ii) You can all build copy in parallel, group must do at least one
(iii) Meeting functional requirements is critical to passing
© Martin Culpepper, All rights reserved 5

Project: Desktop lathe

© Martin Culpepper, All rights reserved 6

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Documentation
Images and video
‰ Take pictures/video as you go
‰ Due in soft copy on the day their corresponding hardware/results are due
‰ TA has camera if needed
You must keep a dedicated design notebook
‰ Keep your ideas, calculations, and records in one organized place
‰ Bring your notebook to all 2.72 events
‰ Notebooks will be collected periodically, used to generate final grades
‰ Legible and organized!
‰ Staple or glue in loose papers, no 3-ring binders will be accepted
‰ DO NOT take class notes in this notebook
Final report
‰ No more than 6 pages (not including appendices)

‰ Purpose = convince the staff that you learned & used the course material

© Martin Culpepper, All rights reserved 7

Mechanical laboratories
Disassemble mechanical devices/assemblies
‰ Take measurements, answer questions and reassemble
‰ Tools will be provided
‰ Bring your own safety glasses (we will give 1st pair)

Follow shop safety rules

Lab times
- Groups 1, 2 & 3 from 09.00pm – 12.00pm

- Groups 4, 5 & 6 from 02.00am – 05.00pm

Topic
1. Lathe disassembly
2. Bearing alignment
3. Transmission
4. IC Engine

© Martin Culpepper, All rights reserved 8

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Design laboratories
45 minute meetings
‰ 15 minute presentations

‰ 30 minute discussion/design review

‰ 50 inch plasma will be available

Everyone must present their part of the project

As a group:
‰ First tell us the purpose of the meeting

‰ Then immediately discuss Gantt chart

‰ Details of the work to date, calculations

‰ Have back up slides for deep dives

© Martin Culpepper, All rights reserved 9

Parts for the lathe

Our responsibility Your responsibility
Spindle • Housing blank • Housing • End cap • Shaft • Bearings
• Shaft blank • Preload mechanisms
Structure • Headstock blank • Rails • Finished tail stock
• Tail stock blank • Finished tube • Finished head stock
• Structure tube blank
Lead screw drive • Bearings • Preload tube • Drive nut • Drive preload nut
• Preload end cap • Lead screw bearing seat
• Lead screw • Bearing preload nut
• Preload washers
Carriage • Polymer bed blank* • End skirt blanks* • Finished polymer bed* • Finished end skirts*
• Handles • Drive flexure coupling • Bushing flexure coupling
• Bushings
*May cast 3 pieces as one, stay tuned…
Cross feed • Tool holder • Lead screw • Flexure bearing • Rear flexure mount
• Front flexure mount • Thrust bearing
• Proper dial mount surfaces/flats on screw
Miscellaneous • Chuck
• Metrology fixtures (3-ball & runout)
• HSS cutting tool
• Fasteners

¼ - 20 bolts – 0.50 inch long

¼ - 20 bolts – 0.75 inch long

¼ - 20 bolts – 1.00 inch long

© Martin Culpepper, All rights reserved 10

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Use of ME Mfg. shop
"Good plans shape good decisions. That's why good planning helps to make elusive dreams come true." --Lester Bittel

Open M-F, 8am-4pm, Clean up at 3:30pm

Use of the machine shop must be scheduled

‰ Lab time
‰ Monday, Tuesday and Thursday between 8am-12pm
‰ Wednesdays and Fridays between 1pm and 4pm
‰ 10 min. late for an appointment, your appointment will be cancelled.

Process plans
‰ 2D printed, CAD drawing with dimensions and tolerances (NO sketches)
‰ 3D printed rendering of the part (e.g. screen capture from CAD)
‰ Properly scaled DXF (see handout) on disc/e-mail to shop manager
‰ Completed process plan table
‰ Shop manager must sign off and then you turn into Culpepper
© Martin Culpepper, All rights reserved 11

Grading
Grading:
‰ 50 % Project

‰ 50% In-class and take-home mini-quizzes

All materials are due by 5pm

‰ Via e-mail to teaching assisstant, unless otherwise stated.

‰ Email errors will not excuse late assignments.

You must understand otherwise you are dangerous

‰ No student’s group may proceed w/o grade > 80% on qualifiers
‰ Make up quizzes may be given, but course schedules won’t change

Quizzes
‰ Take-home quizzes Reading quizzes In-class exercises

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Rules for collaboration
You should work together & learn from one another
‰ What you submit MUST be your own work unless it is specified as
a group submission. In the case of group submissions, everyone
that worked on the submission must sign a cover page and
provide bullet point summaries of what you worked on and how
much of that part you did

You MUST acknowledge the contribution of others

‰ For example, after working an assignment independently, you compare
responses with another student which alerts you to an error in your own
work which you then correct. You should state at the end of your
submission that you corrected your error on the basis of checking
responses with the other student. No credit will be lost if the response is
correct, the acknowledgment is made, and no direct copying of the other
response is involved.

© Martin Culpepper, All rights reserved 13

Course Web Site

http://pcsl.mit.edu/2_72/index.html

‰ Reading assignments

‰ Quiz materials

‰ Lecture notes

‰ Software downloads

‰ Homework downloads

© Martin Culpepper, All rights reserved 14

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Form groups & assign gurus
Group 1 Group 4

Group 2 Group 5

Group 3 Group 6

© Martin Culpepper, All rights reserved 15

Assessments
Assessment A
‰ On web

‰ 15 minutes

Assessment B
‰ In class

‰ 45 minutes

Can’t hurt you, only help – extra credit

© Martin Culpepper, All rights reserved 16