2.72 | Spring 2009 | Undergraduate

Elements of Mechanical Design


Project Description

“In theory there is no difference between theory and practice. In practice there is.” — Yogi Berra

The content of 2.72 has been scoped to include the majority of mechanical elements that are considered ubiquitous components of mechanical systems. All of these mechanical elements may be found in mechanical systems that could be the subject of a 2.72 design project. We have elected to use a desktop manual lathe as the 2.72 design project. This selection offers the unique opportunity to create a mechanical system that: (a) forms the basis of your assignments and laboratory activities (b) will be used to draw inter-related examples that demonstrate component/system design (c) you may keep as a “memento” of your mechanical design experience and accomplishment; and (d) you may use to create mechanical elements for future activities.

Lathe CAD (ZIP - 19.0MB) (This ZIP file contains: 6 .stl files, 1 .dxf file, 7 .sldasm files, 5 .slddrw files, and 31 .sldprt files.)

Responsibility for Parts


Housing blank
Shaft blank

Preload mechanisms
End cap


Headstock blank
Tail stock blank
Structure tube blank

Finished tube
Finished tail stock
Finished head stock

Lead screw drive

Preload end cap
Lead screw
Preload washers
Preload tube
Lead screw bearing seat
Bearing preload nut

Drive nut
Drive preload nut


Polymer bed blank*
End skirt blanks*

*May cast 3 pieces as one, stay tuned…

Finished polymer bed*
Drive flexure coupling
Finished end skirts*
Bushing flexure coupling

Cross feed

Tool holder
Lead screw

Flexure bearing
Front flexure mount
Proper dial mount surfaces/flats on screw
Rear flexure mount
Thrust bearing


Metrology fixtures (3-ball & runout)
HSS cutting tool

¼ - 20 bolts – 0.50 in long

¼ - 20 bolts – 0.75 in long

¼ - 20 bolts – 1.00 in long


Deliverable Schedule

“Let our advance worrying become advance thinking and planning” — Winston Churchill

All parts, models, measurements, document drafts/components, and presentation drafts/components must be started/finished no later than the following respective dates. You are responsible for (a) arranging all required meetings, (b) scheduling required resources, (c) placing timely orders for parts/materials, and (d) fabricating/calibrating the experimental setup. Don’t get frustrated if you get stuck. Ask for help so we can keep you moving. We reserve the right to (and we will!) ask you for proof of start/finishing at random intervals. If you are not on schedule, this will be reflected in your grade, no exceptions.

Fabrication task dates
Spindle shaft Ses #3 1 day before Ses #6
Housing Ses #6 1 day after Ses #9
Housing end caps Ses #6 1 day after Ses #9
Cross-feed flexure Ses #8 Ses #14
Lead screw flexure Ses #8 Ses #14
Error model task dates
List of spindle error sources Ses #3 Ses #7
Model individual spindle errors Ses #3 Ses #10
Finish full spindle error model Ses #3 Ses #11
List of flexure error sources Ses #8 1 day after Ses #13
Model individual flexure errors Ses #8 1 day after Ses #13
Finish full flexure error model Ses #8 1 day before Ses #16
List of drive error sources Ses #11 1 day before Ses #16
Model individual drive error Ses #11 2 day before Ses #20
Finish full drive error model Ses #11 2 day before Ses #20
HTM-based lathe error model (in report) Ses #5 Ses #24
Measurement task dates
CMM training 1 day after Ses #9 1 day after Ses #13
Spindle error motions 1 day after Ses #9 1 day before Ses #12
Cross slide error motions Ses #13 1 day before Ses #16
Carriage error motions Ses #16 1 day before Ses #21
Report results and conclusions
Outline (text, table & figure placeholders) Ses #14 3 days before Ses #20
Images 1 day after Ses #3 1 day after Ses #21
Tables Ses #6 1 day after Ses #21
1st draft in separate modules Ses #16 1 day after Ses #21
Integrated, final draft Ses #22 Ses #24
Design notebooks 1 day after Ses #1 Ses #24

Group Budgets

“It’s clearly a budget. It’s got a lot of numbers in it.” — George W. Bush

Each group will be allowed to spend up to $200 to purchase bearings, preload washers, rails, bushings, epoxy, etc. The TA will order them for you from McMaster. You must provide the (i) part number, (ii) name/description, (iii) quantity and (iv) cost. If you find that it is necessary to purchase items from another source, you must also provide the name, address, and phone number of the vendor. We encourage you to use McMaster. Other sources will only be allowed if there is a compelling reason. Materials will be shipped to the TA via 3-day ground and you may pick them up from the TA’s office.

Measurement Tools in Prof. Culpepper’s Lab

“It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail.” — Abraham Maslow

You need to use capacitance probes and a data acquisition system to measure your spindle’s error motions. Given the delicacy of the probes, you must set up a meeting with the TA in order to run this experiment. You may arrange up to 2 hours per meeting per group. The TA will help you set up the probes and the data acquisition system. The TA will have a pre-arranged program that takes the measurements and exports data to a TXT file that can be imported to Excel or MathCAD.

Measurement Tools in the Shop

In addition to the stocked measurement tools in the shop, you will have access to special purpose tools that were purchased for this project that will make your job easier. See the Shop Manager to check them out. They must remain in the shop or adjoining computer room.

Two dial bore gages (for measuring the internal diameter of your spindle bearing bores)

Two digital micrometers (for measuring spindle shaft diameters)

Group Gurus

Your group needs to assign people to be responsible for the administration and conduct of certain tasks.

CAD Guru (SolidWorks)
FEA Guru (To be trained in structural, thermal, and vibration modeling in CosmosWorks)
Financial Guru (Budget and ordering)
Measurement Guru (CMM and various measurements)
MathCAD/Matlab Guru (Parametric modeling)
Documentation Guru (Pictures, video, etc…)

Course Info

As Taught In
Spring 2009
Learning Resource Types
Problem Sets
Lecture Notes