2.72 | Spring 2009 | Undergraduate

Elements of Mechanical Design


Images and Video

You must take pictures/video of parts, fabrication processes and experiments as you go. This includes pictures of every part you make, all sub-assemblies (e.g. spindle, carriage, etc.) and then the finished lathe. You must take:

  • At least one 10ish second video per part wherein some critical fabrication step is being conducted (e.g. turning)
  • At least one 30ish second video per sub-assembly describing how each was assembled, problems in assembly, etc.
  • At least one 60ish second video per test describing how each test was conducted and showing a result (e.g. run-out)
  • At least one 30ish second video showing both axes working as the lathe cuts aluminum

These images/video will be due in soft copy on the day their corresponding hardware/results are due. If you need access to a digital camera, the TA will provide one, but you must schedule this in advance and the camera may only be checked out for 24 hours.

Design Notebook

Do not use a spiral notebook, you must use a Lab Notebook. You must keep a dedicated design notebook so that you may store all of your ideas, calculations, and records in one organized place. You must bring your notebook to all 2.72 events. Notebooks will be collected at the end of the semester and then used to generate final grades, so please make sure they are legible and organized! Any loose papers must be stapled or glued in; no loose papers will be included in the grading. We encourage you to paste in pictures of the parts when appropriate. No 3-ring binders will be accepted.

Gantt Chart

Your group must have a Gantt chart that includes all course milestones, assignments, team, and design lab meetings with Prof. Martin Culpepper.

Design Verification Tests/Experiments

“Experience does not ever err; it is only your judgment that errs in promising itself results which are not caused by your experiments” — Leonardo da Vinci

You will be responsible for generating the design of your experiment, modeling/understanding/estimating the errors in your experiment, and creating the hardware that is required for you to measure:

  1. Spindle error motions (dx, dy, εx, εy, as a function of θz) on the shaft and on a part in the chuck
  2. Carriage error motions (dx, dy, εx, εy, εz as a function of z) as it travels along the z axis, or
  3. Cross slide error motions (dy, dz, εx, εy, εz as a function of x) as it moves long the x axis

You must use the CMM to characterize items 2 and 3. You may check out a 3-ball metrology fixture, consisting of three finely polished balls attached to a plate that should be mounted to the part that is being characterized, with the centroid of the balls located at a point of interest. By measuring the center of each ball at a specific location along the travel, you may identify the plane that contains the three ball centers, the centroid of the triangle that contains the centers and the normal vector to the plane. This is sufficient to calculate all of the error motions.

You must create a spreadsheet or equivalent simulation tool that calculates the error motions given the center point of the three balls. Bring this to the CMM training and measurement sessions so that you may key in your data and immediately see the results. This way you will know if you are getting reasonable results from your experimental setup! You can also use the spread sheet to see how sensitive the measurement set up is, given the errors in the CMM (very important).

Process Plans for Parts (Template PDF)

“Good plans shape good decisions. That’s why good planning helps to make elusive dreams come true.” — Lester Bittel

Before you fabricate a part, you must first meet with the Shop Manager to discuss how to make the part. You must schedule a meeting with him to obtain approval. Remember, he is busy with many classes so contact him early. Everyone who will work on the part must attend the meeting. You must then generate a process plan (see template) and keep this plan in your design notebook. When you go to fabricate the part, you must give the process plan to the Shop Manager for final review.

At a minimum, your group must bring the following to this meeting:

  1. 2D printed, CAD drawing with dimensions and tolerances (hand sketches are not allowed)
  2. 3D printed rendering of the part (e.g. screen capture from CAD)
  3. Properly scaled DXF on disc or e-mailed to the Shop Manager if your part is to be waterjet
  4. Completed process plan table (see template) wherein the following are laid out in bullet point form
    • Major steps that you will take to make the part, including fixturing and alignment steps
    • Tooling that you will need for every step
    • Measurement tools that you will need for every step
    • Questions/uncertainties

The Shop Manager must sign off on the top of the sheet and after the part is made, the process plan must be handed in to Prof. Martin Culpepper, at the D-lab meeting following the completion of the part(s). Process plans will be graded and supporting information (see items a and b above) must be stapled to the plan while item c (if applicable) must be emailed to Prof. Martin Culpepper.

Your group will need to schedule separate process plans for:

Spindle shaft, housing and end caps 30 minute maximum End of Week #2
CMM training (schedule with TA) 1 hour maximum End of Week #7
Flexures (Cross-slide & lead screw) 1 hour maximum Beginning of Week #8

You need to move fast!!!! If your group does not make these dates/deadlines, this will be reflected in your grades.

Final Report

A final report of 6 pages (not including appendices) is required. The purpose of the report is for you to convince the staff that you learned and used the course material properly. The contents of the report are up to the group; however it would be reasonable to include descriptions of your group’s activities, calculations, predictions, results, lessons learned and performance data - how did it do cutting an actual part? All reports are 12 point font, double-spaced and 1 inch margins. The reports will be due in MS Word format.

Course Info

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