Vertebrae Go/No-Go Hex Nut Problem

Written By David Oh

Output: Inspection tool, Data analysis

Field: Quality Control

Technical Skills: Inspection techniques, Quality Control, Tolerance analysis, CAD design

Soft Skills: Technical Communication, Repeatability, Process Improvement

Equipment: CAD software, Calipers, some hex nuts

Timeline: 1 week

Problem

Wayne Enterprise is developing a new vertebrae device that requires off-the-shelf hex nuts to fit precisely into a designated slot. However, standard nut manufacturers only control the inner diameter—they don’t care about the outer diameter or thickness.

As a result, some nuts won’t fit, while others are too loose. Simply inspecting by hand is slow and unreliable.

Wayne Enterprise needs a fast, repeatable way to ensure only properly sized nuts are used.

Your job is to develop a Go/No-Go gauge to quickly identify acceptable parts.

  1. Buy a set of at least 10 hex nuts 8-32.

  2. Measure the largest outer diameter (corner-to-corner) and thickness of each nut.

  3. Find the average outer diameter and thickness

  4. Determine tolerance limits for Go/No-Go inspection via empirical rule for normal distribution to get at most 70% of the hex nuts

    1. Empirical Rule: 68% of the data falls within one standard deviation of the mean, 95.45% of the data falls within two standard deviations, and 99.73% of the data falls within three standard deviations.

  5. Design a Go/No-Go gauge based on your measurements

    1. Go / No-Go gauges are inspection tools to quickly check the dimension of a part. A dimension can not always be perfect, so there is a tolerance window. The go feature prevents any dimension that is too big, and the no-go feature prevents any dimensions that is too small.

      1. Example: The nominal length of a part is 1in with a tolerance of 0.1in. That means its tolerance window allows for lengths less than 1.1in and greater than 0.9in.

      2. Go feature: Should allow lengths less than 1.1in to go through, and captures any lengths greater than 1.1 in

      3. No-Go feature: Should not allow lengths less than 0.9in to go through, but should allow, and captures any lengths less than 0.9in

  6. Create a technical drawing with critical dimensions clearly defined.

    1. Critical dimensions are bubbled

  7. Fabricate the Go/No-Go gauge (3D print, hand made, or machined).

  8. Verify the tool by comparing the critical dimensions against the technical drawing.

  9. [Optional] Compare efficiency: Measure the time it takes to inspect nuts with calipers vs. using the tool -

    1. Will show measurable results which you can put in your resume or portfolio

  10. [Optional] 3D print something like a vertebrae to demonstrate fitment.

    1. Will have a photo that looks cool

RESULTS

David Oh