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Dimensional inspection and tolerances · Lesson 3 of 4

Dimensional inspection and tolerances: methods and worked application

The inspection sequence, what to do when a reading is out of band, tool technique, and five worked checks with their arithmetic.

You will be able to: Inspect a formed piece in a fixed order, use the micrometer, caliper and tape correctly, and work thickness, Blank Width, stack-up and piece-count checks with every input stated.

13 min · 12 slides · 10 questions

All lessons in this module
Slide 1 of 12

The inspection sequence

Work in the same order every time:

  • Read the order
  • Confirm material, gauge and finish
  • Zero the tools
  • Thickness, in three places
  • Each leg, to the mold line
  • Each angle and its direction
  • Hems: end, face, return, gap
  • Blank Width
  • Painted side
  • Length and piece count
  • Flatness and surface
  • Record and initial
The inspection sequence and the out-of-band loopTwelve numbered steps in a column: read the order; material, gauge and finish; zero the tools; thickness three times; each leg; angles and direction; hems; Blank Width; painted side; length and count; flatness and surface; record and initial. Beside them, the loop after each check: in band, go on to the next check; not in band, re-zero, clean and re-measure; back in band, go on to the next check; still out, hold the piece and flag it, never fix by eye.123456789101112Read the orderMaterial, gauge, finishZero the toolsThickness, 3 placesEach legAngles + directionHemsBlank WidthPainted sideLength + countFlatness, surfaceRecord + initialAfter each checkIn band?Still out?YesNoNoYesRe-zero, clean,re-measureNext checkHOLD + flagnever fix by eye

Twelve numbered steps in a column, from reading the order to recording and initialling. Beside them, the loop after each check: in band, go on to the next check; out of band, re-zero and re-measure; back in band, go on to the next check; still out, hold the piece and flag it. Both pass branches end on a Next check terminal, not on a particular step.

1
Read the order
2
Confirm material, gauge and finish
3
Zero every tool (Mitutoyo guidance)
4
Thickness, in three places
5
Each leg, to the mold line
6
Each bend angle and its direction
7
Hems: end, face, return and gap
8
Blank Width
9
Painted side
10
Length (120 in standard, 126 in max) and piece count
11
Flatness and surface
12
Record each reading with its tool and zero check, and initial
This module's method. The order and the project specification decide acceptance; the bench holds and flags, it never fixes by eye.

Sources

Videos for this lesson

What this video shows: Mitutoyo's product demonstration of digital caliper use, the tool for short legs, hem returns and hem gaps.

Video: How To Use A Mitutoyo Digital Caliper by Mitutoyo America Corporation, on YouTube. Chosen from the video's published description.

What this video shows: Mitutoyo's product demonstration of digital micrometer use, the tool for sheet thickness checks.

Video: How To Use A Digital Micrometer From Mitutoyo by Mitutoyo America Corporation, on YouTube. Chosen from the video's published description.

Glossary

Ratchet stop
A micrometer's constant-force device; Mitutoyo says to always use it.
Parallax
A reading error from looking at a scale at an angle; read square to the line.
Worst-case stack-up
The sum of all the tolerances in a chain of dimensions.
RSS stack-up
The square root of the sum of the squared tolerances, which assumes independent, centred errors.
Hold
This module's term: setting a piece aside, flagged, when a reading stays out of band after re-zeroing and re-measuring.