Metrology Flashcards
Metrology
Measuring dimensions
Accuracy
Degree of agreement between measured dimensions
Precision
Degree instrument gives repeated measurements
Resolution
Smallest dimension instrument can read
Sensitivity
Smallest difference in dimensions instrument can detect
Calibration
Recursive process, calibrate with another calibrated instrument
Surface plate
Horizontal reference plane
Non-magnetic
No thermal expansion
Wear resistant
Usually granite
Surface plate grades
AA: Lab grade, controlled atmospheres, very precise
A: Inspection grade
B: Toolroom grade, used for production work in shops
Dial indicators
Plunger-type indicators used for surface measurements
Test indicators
Lever-type indicators used for surface measurements at smaller scale than dial indicators
Telescoping gages
Used to determine internal diameter of a hole
Gage blocks/Joe blocks/Slip gages
Precision ground rectangular blocks used to calibrate shop tools
Coordinate measuring machines (CMM)
Either 3 or 5 axes, very high sensitivity
Plug gages
Gages with external measuring surface that checks thread/hole size (go/nogo)
Ring gages
Gages for checking the external diameter of a cylindrical object
Snap gages
Gages to verify an outside dimension, if it fits in the gage’s gap, then you’re good
Unilateral tolerance
Tolerance has unequal magnitude in each direction
Bilateral tolerance
Tolerance has equal magnitude in each direction
Maximum material condition (MMC)
The dimensions that allow for the largest part volume (smaller holes, larger shafts, etc)
Least material condition (LMC)
The dimensions that allow for the smallest part volume (larger holes, smaller shafts, etc)
Clearance fit
Mating surfaces have a gap between them
Allowance > 0
Interference fit
Mating surfaces overlap each other
Allowance < 0
Line fit
No gap or overlap between mating surfaces, the fit exactly
Allowance = 0
Allowance
Smallest hole minus largest shaft
