FEAR
Our greatest fear is not that we are inadequate,but that we are powerful beyond measure.
It is our light, not our darkness, that frightens us.We ask ourselves, Who am I to be brilliant,gorgeous, handsome, talented and fabulous?
Your playing small does not serve the world.There is nothing enlightened about shrinking
so that other people won't feel insecure around you.
~Quoted selectively from Marianne Williamson and Nelson Mandela
Tolerances, Limits and Fits
A succession of rude jokes
Tolerances, Limits and Fits
The Importance of Fitting In
Tolerances
• A convention to define leeway in manufacturing
Limits
• Maximum Thresholds that may not be exceeded in manufacture
Fits
• The manner in which items fit together, and the behaviour of this
Why Tolerances?
• No dimension can be “accurately machined”
• Thermal instability of material
• Greater accuracy requires more precision tooling and time, which is costly
• Function of fit must be considered
Conventions of Notation
Further Conventions of Notation
Conventions
• Nominal size is the “actual” vernier sizeWe tend to base our calculations on the hole size – tooling
• Capital ‘H’ refers to holes
• Lower case letters a to z refer to shaft
• Numbers refer to magnitude of displacement from nominal
Types Of Fits
• Clearance fit - A fit provides a clearance. The tolerance zone of the hole is entirely above that of the shaft.
• Transition fit - A fit provides either a clearance or an interference. The tolerance zones of the hole and the shaft overlaps.
• Interference fit - A fit provides an interference. The tolerance zone of the hole is entirely below that of the shaft.
• Source: Hong Kong University of Science and Technology
The MicrometreMeasured with a micrometer
Item
Anthrax Spore 6 μm
Diameter of Bacterium 1 - 10 μm
Discernable Gap 20 μm
Human Hair 70 μm
Sheet of Paper / Coat of paint 100 μm
Tolerance:
• Nominal : 48mm
• H8 f7
CalculationNominal Plus Minus
Hole 48 39 -25
Shaft 48 +0 -50
48+.039(-)0
48 - .025 - .050
Hole
Shaft
48+.039(-)0
48 -0.025-0.050
