Post on 07-Sep-2018
transcript
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