tolerances-w-solutions

# tolerances-w-solutions - ME250 Design and Manufacturing I...

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Tolerances ME250 Design and Manufacturing I

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2 Outline What? Why? Dimensional Tolerances Geometric Tolerances Tolerance Selection Summary
3 What?

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4 What? Dimensional tolerances Specifies allowable variations in length, diameters, and radii Given as numerical limits We cover in me250 Geometric tolerances Specifies allowable variations in non-dimensional geometric characteristics straightness, flatness, roundness, cylindricity, etc. Given as feature control frame (FCF) We cover briefly in me250
5 Why? To assure interchangeability of mass-produced parts It is impossible to manufacture exactly the same parts every time (more in statistics lecture). Variations in each part shape must be within certain limits (= tolerances) in order to function properly.

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6 Dimensional Tolerances Types of dimensional tolerances Limit Dimensions Plus or Minus Tolerances Page or Block Tolerances
7 Dimensional Tolerances Limit Dimensions Minimum and maximum allowable dimensional values For external dimensions (“shaft”): For internal dimensions (“hole”):

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8 Dimensional Tolerances Plus or Minus Tolerances Basic size and allowable maximum upper and lower deviations Page or Block Tolerances General note that applies to all dimensions not covered by other tolerancing type or 10.0 ± 0.1
9 Dimensional Tolerances Inch tolerance definitions (ANSI) Limits: The maximum and minimum size that the part is allowed to be. Basic (nominal) size: The size from which the limits are calculated. Tolerance: The total amount a specific dimension is permitted to vary ** . Maximum Material Condition (MMC): The size of the part when it consists of the most material. Least Material Condition (LMC): The size of the part when it consists of the least material ** also common: ½ of the allowable variation if given in symmetric bilateral tolerance format (the convention adopted in the statistics lecture).

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10 Dimensional Tolerances Exercise: Fill in the table Shaft Hole Limits Basic Size Tolerance MMC LMC Common for hole and shaft and is the closest fraction if unspecified.
11 Dimensional Tolerances Solution Shaft Hole Limits Basic Size Tolerance MMC LMC .51, .47 .49, .50 .04 .01 .51 .49 .47 .50 Common for hole and shaft and is the closest fraction if unspecified.

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12 Dimensional Tolerances Inch limits and fits definitions (ANSI) Maximum Clearance: The maximum amount of space that can exist between the hole and the shaft. Max. Clearance = LMC hole LMC shaft Minimum Clearance (Allowance): The minimum amount of space that can exist between the hole and the shaft. Min. Clearance = MMC hole MMC shaft
13 Dimensional Tolerances Exercise: Fill in the table Max. Clearance Min. Clearance

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14 Dimensional Tolerances Solution Max. Clearance Min. Clearance .50 - .47 = .03 .49 - .51 = -.02 What does a negative clearance mean?
15 Dimensional Tolerances Major types of fits Clearance Fit There is always a space Min. Clearance > 0 Interference Fit There is never a space.

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## This note was uploaded on 09/12/2011 for the course MECHENG 250 taught by Professor Stevis during the Winter '09 term at University of Michigan.

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tolerances-w-solutions - ME250 Design and Manufacturing I...

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