Understanding Tolerancing: Definition, Importance, and Specification, Slides of Computer Graphics and Animation

Download Understanding Tolerancing: Definition, Importance, and Specification and more Slides Computer Graphics and Animation in PDF only on Docsity!

Tolerancing

Objective

• To learn how to effectively tolerance parts

such that parts function correctly and cost is

kept to a minimum

Functionality

• Assemblies: Parts will often not fit together if their

dimensions do not fall with in a certain range of

values

• Interchangeability: If a replacement part is used it

must be a duplicate of of the original part within

certain limits of deviation

• The relationship between functionality and size or

shape of an object varies from part to part

• the usefulness of eyeglasses is extremely sensitive to size and shape
• the usefulness of glass marbles are not very sensitive to size and shape

Cost

• Cost generally increases with smaller tolerance
  • There is generally a lower limit to this relationship where larger tolerances do not affect cost (0.020 Vs 0.010)
  • Small tolerances cause an exponential increase in cost
• Parts with small tolerances often require special

methods of manufacturing

• Parts with small tolerances often require greater

inspection and call for the rejection of parts

• Do not specify a smaller tolerance than is necessary!

General Tolerances

• A note may be placed on the drawing which specifies

the tolerance for all dimensions except where

individually specified

• ALL DECIMAL DIMENSIONS TO BE HELD TO 0.
• Several tolerances may be specified for dimensions

with a different number of decimal places or for a

different type of dimension such as angles

• Specific tolerances given to a dimension on a drawing

always supersede general tolerances

Specific Tolerances

• The tolerance for a single dimension may be

specified with the dimension

• The tolerance is total variation between the upper and lower limits (tolerance = .020)

• Limits

• Unilateral tolerance

• Bilateral tolerance

Tolerancing Holes and Shafts

• Types of Fit
  • Clearance fit
    • The parts are toleranced such that the largest shaft is smaller than the smallest hole
    • The allowance is positive and greater than zero
  • Transition fit
    • The parts are toleranced such that the allowance is negative and the max. clearance is positive
    • The parts may be loose or forced together
  • Interference fit
    • The max. clearance is always negative
    • The parts must always be forced together

Tolerancing Holes and Shafts

• Preferred fits: A specified system of fits for

holes and shafts for SI units

• Hole basis
  • The minimum hole size equals the basic hole size
  • Uses the symbol “H” in the tolerance specification
• Shaft basis
  • The maximum shaft size equals the basic shaft size
  • Uses the symbol “h” in the tolerance specification

Examples: Holes and Shafts

• Metric

• Fit 6 H7/n
  • Metric: Preferred Hole Basis (H)
  • Allowance: -0.
  • Max. Clearance: 0.
  • Hole Limits: 6.012 / 6.
  • Shaft Limits: 6.016 / 6.
  • Hole Tolerance: 0.
  • Shaft Tolerance: 0.
  • Type of fit: Transition

Examples: Holes and Shafts

• Metric

• Fit 6 C11/h
  • Metric: Preferred Shaft Basis (h)
  • Allowance: 0.
  • Max. Clearance: 0.
  • Hole Limits: 6.145 / 6.
  • Shaft Limits: 6.000 / 5.
  • Hole Tolerance: 0.
  • Shaft Tolerance: 0.
  • Type of fit: Clearance

Example

• Part A fits into part B

• All dimensions for part A are held 0.

• Specify the dimensions and tolerance for B

with an allowance of 0.

Example

• Solution with allowance of.

Part A

Part B

Example

• Allowance equals 0.

• Specify dimensions and tolerance for part B