Introduction to Engineering Tolerancing - 2

1
Introduction to EngineeringTolerancing - 2

• Agenda
• Determining limits
• Use standard tables for tolerancing and control
  fit

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How to Determine Limits

• Now you can calculate tolerances, given the max
  and min limits on a dimension
• How does a design engineer know what limits to
  use?
• First, decide what type of fit you want.
• Then, use a table.

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Standard Precision Fits English Units

• Running and sliding fits (SC)
• Clearance locational fits (LC)
• Transition locational fits (LT)
• Interference locational fits (LN)
• Force and shrink fits (FN)
• See Tables in the Appendix

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Example What are tolerance limits for a Nominal
½ shaft with RC2 fit?
Hole Max .5004 Min .5000
Shaft Max .49975 Min .49945
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Metric Limits and Fits

• Based on Standard Basic Sizes ISO Standard, see
  Appendix material
• Nominal Size Basic Size
• Symbols and Their Definitions

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Metric Preferred Hole Basis System of Fits
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Metric Tolerance Example - Nominal 6 mm Hole and
Shaft with Close Running Fit 6 H8/f7
Shaft
Hole
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Basic System

• Clearance Gap Fill
• Fill Fill1 Fill2
• Cmax Gmax Fmin
• Cmin Gmin Fmax
• Both Cmax and Cmin gt0 Clearance fit
• Both Cmax and Cmin lt0 Interference fit
• Cmax gt 0 Cmin lt 0 Transition fit
• System Tolerance Cmax - Cmin

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Gap and Fill Clearance Example
Clearance Gap Fill
Cmax Gmax Fmin
Cmax 1.248 - .500 - .750 -.002
Cmin
Cmin
What is Type of Fit?
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Assignment

• Dwg 8 Tolerance and Fits Worksheet