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Precision Dimensioning

Precision Dimensioning. Engineering II. Dimensioning Rectangular Prisms. Dimensioning Cylinders. The diameter of cylinders should be dimensioned in the rectangular view (not the circular view). Cylinders without a hole passing through them only require one view. Dimensioning Cones.

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Precision Dimensioning

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  1. Precision Dimensioning Engineering II

  2. Dimensioning Rectangular Prisms

  3. Dimensioning Cylinders • The diameter of cylinders should be dimensioned in the rectangular view (not the circular view). • Cylinders without a hole passing through them only require one view.

  4. Dimensioning Cones

  5. Dimensioning Spheres

  6. Rectangular Coordinate Dimensioning • Used when computer-controlled production machines are used to manufacture parts. • The designer should consult with personnel in manufacturing to ensure that the origin is located in an appropriate position. • Two types of rectangular coordinate dimensioning: • Coordinate Dimensioning with Dimension Lines • Coordinate Dimensioning Without Dimension Lines

  7. Coordinate Dimensioning with Dimension Lines

  8. Coordinate Dimensioning without Dimension Lines

  9. Tabular Dimensioning • Tabular dimensioning is used when a series of parts consists of the same features or geometry but vary in dimension. • Letters are used in place of dimension values, and the values are then placed in a table. • Most standard parts are dimensioned this way in catalogs, the machinery handbook, and in the back of most textbooks.

  10. Tabular Dimensioning

  11. Dual Dimensioning – Position Method • Millimeter value is placed above (or below) the inch value or separated by a dash.

  12. Dual Dimensioning – Bracket Method • Millimeter value is enclosed in square brackets. A note should be placed on the drawing such as: DIMENSIONS IN [ ] ARE MILLIMETERS.

  13. Tolerance Dimensioning • Why do we need tolerance dimensioning? • Interchangeable parts manufacturing • Parts are manufactured at widely separate localities • Effective size control • Modern industry relies on it for subcontracting and replacement parts • Accuracy is Expensive, however

  14. Reading Dimensions

  15. Specification of Tolerances Limit Dimension Bilateral-Equal Unilateral Bilateral-Unequal

  16. Tolerance • Tolerance is the total amount a specific dimension is permitted to vary (difference between the maximum and minimum limits). • The dimension below has a tolerance of .0003.

  17. Maximum Material Condition • When specifying tolerance dimensions, the maximum material condition (MMC) means the product or part contains the maximum amount of material specified by the tolerance. • The heaviest part.

  18. Maximum Material Condition • For the part shown here the MMC is 1.4996 since that size would yield the most material.

  19. Allowance • Allowance is the minimum clearance or maximum interference intended between the maximum material condition (MMC) of mating parts. • The allowance for the system below is: 25.000 - 24.890 = 0.110

  20. More Terminology • Nominal Size - General identification in fractions (ex. 1-1/2 for 1.500). • Basic Size - General identification in decimal (ex. 1.500). • Actual Size - Measured size. • Limits - Maximum and minimum sizes indicated by the tolerance dimensions.

  21. Clearance Fit • Space is always left between parts. • What is the allowance in this case? • 1.5000 – 1.4988 = .0012

  22. Interference Fit • Always an interference of material. • What is the allowance in this case? • 1.5000 – 1.5013 = -.0013 or just .0013

  23. Transition Fit • Fit might result in clearance or interference.

  24. Line Fit • Clearance or surface contact may result at assembly.

  25. Basic Hole System (Hole Basis) • The minimum size hole is taken as the basic size.  • Used when standard tools are used to produce holes (reamers & broaches).

  26. Basic Shaft System (Shaft Basis) • The maximum shaft size is taken as the basic size.  • When several parts having different fits, but one nominal size are required on a single shaft.

  27. Specifying a Fit - Inches • Determine type of fit and find corresponding table • Determine basic size • Find size range on table • Determine tolerances for Hole and Shaft • Remember values are in thousandths of an inch.

  28. Specifying a Fit - Inches • RC1 - Close Sliding Fit • Basic size of 1.500 • Upper tolerance on hole is +0.4, which is really +0.0004 • Lower tolerance on hole is -0. • Upper tolerance on shaft is -0.0004 • Lower tolerance on shaft is -0.0007

  29. Specifying a Fit - Inches

  30. Specifying Fits - Metric • Determine type of fit and find corresponding table • Determine basic size • Find size range on table • Determine tolerances for Hole and Shaft

  31. Specifying Fits - Metric • Loose Running Fit • Basic size of 25

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