Introduction to Dimensioning and Tolerancing Dr. Darrell Wallace

2 General Guidelines for Dimensioning and Multiple Views Show dimensions in the most logical view Don’t dimension to hidden lines. If necessary, use section views. Know the difference between first angle and third angle projections and how they are interpreted.

3 Normal Placement Placement in Limited Space Placement of Dimensions

4 Dimensioning Circles and Arcs Simple Cylinder Stepped Shaft

5 Dimensioning Radii

6 Dimensioning Holes

7 Counterbores and Countersinks Counterbores Countersinks

8 Dimensioning Angles Angles can be dimensioned using either linear or angular dimensions.

9 Dimensioning Equally Spaced Holes

10 Specifying Hole Dimensions

11 Dimensioning Hole Positions Whenever possible, good drawing practice dictates that dimensions should be placed in a view that shows the dimensioned feature visibly (without hidden lines).

12 Tabular Dimensions

13 Ordinate Dimensioning

14 Part Family Dimensioning

15 Decimal and Fractional Dimensions English Fractional Units are Based on Dividing Larger Units in Half 1”/2 = ½” ½”/2=1/4” … 1/8”, 1/16”, 1/32”, 1/64” Fractional to Decimal Conversions 1” = ”1/16” = ” ½” = ”1/32” = ” ¼” = /64” = ” 1/8” = ”1/128” = ”

16 English vs. Metric Units Within the metric system: 1 m = 100 cm = 1000 mm.01 m = 1 cm = 100 mm.001 m =.1 cm = 1 mm 1  (micron) =.001 mm = m English to Metric 1 mile = km 1 yd =.9144 m 1 in = 2.54 cm = 25.4 mm in =.0254 mm = 25.4  Metric to English 1 km = mile 1 m = yd = 39.4 in 1 cm = in 1 mm = in

17 Tolerances ALL dimensions used to define the shape and size of a part MUST have an associated tolerance Sometimes tolerances are controlled by default or “general” tolerances that apply to the entire drawing. Tolerances that are too “loose” make for parts that don’t fit or function properly. Tolerances that are too “tight” make parts unnecessarily expensive.

18 Tolerance Types Limit Tolerance Plus / Minus Tolerance Bilateral Unequal bilateral Unilateral Choice of tolerances and dimensioning schemes should be based on functional dimensioning

19 Dimensional Precision The dimensional precision implies (to some degree) what the tolerance should be: Fractional± 1/32”(carpentry) X.X± 0.10(hacksaw) X.XX±0.010(standard machining) X.XXX±0.001(careful machining) X.XXXX±0.0001(grinding) X.XXXXX……(polishing, specialty processes)

20 Process Capabilities Though it is generally not recommended that you specify processes on your drawings, it is a good idea to keep in mind the costs and capabilities of the processes that will likely be used.

21 The Costs of Precision

22 Title Block, BOM, and Revisions A.Title Block B.Bill of Materials C.Revision Block