10 Tolerancing

Define terms related to tolerancing. Explain how tolerances are expressed on a drawing. Identify tolerance values for dimensions on the drawing, regardless of the tolerancing expression. Compare customary inch tolerance classes with metric tolerance classes. Calculate tolerances or limits for mating parts based on maximum material conditions and allowance.

Tolerancing Defined Tolerance is the total amount by which a dimension can vary Expressed as: Bilateral Unilateral Limits

Tolerancing Defined In each of these examples, the tolerance is .008

Tolerancing Applied Tolerances can be applied to both location and size dimensions

Tolerancing Concepts Basic hole system: system for calculating the limits of a hole-shaft relationship Maximum material condition: condition of a feature wherein the most material is present Least material condition: condition of a feature wherein the least material is present Allowance: tightest fit of two parts calculated by comparing maximum material conditions

Datum Identification A datum may be represented by a surface, center plane, or an axis

Dimension Origin Symbol

American Standard Tolerances Classifications for ASME fits: Running or sliding clearance fits (RC) Locational clearance fits (LC) Transitional clearance or interference fits (LT) Locational interference fits (LN) Force or shrink fits (FN)

Metric Tolerances and Fits Classifications for metric fits:

What is the difference between tolerance and limits? Tolerance is the total amount by which a dimension can vary. Limits are the extreme maximum and minimum dimensions allowed by the tolerance.

What is the difference between a unilateral tolerance and a bilateral tolerance? A unilateral tolerance varies from the dimensional value in one direction only (either plus or minus). A bidirectional tolerance varies from the dimensional value in both plus and minus directions.

What are the two basic ways in which tolerances are expressed on the dimensions of a drawing? Plus-and-minus dimensioning and limit dimensioning (may also be expressed as a general tolerance in the tolerance block).

If a dimension is 2.235 .005, what is the tolerance? .010

How does the metric system of tolerances and fits differ from the American system? The concept is the same between the two systems, but different notation is used.

If a hole is . 187+. 002/–. 000 and a shaft is . 187+. 000/– If a hole is  .187+.002/–.000 and a shaft is  .187+.000/–.003, what is the allowance? .000