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Chapter4 Chapter4 Tolerance RulesTolerance Rules 公差原则公差原则

4.1 Terms4.1 Terms术语术语4.2 Tolerance Rules4.2 Tolerance Rules 公差原则公差原则 4.2.1 Principle of Independency4.2.1 Principle of Independency独立原则独立原则4.2.2 Envelope Requirement4.2.2 Envelope Requirement包容要求包容要求4.2.3 Maximum Material Principle4.2.3 Maximum Material Principle最大实体原则最大实体原则

4.1 Terms术语• Actual Local Size (Da, da) : is the value of any individual distance at

any cross section of a size feature.

• The actual local size is a two-point measurement, taken with an instrument like a caliper or micrometer, which is checked at a point along the cross section of the part. A feature of size may have several different values of actual local size.

• Actual Mating Envelope (dfe): is defined according to the type of size feature being considered. The actual mating envelope of shaft is similar perfect feature counterpart of the smallest size that can be circumscribed about the feature so it just contacts the surfaces at the highest points.

• The actual mating envelope of a hole Dfe can be calculated as

• Virtual Condition (VC): is the theoretical extreme boundary of a size feature generated by the collective effects of MMC (the maximum material principle) and any applicable geometric tolerances.

• Worst-Case Boundary (WCB): is a general term to refer to the extreme boundary of a size feature that is the worst-case for assembly. Depending upon the part dimensioning, a worst-case boundary can be a virtual condition, inner boundary, or outer boundary.

• Inner Boundary (IB): is a worst-case boundary generated by the smallest size feature minus the stated form or position tolerance.

• Outer Boundary (OB): is a worst-case boundary generated by the largest feature size plus the stated form or position tolerance.

4.2 Tolerance Rules

4.2.1 Principle of Independency

Example1

4.2.2 Envelope Requirement

Example2

4.2.3 Maximum Material Principle

Example3