Chapter4 Tolerance Rules 公差原则 T T T T eeee rrrr mmmm ssss 术术术术 语语语语 T T T T oooo llll eeee rrrr aaaa nnnn cccc eeee R R R R uuuu llll eeee ssss 公公公公 差差差差 原原原原 则则则则 P P P P rrrr iiii nnnn cccc iiii pppp llll eeee o o o o ffff I I I I nnnn dddd eeee pppp eeee nnnn dddd eeee nnnn cccc yyyy 独独独独 立立立立 原原原原 则则则则 E E E E nnnn vvvv eeee llll oooo pppp eeee R R R R eeee qqqq uuuu iiii rrrr eeee mmmm eeee nnnn tttt 包包包包 容容容容 要要要要 求求求求 M M M M aaaa xxxx iiii mmmm uuuu mmmm M M M M aaaa tttt eeee rrrr iiii aaaa llll P P P P rrrr iiii nnnn cccc iiii pppp llll eeee 最最最最 大大大大 实实实实 体体体体 原原原原 则则则则

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