Tolerances are the allowable deviation in size, location, and geometry of a feature.
The primary role of dimensioning is to control the size or location of a feature.
Every dimension has to have a tolerance associated with it: X.XX±0.02
Does not control for the form (geometry) of the feature directly, it only controls the size or location
Size of a feature at one end of its tolerance zone where there is the most amount of material.
Size of a feature at one end of its tolerance zone where there is the least amount of material.
Tolerances always add!
0.7±0.2 + 0.5±0.3 = 1.2±0.5
0.7±0.2 - 0.5±0.3 = 0.2±0.5
An assembly of two parts creates a "fit" whose functional characteristic is determined by the differences in the parts' associate sizes.
The MMC of the hole is always greater than the MMC of the shaft: MMChole > MMCshaft
Both the MMC and the LMC of the hole are less than the MMC and LMC of the shaft, respectively
MMChole < MMCshaft
LMChole < LMCshaft
Minimum hole size is the basic size
Minimum shaft size is the basic size
The loosest fits. Used when shaft must move freely in a hole. Always has clearance, position is not critical.
Tighter than RC. Shaft and hole may be same size (line-to-line fit). Location is more important than RC.
Transition between LC and LN. May have slight clearance or may have slight interference.
Can be line-to-line, but almost always shaft is larger than the hole. Position/location very important.
Pure interference fits. Used to secure parts together.
Theoretical nominal size to which the tolerance limits are applied.
Smallest hole is set as the basic size. Most common due to drill tooling
Largest diameter of the shaft is assigned as the basic size. Less popular.