In
precision mechanics
Precision mechanics (also "fine mechanics") is an engineering discipline that deals with the design and construction of smaller precision machines, often including measuring and control mechanisms of different kinds.
The study may be further defin ...
, fit refers to the degree of 'looseness' with which a
shaft
Shaft may refer to:
Rotating machine elements
* Shaft (mechanical engineering), a rotating machine element used to transmit power
* Line shaft, a power transmission system
* Drive shaft, a shaft for transferring torque
* Axle, a shaft around whi ...
is inserted into a
bored
In conventional usage, boredom, ennui, or tedium is an emotional and occasionally psychological state experienced when an individual is left without anything in particular to do, is listlessness and dissatisfaction arising from a lack of occup ...
hole.
This coupling is related to the
tolerance
Tolerance or toleration is the state of tolerating, or putting up with, conditionally.
Economics, business, and politics
* Toleration Party, a historic political party active in Connecticut
* Tolerant Systems, the former name of Veritas Software ...
or allowance of both parts' dimensions. The shaft and the orifice must be of a similar diameter, otherwise there will not be a correct adjustment. With this in mind, measurements have been internationally standardised according to
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
regulation to ensure the
interchangeability of items and their mass production.
Tolerance values are designated with a capital letter in the case of orifices and lower case letters in the case of shafts. The lower the value the higher the
machining
Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...
costs, as a greater precision is required.
Maximum and minimum clearance
The maximum clearance of a fit is the difference between the
upper bound of the orifice diameter and the
lower bound
In mathematics, particularly in order theory, an upper bound or majorant of a subset of some preordered set is an element of that is greater than or equal to every element of .
Dually, a lower bound or minorant of is defined to be an element ...
of the shaft diameter.
: maximum clearance = maximum orifice diameter – minimum shaft diameter
The minimum clearance meanwhile is the difference between the lower bound of the orifice diameter and the upper bound of the shaft diameter.
: minimum clearance = minimum orifice diameter – maximum shaft diameter
The maximum clearance in a loose or sliding fit is always greater than zero; on the other hand, in a tight fit both the maximum and minimum clearance are negative.
See also
*
Engineering fit
Engineering fits are generally used as part of geometric dimensioning and tolerancing when a part or assembly is designed. In engineering terms, the "fit" is the clearance between two mating parts, and the size of this clearance determines whethe ...
*
Interference fit
Bibliography
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Mechanics