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QUICK FACT GUIDES FOR MACHINISTS
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GUIDES
FUNDAMENTALS OF
DRILLING & TAPPING
FUNDAMENTALS
OF THREADING ON A LATHE
FUNDAMENTALS OF
WORKING BETWEEN CENTERS FUNDAMENTALS OF HEAT TREATING
FUNDAMENTALS
OF MILLING
FUNDAMENTALS
OF SAWING
METALWORKING
SHOP TERMS
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DIMENSIONING TERMS: ACTUAL SIZE: An
actual size is a measured size. ANGULARITY: Is
the condition of a surface or line which is at the specified angle (other than
90 degrees) from a datum plane or axis. An angularity tolerance for a surface
specifies a tolerance zone confined by two parallel planes, inclined at the
specified angle to a datum plane, within which the tolerance surface must lie.
ALLOWANCE:
An allowance is an intentional difference between the maximum material limits of
mating parts, it is the minimum clearance (positive allowance) or the maximum
interference (negative allowance) between such parts. BASIC SIZE: The
basic size is that size from which the limits of size are derived by the
application of allowances and tolerances. BASIC DIMENSION:
A dimension specified on a drawing as BASIC is a theoretical value used to
describe the exact size, shape, or location of a feature. It is used as a basis
from which permissible variations are established by tolerances on other
dimensions or in notes. BILATERAL TOLERANCE:
A bilateral tolerance is a tolerance in which variation is permitted in both
directions from the specified dimension. CIRCULAR RUNOUT:
Is the maximum permissible surface variation at any fixed point during one
complete rotation of the part about the datum axis. CLEARANCE FIT:
A clearance fit is one having limits of size so prescribed that a clearance
always results when mating parts are assembled. CONCENTRICITY:
Is the condition of surfaces of revolution wherein they have a common axis. COORDINATE DIMENSIONING: A system of assigning dimensions based on a common starting point. CYLINDRICITY:
Is a condition of a surface of revolution in which all elements form a cylinder.
A cylindricity tolerance specifies a tolerance zone confined to the annual space
between two concentric cylinders within which the surface must lie. FIT: Fit
is the general term used to signify the range of tightness or looseness which
may result from the application of a specific combination of allowances and
tolerances in the design of mating parts. Fits are of four general types:
Clearance, Interference, Transition and Line. DATUMS: Datums
are points, lines, planes, cylinders, etc., assumed to be exact for the purpose
of computation from which the location of geometric relationship (form) of
features of a part may be established. DIMENSIONS:
A dimension is a numerical value expressed in appropriate units of measure and
indicated on a drawing along with lines, symbols, and notes, to define a
geometrical characteristic of an object. FEATURE: Features
are specific characteristics or component portions of a part and may include one
or more surfaces such as holes, screw threads, profiles, or faces. FLATNESS: Is
the condition of a surface having all elements of a surface in one plane. A
flatness tolerance specifies a tolerance zone confined by two parallel planes
within which the surface must lie. GEOMETRIC FORM: Geometric
form refers to the various geometric forms, such as a plane, cylinder, cone,
square or a hexagon. INTERFERENCE FIT: An interference fit
is one having limits of size so prescribed that an interference always results
when mating parts are assembled. LINE FIT:
A line fit is one having limits of size so prescribed that surface contact or
clearance may result when mating parts are assembled. MAXIMUM MATERIAL CONDITION (MMC): The condition where the feature contains the maximum amount of material
e.g. minimum hole diameter and maximum shaft size. NOMINAL SIZE: The
nominal size is the designation which is used for the purpose of general
identification e.g. 3/8" drill, 0.062 stock size, etc. PARALLELISM: Is
the condition of a surface or line which is equidistant at all points from a
datum or axis. A parallelism tolerance specifies one of the following: 1. A tolerance zone confined by two planes
parallel to a datum plane within which the considered feature (axis or surface)
must lie. 2. A cylindrical tolerance zone confined by two parallel planes
perpendicular to a datum plane within which the median plane or a feature must
lie. PERPENDICULARITY:
Is the condition of surfaces, axis, or lines which are at right angles to each
other. A perpendicularity tolerance specifies one of the following: 1. A tolerance zone confined by two parallel
planes perpendicular to a datum plane within which the surface of a feature must
lie. 2. A tolerance zone confined by two parallel
planes perpendicular to a datum plane within which the medium plane of a feature
must lie. 3. A tolerance zone confined by two parallel planes perpendicular
to a datum axis within which the axis of a feature must lie. 4. A cylindrical tolerance zone perpendicular
to a datum plane within which the axis of a feature must lie. 5. A tolerance zone confined by two parallel,
straight lines perpendicular to a datum plane or datum axis within which the
element of the surface must lie. Note: That the
perpendicularity tolerance applied to a plane surface controls flatness if a
flatness tolerance is not specified. REFERENCED DIMENSION:
A referenced dimension is a dimension usually without tolerances used only for
informational purposes and does not govern production or inspection operations. REGARDLESS OF FEATURE SIZE (RFS): The condition where tolerance of position or form must be met
irrespective of where the feature lies within its size tolerance. ROUNDNESS: Is
a condition of a surface of revolution such as a cylinder, cone, or sphere,
where all points of the surface intersected by any plane, perpendicular to a
common axis (cylinder, cone), passing through a common center (sphere), are
equidistant from the axis. A roundness tolerance specifies a tolerance zone
bounded by two concentric circles in that plane within which the periphery must
lie. STRAIGHTNESS:
Is the condition where an element of a surface is a straight line. A
straightness tolerance specifies a tolerance zone of uniform width along a
straight line, within which all points of the considered line must lie. SYMMETRY:
Is a condition where a part or a feature has the same contour and size on
opposite sides of a central plane, or a condition in which a feature is
symmetrically disposed about the central plane or a datum feature. TOLERANCE: (1)
Tolerance is the amount of variation permitted on dimensions or surfaces of
machine parts. The tolerance is equal to the difference between the maximum and
minimum limits of any specified dimension. For example, if the maximum limit for
the diameter of a shaft is 2.000 inches and its minimum limit is 1.990 inches,
the tolerance for this diameter is 0.010 inch. 2. No element of the actual feature shall
extend beyond the envelope of perfect form at MMC. This envelope is the form
implied by the drawings. 3. The measured dimensions of the feature at any cross section shall not
be less than the minimum limit of size of an external feature nor grater then
the maximum limit of size of an internal feature. TRANSITION FIT:
A transition fit is one having limits of size so prescribed that either a
clearance or an interference may result when mating parts are assembled. TRUE POSITION TOLERANCE: True position denotes the basic or theoretically exact position. UNILATERAL TOLERANCE: A
unilateral tolerance is a tolerance in which variation is permitted in only one
direction from the specified dimension. |
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Copyright © 2002 QUICK FACT GUIDES FOR MACHINISTS
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