function of geometric tolerance is to explain the engineering objective of
components and assemblies. The datum reference frame can explain how the part.
Tolerance can accurately define the dimensional needs for a part, permitting
over 50% more tolerance than coordinate dimensioning in a few cases. Suitable
purpose of tolerance will confirm that the part described on the drawing has
the preferred form, fit and purpose with the highest possible tolerances
1. Fundamental rules for Geometric Tolerance
dimensions should have a tolerance. Each attribute on every manufactured
component is subject to change; hence, the limits of acceptable difference must
be defined. Plus and minus tolerances
may be used to dimensions from a common tolerance block.
describe the geometry and allowable change. Measurement and scaling of the
drawing is not permitted excluding in certain cases.
drawings describe the necessities of completed parts. Each dimension and
tolerance needed to define the completed part shall be shown on the drawing. If
extra dimensions would be useful, but are not necessary, they may be noted as
should be used to attributes and arranged in such a way as to show the purpose
of the features. In addition, dimensions should not be subject to more than one
of manufacturing systems should be avoided. The geometry should be explained
without defining the technique of manufacture.
some sizes are needed during manufacturing but are not wanted in the final
geometry they should be noticeable as non-mandatory.
dimensioning and tolerance should be placed for utmost readability and should
be used to visible lines in true profiles.
geometry is usually restricted by code, the dimension(s) shall be integrated
with code number in comments below the dimension.
not openly declared, all dimensions and tolerances are only suitable when the
item is in free.
Dimensions and tolerances indicate to
the full length, width, and depth.
2. Tolerance Symbols
for tolerances are bilateral unless otherwise defined. For example, the
location of a hole has a tolerance of .020mm. This indicates that the hole can
move +/- .010 mm, which is an equal bilateral tolerance. It does not consider
that the hole can move +.015/-.005 mm, which is an unequal bilateral tolerance.
Symbols for Geometric Tolerance