EGR 277

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Lecture 6 EGR 110 Engineering Graphics
Reading Assignment Ch. L in Engineering
Graphics Workbook, Series 1.2 or Series
2 Sketching Assignment Sketching Assignment 5
Dimensioning Example - Work problem DIM-6 in
class (Engineering Graphics Workbook, Series 1.2,
by Craig Craig). Grids are 0.25.
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Lecture 6 EGR 110 Engineering Graphics
Tolerance Tolerance - the total amount of
variation permitted for a specific
dimension - the difference between the maximum
and minimum limits Limit Dimensions - the minimum
and maximum dimensions

• Example If a dimension is 0.875 ? 0.003,
  determine the
• Maximum dimension
• Minimum dimension
• Limit dimensions
• Tolerance

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Lecture 6 EGR 110 Engineering Graphics
Why is tolerance important? The use of
interchangeable parts would be limited unless the
accuracy of each part was controlled. No parts
can be made to exact size. Even finely machined
parts will vary by some small amount (for
example one thousandth of an inch). Keep in
mind that increased accuracy (smaller tolerance)
results in increased costs. An engineer must
carefully weigh the cost of each tolerance that
he specifies.
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Lecture 6 EGR 110 Engineering Graphics
Tolerance examples Tolerance can be expressed in
various ways. Some examples are shown below.
Symmetrical tolerance
Non-symmetrical tolerance (deviation)
Limit Dimensions
Tolerance is often expressed using notes as shown
below (add hole dimension).
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Lecture 6 EGR 110 Engineering Graphics
Mating Shafts and Cylinders Tolerance is
particularly important in mating parts, such as a
shaft and a cylinder. In some cases the shaft
may fit loosely into a cylinder (clearance fit)
or in other cases it may fit very tightly
(interference fit). With a clearance fit, the
shaft is slightly small than the cylinder and
with an interference fit, the shaft is slightly
larger than the cylinder. A couple of terms are
important with mating shafts and
cylinders Maximum clearance Maximum cylinder
dimension - Minimum shaft dimension Allowance (
minimum clearance) Minimum cylinder dimension -
Maximum shaft dimension Note that allowance will
be negative for an interference fit.
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Lecture 6 EGR 110 Engineering Graphics

• Example For the mating shaft and cylinder
  below, determine
• Shaft tolerance
• Cylinder tolerance
• Maximum clearance
• Allowance
• Is it a clearance fit or an interference fit?

Shaft
?1.753 ?1.750
?1.749 ?1.747
Cylinder