onlinemetallurgy.com

1. Tolerance & Allowance

2. For more help contact me
Muhammad Umair
Bukhari
Engr.umair.bukhari@gmail.com
http://onlinemetallurgy.com

3. Introduction
 Modern industry has developed on the basis of
interchangeable manufacturing.
 Interchangeable manufacturing means production of
parts to such a degree of accuracy as is necessary to
permit assembly and proper functioning of parts
without further machining or fitting.
 To set the dimension for many product we make
certain gages that measure dimensions. So gages
used for interchangeable manufacturing.

4. Tolerance
• “The total amount by which a
given dimension may vary, or the
difference between the limits.”

5. Design Specifications and Tolerance
 Develop from quest for production quality and
efficiency.
 Early tolerances support design’s basic function.
 Mass production brought interchangeability.

6. Affected Areas
Product Design Quality Control
Manufacturing
Engineering
Tolerance

7. Product design
 Product Design has the responsibility
of designing with consideration for
the maximum possible working
tolerances compatible with the
functional requirements of the design.

8. Manufacturing
 Manufacturing has the responsibility
of bringing the design into a physical
entity with consideration for process
methodologies, capabilities and
economics.

9. Quality control
 Quality control has the responsibility
of measuring and evaluating the final
product to ensure the integrity of the
product tolerance.

10. Variation is Unavoidable
• No two manufactured objects are
identical in every way. Some degree
of variation will exist.
• Engineers apply tolerances to part
dimensions to reduce the amount of
variation that occurs.

11. Tolerances
A tolerance is an
acceptable amount
of dimensional
variation that will
still allow an object
to function
correctly.

12. Tolerances
A tolerance is an
acceptable amount
of dimensional
variation that will
still allow an object
to function
correctly.

13. Tolerances
Three basic
tolerances that occur
most often on
working drawings
are: limit
dimensions,
unilateral, and
bilateral tolerances.

14. Limit Dimensions
Limit dimensions are
two dimensional values
stacked on top of each
other. The dimensions
show the largest and
smallest values allowed.
Anything in between these
values is acceptable.

15. These are limit dimensions,
because the upper and
lower dimensional sizes are
stacked on top of each other.
Limit Dimensions

16. Unilateral Tolerance
A unilateral
tolerance exists when
a target dimension is
given along with a
tolerance that allows
variation to occur in
only one direction.

17. This tolerance is
unilateral, because
the size may only
deviate in one direction.
Unilateral Tolerance

18. Bilateral Tolerance
A bilateral
tolerance exists if
the variation from a
target dimension is
shown occurring in
both the positive and
negative directions.

20. Allowance
 Allowance is a planned deviation between an
actual dimension and
a nominal or theoretical dimension, or between an
intermediate-stage dimension and an intended
final dimension

21. example
 Outer dimensions (such as the length of a bar) may be
cut intentionally oversize, or inner dimensions (such as
the diameter of a hole) may be cut intentionally
undersize, to allow for a predictable dimensional change
following future cutting, grinding, or heat-
treating operations.
 For example:the outer diameter of a pin may be ground
to 0.0005 inches (0.013 mm) oversize because it is
known that subsequent heat-treatment of the pin is going
to cause it to shrink by 0.0005 inches (0.013 mm).
 A hole may be drilled 0.012 inches (0.30 mm) undersize
to allow for the material that will be removed by
subsequent reaming.

22. Tolerance ALLOWANCE
 A tolerance is the limit of
acceptable unintended de
viation from a nominal
or theoretical dimension.
Therefore, a pair of
tolerances, upper and
lower, defines a range
within which an actual
dimension may fall while
still being acceptable.
 an allowance is
a planned deviation from
the nominal or theoretical
dimension
 whereas allowance is one
that we give to the
material to undergo some
process in the future.
Difference