fits and tolerance

1. Working Drawings
S. P.
Gaikwad

2. First, here’s what we talked
about last time…
Applying Tolerances

3. Representing Tolerance Values
∙ Tolerance is the total amount a
dimension may vary and is the
difference between the maximum
and minimum limits.
(A) Tolerance = .04
(B) Tolerance = .006
∙ Tolerances are represented
as Direct Limits (A) or as
Tolerance Values (B).

4. Important Terms of Toleranced Parts
A System is two or more mating parts.
Nominal Size is used to describe the general size (usually in fractions).
Basic Size – theoretical size used as a starting point for the application of
tolerances (written in decimals).

5. Important Terms of Toleranced Parts
Actual Size is the measured size of the finished part after machining.
Limits – the maximum and minimum sizes shown by the tolerance dimension.
The large value on each part is the Upper Limit, the small value = Lower Limit.

6. Important Terms of Toleranced Parts
Allowance – the tightest fit
between two mating parts.
(The minimum clearance or maximum interference).

7. Important Terms of Toleranced Parts
Maximum Material Condition (MMC)
The condition of a part when it contains
the greatest amount of material.
Least Material Condition (LMC)
The condition of a part when it contains
he least amount of material possible.

8. Important Terms of Toleranced Parts
Piece tolerance
The difference between the upper and lower limits of a single part
(.002 on the insert in this example, .004 on the slot.).
System tolerance
The sum of all the piece tolerances.
For this example (.006)

9. Fit Types:
A Clearance Fit occurs when two toleranced mating parts will
always leave a space or clearance when assembled.
An Interference Fit occurs when two toleranced mating parts will
always interfere when assembled.

10. Functional Dimensioning
Functional Dimensioning begins with tolerancing the most important features.
Then, the material around the holes is
dimensioned (at a much looser tolerance).
Functional features are those that come in contact with other parts,
especially moving parts. Holes are usually functional features.

11. Occurs when dimensions are taken
Tolerance Stack-up from opposite directions of separate
parts to the same point of an assembly.
Dimensioned Dimensioned
from the from the
left. right.
AVOID THIS!!!

12. Avoiding
Tolerance
Stack-up
Tolerance stack-up can
be eliminated by careful
consideration and
placement of dimensions.
(Dimension from same side).
Better still, relate the two
holes directly to each other,
not to either side of the part.
The result will be the best
tolerance possible of ±0.005.

13. Today’s Lecture - Week 10:
Working Drawings
Generally, a complete set of Working Drawings for
an assembly includes:
1.) Detail Drawings of each non-standard part.
2.) An Assembly or Subassembly drawing showing
all the standard parts in a single drawing.
3.) A Bill of Materials (BOM).
4. A Title Block.

14. A Detail Drawing of a Single
Part Called a Lever

15. Assembly Drawing of a Piston & Rod containing 8 parts.
An assembly drawing normally consists of the following:
1. All parts drawn in their operating position
2. A parts list or Bill of Materials (BOM)
3.Leader lines with balloons indicating all parts.
4. Machining and assembly instructions

16. Detail Drawing of the retainer ring used to
fasten the rod to the piston.

17. Multiview Sectioned Assembly
Drawing of a Spring Pack containing…
Drawing Number
Part Numbers

18. Pictorial Assemblies
Sectioned Assembly

19. Pictorial Assemblies
Technical Illustration (Exploded) Assembly

20. …contain...
Title Blocks
A. Name & Address of Company
B. Title of the Drawing
C. Drawing Number
D. Names and dates of drafters,
checker, issue date ,
contract number, etc.
E. Design Approval
F. Additional Approval Block
G. Drawing Scale
H. Federal Supply Code for
Manufacturers
J. Drawing Sheet Size
K. Actual or estimated weight
L. Sheet Number

21. Parts Lists
The information normally included in a parts list is as follows:
1. Name of the part.
2. A detail number for the part in the assembly.
3. The part material, such as cast iron or bronze.
4. The number of times that part is used in the assembly.
5. The company assigned part number.
6. Other information, such as weight, stock size, etc.

22. Record any changes -
Revision Blocks in upper-right corner
Found

23. General tolerance note for
inch and millimeter
dimensions

24. ANSI drawing sheets with
“zones” located on the
border.

25. Tabular Drawings

26. Fastening Devices
Fastening is a method of connecting or joining
two or more parts together, using devices or
processes.
Mechanical Fastening –Process that uses
manufactured devices (Nuts and Bolts)
Bonding – Using material (Glue, Welding)
Forming – Using component shape itself (HVAC,
Tupperware, Velcro)

27. Threaded Fasteners
First Application of a screw thread was
developed by Archimedes to lift water.
1800’s Joseph Whitworth – English Standard
Screw Threads
1864 – US Screw Thread Standard
1946 – ISO Develops Metric Standard
1948 – US Develops Unified Standard

28. Standard Thread Notations:
Internal Threads
Form Chart
External Threads

29. Specifying Tap Drill Size:
A Tap is a tool used to make threads in holes.
A Die is used to make external threads.

30. Thread Representation:

31. General Types of Fasteners:

32. Finished vs.
Unfinished Bolts:
The difference between a finished and
Unfinished hex head bolt is a washer
Under the head of the finished bolt.

33. Nuts:

34. Cap Screws:
Notice the chamfer (Also found on bolts).

35. Machine Screws:
Machine Screws are finished with flat bottoms instead of chamfered corners.
A ½” Hex Head Machine Screw is used on this week’s assembly drawing.

36. Set Screws:

37. Shoulder Screw:
Check Appendix 33 for the dimensions of the shoulder screw
required for this week’s assembly drawing

38. Retaining Rings:

39. Lock Washers:

40. Pin Types:

41. Standard Key Types:

42. Rivets:

43. Rivets:

44. Springs:

45. Create a complete set
of Working Drawings