1. THREADS, FASTENERS, AND SPRINGS
C H A P T E R T W E LV E

2. OBJECTIVES 1. Define and label the parts of a screw thread.
2. Identify various screw thread forms.
3. Draw detailed, schematic, and simplified threads.
4. Define typical thread specifications.
5. Identify various fasteners and describe their use.
6. Draw various screw head types.
7. Draw springs.

3. UNDERSTANDING THREADS AND FASTENERS
The three basic applications of Screw threads are as follows:
1. To hold parts together…
2. To provide for adjustment between parts…
3. To transmit power…
Thread Used for Attachment.
(Courtesy of Arthur S. Aubry/Getty
Images, Inc.-Photodisc.)

4. Screw Thread Terms Screw Thread Nomenclature
Study Page 455 of your textbook for all thread and fastener terms
Screw Thread Nomenclature

5. Thread Pitch
The pitch of any thread form is the distance parallel to the axis between corresponding
points on adjacent threads.
The pitch or the number of threads per inch can be measured with a scale or
with a thread pitch gage.

6. Thread Series
The thread series is the detail of the shape and number of threads per inch composing different groups of fasteners.
Five series of threads were used in the old ANSI standards:
Coarse thread
Fine thread
8-pitch thread
12-pitch thread
16-pitch thread

7. Right-Hand and Left-Hand Threads
Aright-hand thread is one that advances into a nut when turned clockwise, and a left-hand thread is one that advances into a nut when turned counterclockwise.

8. Single and Multiple Threads
A single thread, as the name implies, is composed of one ridge, and the lead is therefore equal to the pitch.
Multiple threads are used wherever quick motion, but not great power, is desired, as on ballpoint pens, toothpaste caps, valve stems, and so on.

9. Three Methods for Drawing Thread
Detailed
Schematic
Simplified

10. THREAD NOTES
ASME/ANSI Y14.6, Screw Thread Representation, is a standard for representing, specifying, and dimensioning screw threads on drawings

11. EXTERNAL THREAD SYMBOLS
With Simplified representations, threaded portions are indicated by
hidden lines parallel to the axis at the approximate depth of the thread, whether the cylinder appears rectangular or circular.
Schematic threads are indicated by alternating long and short lines.

12. DETAILED REPRESENTATION:
METRIC, UNIFIED, AND AMERICAN NATIONAL THREADS
The detailed representation for metric, unified, and American national threads is the same, since the flats are disregarded.
Notice that for right-hand threads the lines
slope upward to the right
Notice that for left-hand threads the lines
slope upward to the left

13. DETAILED REPRESENTATION (External and Internal Square Thread):
Sometimes in assemblies the root and crest lines may be omitted from the nut only portion of the drawing so that it is easier to identify the inserted screw.

14. Threads in PHANTOM and Assemblies
Use phantom lines to save time when representing identical Features Threaded shafts and springs may be shortened without using conventional breaks but must be correctly dimensioned.
When external and internal threads are sectioned in assembly, the V’s are required to show the threaded connection.

15. BOLTS, STUDS, AND SCREWS
The term bolt is generally used to denote a “through bolt” that has a head on one end, is passed through clearance holes in two or more aligned parts, and is threaded on the other end to receive a nut to tighten and hold the parts together.

16. Screw Heads
A machine screw is similar to a slotted head cap screw but usually smaller. A set screw is a screw, with or without a head, that is screwed through one member and whose special point is forced against another member to prevent motion between the two parts.
Do not section bolts, nuts, screws, and similar parts when drawn in assembly because they do not have interior detail that needs to be shown.

17. TAPPED HOLES
When an ordinary drill is used to make holes that will be tapped, it is referred to as a tap drill. When drawing the drill point, use an angle of 30° to approximate the actual 31° slope of the drill bit. The thread length is the length of full or perfect threads. The tap drill depth does not include the cone point of the drill.

18. DRAWING STANDARD BOLTS
Bolt Proportions (Regular)

19. Locknuts and Locking Devices
Many types of special nuts and devices to prevent nuts from unscrewing are available, and some of the most common are
Shown below.

20. STANDARD CAP SCREWS
Cap screws are normally finished and are used on machine tools and other machines when accuracy and appearance are important.

21. MACHINE PINS and RIVETS
Machine pins include taper pins, straight pins, dowel pins, clevis pins, and cotter pins. For light work, taper pins can be used to fasten hubs or collars to shafts.
Taper Pin
Note that the rectangular view of each rivet shows the shank of the rivet with both heads made with circular arcs, and the circular view of each rivet is represented by only the outside circle of the head.

22. Rivet Symbols
Because many engineering structures are too large to be built in the shop, they are built in the largest units possible and then are transported to the desired location. Trusses are common examples. The
rivets driven in the shop are called shop rivets, and those driven on the job are called field rivets.

23. SPRINGS
A spring is a mechanical device designed to store energy when deflected and to return the equivalent amount o f energy when released, ANSI Y14.13M. Springs are commonly made of spring steel, which may be musicwire, hard-drawn wire, or oil-tempered wire. Other materials used for compression springs include stainless steel, beryllium copper, and phosphor bronze. Urethane plastic is used in applications where conventional springs would be affected by corrosion, vibration, or acoustic or magnetic
forces.
Steps in Detailed Representation of Spring
Springs. Norton, Robert L., Machine Design: An Integrated Approach, 3rd, © Printed and electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.)

24. WORKING DRAWINGS
C H A P T E R T H I R T E E N

25. OBJECTIVES 1. Define top-down, bottom-up, and middle-out design.
2. Discuss methods of constraining assemblies made using solid
modeling and parametric modeling.
3. Identify the elements of a detail drawing.
4. List the parts of an assembly drawing.
5. List six types of assembly drawings.
6. List the role of the record strip and title block in the approval
process.
7. Describe the process for revising drawings.
8. Describe the special requirements of a patent drawing.

26. Top-Down versus Bottom-Up Design
Top down refers to starting the process of designing a
product or system by considering the function of the entire
system, then breaking that down into subassemblies or component groups based on their major functions
Bottom up refers to a design process starting at the part level. Individual components are sized and designed, then the final assembly is built around the design of the parts
Middle out refers to a combination of top-down and bottom-up design methods, where some parts are standardized and others are designed within the context of fitting into the design of the assembly.
(Courtesy of Lunar.)

27. Constraining 3D Assembly Models
With constraint-based modeling software, you use assembly constraints to create relationships between modeled parts. The first part added to the assembly becomes the parent part. Other parts are mated to this parent part to build up the assembly.
Mating parts have features that should fit together. Assembly constraints available in the 3D modeling software let you align mating parts.

28. Assembly Drawings
An assembly drawing shows the assembled machine or structure, with all detail parts in their functional positions or as an exploded view where you can relate the parts to their functional positions.
There are different types of assembly drawings:
1. Design assemblies, or layouts.
2. General assemblies.
3. Detail assemblies.
4. Working drawing assemblies.
5. Outline or installation assemblies.
6. Inseparable assemblies (as in weldments, and others).
3D CAD Model for an Air Brake. (Courtesy of
Dynojet Research, Inc.)

29. SUBASSEMBLIES
A set of working drawings includes detail drawings of individual parts and the assembly drawing showing the assembled unit.

30. IDENTIFICATION
Circled numbers called balloon numbers or ball tags are used to identify the parts in the assembly. Circles containing the part numbers are placed adjacent to the parts, with leaders terminated by arrowheads touching the parts.
(Courtesy of Big Sky Laser.)

31. Multi-detail Drawings
When multiple detail drawings are shown on one sheet, label each part with identification similar to that used on way detail drawings
Portion of a Drawing Showing Identification of Details with a Parts List

32. PARTS LISTS
A parts list or bill of materials itemizes the parts of a structure shown on an assembly drawing.
CAD software often allows you to generate the parts list automatically or somewhat automatically.
(Courtesy of Solidworks Corporation.)

33. ASSEMBLY SECTIONS
In assembly sections it is necessary not only to show the cut surfaces but also to
distinguish between adjacent parts. Do this by drawing the section lines in opposing directions.
Symbolic Section Lining

34. Other Assemblies
After all detail drawings of a unit have been made, it may be necessary to make a check assembly, especially if a number of changes were made in the details.
A working drawing assembly, is a combined detail and assembly
drawing.
An assembly made specifically to show how to install or erect a machine or structure is an installation assembly

35. Digital Drawing Transmittal
Using electronic files saves trees, makes it quicker to distribute and store documents, and allows others to review documents from various applications.
Electronic file formats such as Portable Document Format
(PDF), originally developed by Adobe Systems in 1993, allow
the originator to send a document that can be commented on
without allowing the original document to be changed.
A Portion of a PDF File Showing Redlined
Markups. (Courtesy of Dynojet Research, Inc.)

36. Title and Record Strips
The function of the title and record strip is to show, in an organized way, all necessary information not given directly on the drawing with its dimensions and notes.
The following should generally be given in the title form:
1. Name of the object shown.
2. Name and address of manufacturer.
3. Name and address of the purchasing company, if any.
4. Signature of the person who made the drawing and date of completion.
5. Signature of the checker and date of completion.
6. Signature of the chief drafter, chief engineer, or other official, and the date of approval.
7. Scale of the drawing.
8. Number of the drawing.
(Courtesy of Big Sky Laser, Inc.)

37. CHECKING DRAWINGS
The final checker should systematically review the drawing for any remaining errors. They should study the drawing with particular attention to:
1. Soundness of design, with reference to function, strength, materials, economy, manufacturability, serviceability, ease of assembly and repair, lubrication, and so on.
2. Choice of views, partial views, auxiliary views, sections, lettering, and so on.
3. Dimensions, with special reference to repetition, ambiguity, legibility, omissions, errors, and finish marks. Special attention should be given to tolerances.
4. Standard parts. In the interest of economy, as many parts as possible should be standard.
5. Notes, with special reference to clear wording and legibility.
6. Clearances. Moving parts should be checked in all possible positions to ensure freedom of movement.
7. Title form information.

38. DRAWING REVISIONS “OBSOLETE” “SUPERSEDED BY” or “REPLACED BY”
The record of revisions should show the change, by whom, when, and why the change was made. An engineering change order (ECO) or engineering change request (ECR) is processed to approve and track changes to drawings once they have been released for production.
Any changes or additions made to a drawing are tracked by a revision number. A symbol can be added to the drawing showing the item affected by the revision.
“OBSOLETE”
“SUPERSEDED BY” or “REPLACED BY”
“SUPERSEDES” or “REPLACES,”

39. SIMPLIFYING DRAWINGS
It makes sense to reduce drawing costs by using practices to simplify your drawings without losing clarity.
To simplify drawings:
1. Use word descriptions when practical.
2. Do not show unnecessary views.
3. Use standard symbols such as Ø and standard abbreviations (see Appendix 2 when appropriate).
4. Avoid elaborate, pictorial, or repetitive details. Use phantom
lines to avoid drawing repeated features.
5. List rather than draw standard parts such as bolts, nuts,
keys, and pins.
6. Omit unnecessary hidden lines.
7. Use outline section lining in large areas to save time and
improve legibility.
8. Omit unnecessary duplication of notes and lettering.
9. Use symbolic representation for piping and thread.
10. Use CAD libraries and standard parts when feasible for design
and drawings.

40. PATENT DRAWINGS
Drawings for patent applications are pictorial and explanatory in nature; therefore
they are not as detailed as working drawings for production purposes. Centerlines,
hidden lines, dimension notes, and so forth, are omitted, since specific
dimensions, tolerances, and notes are often not required to patent the general design
or innovation.
Patent Drawing Examples Although several examples are shown here, each drawing is shown on a separate sheet in the patent application. (Courtesy of US. Patent and Trademark Office.)