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

THREADS, THREADS, FASTENERS,FASTENERS,

AND SPRINGSAND SPRINGSC H A P T E R T W E LV E

Technical Drawing with Engineering Graphics, 14/eGiesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman

© 2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. • All Rights Reserved.

OBJECTIVESOBJECTIVES

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.



UNDERSTANDING THREADS AND UNDERSTANDING THREADS AND FASTENERSFASTENERS

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/GettyImages, Inc.-Photodisc.)



SCREW THREAD TERMSSCREW THREAD TERMS

Screw Thread Nomenclature

Study Page 455 of your textbook for all thread and fastener terms



SCREW THREAD FORMSSCREW THREAD FORMS



THREAD PITCHTHREAD PITCH

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



THREAD SERIESTHREAD SERIESThe 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



RIGHT-HAND AND LEFT-HAND RIGHT-HAND AND LEFT-HAND THREADSTHREADS

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.



SINGLE AND MULTIPLE THREADSSINGLE AND MULTIPLE THREADSA 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.



AMERICAN NATIONAL THREAD AMERICAN NATIONAL THREAD FITSFITS

AND AND METRIC AND UNIFIED THREAD METRIC AND UNIFIED THREAD

FITSFITSFor general use, three classes of fits between mating threads (as between bolt and nut) have been established by ANSI. These fits are produced by the application of tolerances listed in the standard and are as follows:

• Class 1 fit

• Class 2 fit

• Class 3 fitThere are two general classes of metric thread fits:

• 6H for internal threads

• 6g for external threads



THREE METHODS FOR DRAWING THREE METHODS FOR DRAWING THREADTHREAD

1. Detailed

2. Schematic

3. Simplified



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



EXTERNAL THREAD SYMBOLSEXTERNAL THREAD SYMBOLS

Schematic threads are indicated by alternating long and short lines.

With Simplified representations, threaded portions are indicated byhidden lines parallel to the axis at the approximate depth of the thread, whether the cylinder appears rectangular or circular.



INTERNAL THREAD SYMBOLSINTERNAL THREAD SYMBOLSThe only differences between the schematic and simplified internal thread symbols occur in the sectional views.

In the case of blind tapped holes, the drill depth normally is drawn at least three schematic pitches beyond the thread length



DETAILED REPRESENTATION: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 left-hand threads the linesslope upward to the left

Notice that for right-hand threads the linesslope upward to the right



DETAILED REPRESENTATIONDETAILED REPRESENTATION (EXTERNAL AND INTERNAL (EXTERNAL AND INTERNAL

SQUARE THREAD):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.



THREADS IN PHANTOM AND THREADS IN PHANTOM AND ASSEMBLIESASSEMBLIES

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.



AMERICAN NATIONAL AMERICAN NATIONAL STANDARD PIPE THREADSSTANDARD PIPE THREADS

American National Standard Taper Pipe Thread. (Reprinted from ASME B1.20.1-1983 (R1992), by permission of The American Society of Mechanical Engineers. All rights reserved.)

The tapered profile of the pipe thread…



BOLTS, STUDS, AND SCREWSBOLTS, STUDS, AND SCREWSThe 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.



SCREW HEADSSCREW HEADS

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.

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.



TAPPED HOLESTAPPED HOLESWhen 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.



DRAWING STANDARD BOLTSDRAWING STANDARD BOLTSBolt Proportions (Regular)



LOCKNUTS AND LOCKING LOCKNUTS AND LOCKING DEVICESDEVICES

Many types of special nuts and devices to prevent nuts from unscrewing are available, and some of the most common areShown below.



STANDARD CAP SCREWSSTANDARD CAP SCREWSCap screws are normally finished and are used on machine tools and other machines when accuracy and appearance are important.



STANDARD MACHINE SCREWSSTANDARD MACHINE SCREWSMachine screws are similar to cap screws but are usually smaller (.060" to .750" diameter) and the threads generally go all the way to the head.

Clearance holes and counterbores shouldbe made slightly larger than the screws.Typical machine screw notes are…



Set Screws. (Courtesy of Penninsula Components Inc.)

STANDARD SET SCREWSSTANDARD SET SCREWSA set screw is screwed into one part so that its point bears firmly against another part. Ifthe point of the set screw is cupped, or if a flat is milled on the shaft, the screw will hold much more firmly.

Set screws are specified as follows…



AMERICAN NATIONAL AMERICAN NATIONAL STANDARD WOOD SCREWSSTANDARD WOOD SCREWS

(Courtesy of Michael Newman/

PhotoEdit Inc.)

Wood screws with three types of heads—flat, round, and oval—have been standardized.



MISCELLANEOUS BOLTS AND MISCELLANEOUS BOLTS AND SCREWSSCREWS



KEYSKEYSKeys are used to prevent movement between shafts and wheels, couplings, cranks, and similar machine parts attached to or supported by shafts.

Typical specifications for keys are…



MACHINE PINS AND RIVETSMACHINE PINS AND RIVETS

Taper Pin

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.

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.



RIVET SYMBOLSRIVET SYMBOLSBecause 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. Therivets driven in the shop are called shop rivets, and those driven on the job are called field rivets.



SPRINGSSPRINGSA 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 magneticforces.

Springs. Norton, Robert L., Machine Design: An Integrated Approach, 3rd, © 2006. Printed and electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.)

Steps in Detailed Representation of Spring

C H A P T E R T H I R T E E N

WORKING WORKING DRAWINGSDRAWINGS



OBJECTIVESOBJECTIVES

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.



TOP-DOWN VERSUS BOTTOM-UP TOP-DOWN VERSUS BOTTOM-UP DESIGNDESIGN

Top down refers to starting the process of designing aproduct or system by considering the function of the entiresystem, then breaking that down into subassemblies or component groups based on their major functionsBottom 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.)



CONSTRAINING 3D ASSEMBLY CONSTRAINING 3D ASSEMBLY MODELSMODELS

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.



ASSEMBLY DRAWINGSASSEMBLY DRAWINGSAn 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 ofDynojet Research, Inc.)



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



IDENTIFICATIONIDENTIFICATIONCircled 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.)



MULTIDETAIL DRAWINGSMULTIDETAIL DRAWINGSWhen 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



PARTS LISTSPARTS LISTSA 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.)



ASSEMBLY SECTIONSASSEMBLY SECTIONSIn assembly sections it is necessary not only to show the cut surfaces but also todistinguish between adjacent parts. Do this by drawing the section lines in opposing directions.

Symbolic Section Lining



OTHER ASSEMBLIESOTHER ASSEMBLIES

A working drawing assembly, is a combined detail and assemblydrawing.An assembly made specifically to show how to install or erect a machine or structure is an installation assembly

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.



DIGITAL DRAWING DIGITAL DRAWING TRANSMITTALTRANSMITTAL

Using electronic files saves trees, makes it quicker to distribute and store documents, and allows others to review documents from various applications.

A Portion of a PDF File Showing RedlinedMarkups. (Courtesy of Dynojet Research, Inc.)

Electronic file formats such as Portable Document Format(PDF), originally developed by Adobe Systems in 1993, allowthe originator to send a document that can be commented onwithout allowing the original document to be changed.



TITLE AND RECORD STRIPSTITLE AND RECORD STRIPS

The following should generally be given in the title form:

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.

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.)



CHECKING DRAWINGSCHECKING DRAWINGSThe 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.



DRAWING REVISIONSDRAWING REVISIONSThe 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,”



SIMPLIFYING DRAWINGSSIMPLIFYING DRAWINGS

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.

It makes sense to reduce drawing costs by using practices to simplify your drawings without losing clarity.



PATENT DRAWINGSPATENT DRAWINGS

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.)

Drawings for patent applications are pictorial and explanatory in nature; thereforethey are not as detailed as working drawings for production purposes. Centerlines,hidden lines, dimension notes, and so forth, are omitted, since specificdimensions, tolerances, and notes are often not required to patent the general designor innovation.

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