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Machine drawing
MACHINE DRAWING
A TEXT AND PROBLEM BOOK FOR TECHNICAL STUDENTS AND DRAFTSMEN
BY CARL L. SVENSEN, M.E.
Professor of Engineering Drawing, Texas Technological College, Member American Society of Mechanical Engineers, Society for Promotion of Engineering Education. Formerly Professor of Engineering Drawing, Ohio State University
NEW YORK, D. VAN NOSTRAND COMPANY, INC., 1921,
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PREFACE
Machine drawing may be considered as:
1. A final stage of a course in mechanical drawing.
2. A course in practical drafting.
3. A transition course between mechanical drawing and machine design.
4. An introductory or first course in machine design.
5. A course for the correlation of drawing and engineering.
The importance of such a course is well recognized but the means of attaining success is not so readily available as for many other courses. This book is planned to make available a guide for the development of an understanding of the relation of machine drawing to engineering. The text is kept as brief as a clear presentation of the subject matter permits. It is designed for advanced courses for students who have had previous instruction in mechanical drawing. A brief chapter on elementary principles is given as an introduction to the course and for review purposes or reference.
A complete treatment of the subject of working drawings, drafting-room practice and idiomatic expressions of the engineering language is followed by a chapter on the principles and practice of dimensioning. The classification of size specification by means of two kinds of dimensions, six cases of the elements of dimensioning, and four systems of dimensioning will, it is hoped, make this subject a definite study.
A study of the common machine details, empirical machine design, jigs and fixtures, etc., are included as properly belonging to an advanced course in machine drawing.
A textbook obtains much of its value from the number, variety, and character of the problems which it contains. The collection of problems in this book (about two hundred) is arranged under headings in a single chapter where they can be conveniently found. Necessary instructions, hints, and references to the text are given so that the student has a definite task whether assigned a simple machine part or the study of a complete machine. The problems are presented by layouts or other specifications so that the instructor is relieved of the preliminary details which ordinarily arise when assigning machine drawing studies.
The scope of the text and the variety and extent of the illustrations and problems is such that it is believed that the special needs of thorough courses in machine drawing in technical institutions can be efficiently served.
1. A final stage of a course in mechanical drawing.
2. A course in practical drafting.
3. A transition course between mechanical drawing and machine design.
4. An introductory or first course in machine design.
5. A course for the correlation of drawing and engineering.
The importance of such a course is well recognized but the means of attaining success is not so readily available as for many other courses. This book is planned to make available a guide for the development of an understanding of the relation of machine drawing to engineering. The text is kept as brief as a clear presentation of the subject matter permits. It is designed for advanced courses for students who have had previous instruction in mechanical drawing. A brief chapter on elementary principles is given as an introduction to the course and for review purposes or reference.
A complete treatment of the subject of working drawings, drafting-room practice and idiomatic expressions of the engineering language is followed by a chapter on the principles and practice of dimensioning. The classification of size specification by means of two kinds of dimensions, six cases of the elements of dimensioning, and four systems of dimensioning will, it is hoped, make this subject a definite study.
A study of the common machine details, empirical machine design, jigs and fixtures, etc., are included as properly belonging to an advanced course in machine drawing.
A textbook obtains much of its value from the number, variety, and character of the problems which it contains. The collection of problems in this book (about two hundred) is arranged under headings in a single chapter where they can be conveniently found. Necessary instructions, hints, and references to the text are given so that the student has a definite task whether assigned a simple machine part or the study of a complete machine. The problems are presented by layouts or other specifications so that the instructor is relieved of the preliminary details which ordinarily arise when assigning machine drawing studies.
The scope of the text and the variety and extent of the illustrations and problems is such that it is believed that the special needs of thorough courses in machine drawing in technical institutions can be efficiently served.
CHAPTER III - MACHINE DRAWING
70. Working Drawings. Any drawing used to give information and directions for doing work is a working drawing.
Such drawings are made by architects and civil, mechanical, and electrical engineers, for buildings, bridges, power plants, machine shops and all kinds of industrial work. This book treats of present practice in machine drawing.
71. There are two general classes of machine drawings assembly drawings and detail drawings. These have been listed as follows:
A. Assembly drawings in outline or section. Design lay-out drawings. Erection drawings. Skeleton or diagram drawings.
B. Assembly working drawings. Part assembly working drawings. Location drawings to show relation of parts with dependent dimensions and fits for two or more details. Tool, jig and fixture drawings.
C. Detail working drawings. General purpose drawings. Pattern drawings. Machine drawings. Forging drawings, etc.
73. Detail Drawings. A detail drawing, Fig. 74, is one which contains the necessary views of each single piece, completely dimensioned and with specifications as to material, machining, etc.
1. Choose views which will completely describe the shape of the piece.
2. Do not draw unnecessary views.
3. Views should carry dimensions without crowding.
4. Choose a scale that will show the piece clearly.
5. Choose a scale that will not require crowding of dimensions.
6. Detail drawings are made full size, half size, quarter size or eighth size.
7. Avoid the use of different scales on same sheet when possible.
8. Arrange detail parts in the same position and order that they will have in the assembled machine when this is possible.
9. Keep views of each part near together but do not crowd them.
10. Leave a space between views of different pieces.
11. When possible, details that are closely related mechanically should be kept on the same sheet.
12. Make detail drawings so complete that no additional information will be required for duplicating the parts shown.
13. Small parts may be grouped together as: small castings; bronze and composition castings; forgings; bolts and screws, etc.
14. Standard small parts such as pressure gauges, oil and grease cups, lubricators, valves, ball bearings, etc., which can be described by notes can be drawn in outline or not at all.
15. If special or extra views of any kind are used, they must be defined by explanatory notes.
74. Making a Detail Drawing. There are three major considerations when starting a detail drawing.
(a) Choice of Views,
(6) Treatment of Views,
(c) Choice of Scale.
A freehand layout sketch is very convenient and helpful, especially when standard size drawing sheets must be used.
78. Blue Printing. Blue prints are made on sensitized paper as follows:
Place a tracing with the inked side next to the glass of a printing frame, Fig. 77. Next place a piece of blue print paper on the tracing, coated side down. Follow this with a felt pad and close the frame. Expose to direct sunlight as indicated at II. The length of exposure varies from 30 seconds in strong sunlight with rapid printing paper to three or four minutes under the same conditions with slow printing paper. After exposing, the paper is removed and washed in clear water. New paper has a yellow color on the coated side which changes to a gray-bronze after exposure. Electric light is very generally used in large plants and for commercial blue printing. Machines for this purpose as well as many other methods of duplication are described in drawing supply catalogs.
79. Assembly Drawings. As already indicated, assembly drawings may be made for almost any purpose. For showing the general appearance of a machine and giving center and overall dimensions an outline assembly such as Fig. 78 is used.
It is sometimes desirable to give all the dimensions on an assembly drawing so that the machine can be built from it. This gives an assembly working drawing. A part or group assembly drawing shows a group of parts in their relation to each other. If dimensioned, no detail drawings are needed.
Piping or wiring diagrams are assembly drawings made to show the sizes, location and arrangement of pipes and wires. When drawn to scale and completely dimensioned, they are called piping or wiring drawings.
Erection drawings show the order of putting parts together, dimensions for center distances, location of oil holes, valves, switches, etc.
80. Making an Assembly Drawing. The purpose for which the drawing is desired must first be considered, after which the proper selec- tion of views must be made. The next step is to determine the position of the views on the sheet and the scale to be used. The detail drawings are then collected ready for reference.
CONTENTS
PREFACE
CHAPTER I
ELEMENTARY PRINCIPLES
- Machine Drawings
- The Pencil
- The Scale
- Scales used on Machine Drawings
- Inking
- Care of the Pen
- Character of Lines
- Cleaning and Erasing
- Accuracy and Neatness
- Shop Drawings
- Reading Views
- Placing Views
- First and Second Positions of Side Views
- Auxiliary Views
- Sectional Views
- Engineering Handbooks
- A. S. M. E, and Other Standards
- Lettering
- Slant Letters and Numbers
- Lower Case Letters
- Fractions
- Titles.
CHAPTER II
FASTENINGS FOR MACHINERY
- Kinds of Fastenings
- Screw Threads
- The Square Thread
- Pitch and Lead
- Conventional Representation of Screw Threads
- Threaded Holes
- Specifications of Screw Threads
- Pipe Threads
- U. S. Standard Bolts and Nuts
- To Draw a Bolt Head or Nut Across Flats
- To Draw a Bolt Head or Nut Across Corners
- Rounded Type of Bolt
- Bolt Chart
- Bolts and Studs
- Cap Screws
- Machine Screws
- Set Screws
- S. A. E. Bolts
- Miscellaneous Bolts
- Miscellaneous Screws
- Locking Devices
- Flanges and Bolting
- Strength and Number of Bolts
- Stress in Bolts
- Keys
- Riveting
- Rivet Heads
- Rivet Holes
- Calking
- Lap Joints
- Butt Joints
- Miscellaneous Connections
- Rolled Steel Shapes
- Pins and Washers.
CHAPTER III
MACHINE DRAWING
- Working Drawings
- Classes of Machine Drawings
- Main Assembly Drawings
- Detail Drawings
- Particular Considerations
- Making a Detail Drawing
- Tracing
- Order of Inking
- Blue Printing
- Assembly Drawings
- Making an Assembly Drawing
- Identification, Record, Etc.
- Idioms of Drawing
- Treatment of Sectional Views
- "Sliced" Sections
- Half Sections
- Symbols for Sectioning
- Common Uses and Treatments of Sections
- Revolved Sections
- Treatment of Ribs and Special Sections
- "Herringbone" Sectioning
- "Phantom" Views
- Developed Sections Contour and Continuity
- Special Views.
CHAPTER IV
PRINCIPLES AND PRACTICE OF DIMENSIONING
- Dimensioning
- Notation of Dimensioning
- Dimension Line
- Arrowhead
- Witness Line
- Pointing Line
- Machined Surfaces
- The Finish Symbol
- Elements of Dimensioning
- Size Dimensions
- Location Dimensions
- The Six Cases
- Systems of Dimensioning
- Location of Dimensions
- Methods of Finishing
- Dimensioning Arcs and Curves
- Dimensioning Angles and Tapers
- Dimensioning in Crowded Places
- Dimensioning Shafts and Cylindrical Pieces
- Dimensioning Wood Constructions
- Dimensioning for Interchangeable Manufacture
- Limit Dimensions
- Basic Dimensions
- General Rules
- Checking Drawings
CHAPTER V
MACHINE DETAILS
- Machine Operations
- Graphical Data and Dimensions
- Engine Details
- Pistons
- Crossheads
- Connecting Rods
- Eccentrics
- Cranks
- Levers,
- Handles, Etc
- Stuffing Boxes
- Fillets, Rounds, Arcs, Etc
- Flanges
CHAPTER VI
BEARINGS, PULLEYS, ETC
- Bearings
- Bushings
- Bearing Metals
- Babbitt
- Bearing "Boxes"
- Simple Bearings
- Hangers
- Pulleys
- Belt Length
- Horsepower Transmitted by Belts
- Pulley Proportions
- "Crowning"
- Rims
- Pulley Arms
- Split Pulleys.
CHAPTER VII
SHAFTING AND COUPLINGS
- Shafting
- Standard Sizes
- Special Shafts
- To Compute the Diameter of a Shaft
- Twisting Moment
- Hollow Shaft
- Horsepower Transmitted
- Table of Constants
- Shaft for Bending and Twisting
- Shaft Details
- A Shafting Drawing
- Couplings
- Solid Sleeve Couplings
- Clamp Couplings
- Flange Couplings
- Clutch Couplings.
CHAPTER VIII
JIGS, FIXTURES AND DETAILS
- Jigs and Fixtures
- Fixtures
- Jigs
- Jig and Fixture Drawings
- Considerations
- A Jig Drawing
- A Fixture Drawing
- Fixture Design
- Standard Parts for Jigs and Fixtures
- Standard Bushings
- Standard Parts and Details
- Shop Appliances
- T-Slots, Etc.
CHAPTER IX
GEARS AND CAMS
- Pulleys and Gears
- Ratio of Velocities
- Gear Teeth
- Gear Terms
- Spur Gears
- Spur Gear Drawing
- Bevel Gears
- Worm Gearing
- Cams
- To Draw a Plate Cam
- Pitch Line
- Roller
- Modification
- Kinds of Motion
- Offset Follower
- Cam with Flat Follower
- Cylindrical Cam.
CHAPTER X
PIPING DRAWING
- Piping
- Uses and Materials
- Pipe Sizes
- Piping Fittings, Valves, Etc.
- Flanged Fittings
- Valves
- Valve Seats
- Conventional Representation
- Piping Drawings
- Dimensioning
- Piping Sketches
- Developed or Single Plane Drawings.
CHAPTER XI
PROBLEMS AND STUDIES 143
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