BLUEPRINT READING AND SKETCHING

Published by
NAVAL EDUCATION AND TRAINING PROFESSIONAL DEVELOPMENT  AND TECHNOLOGY CENTER, 1994
    

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PREFACE

By enrolling in this self-study course, you have demonstrated a desire to improve yourself and the Navy. Remember, however, this self-study course is only one part of the total Navy training program. Practical experience, schools, selected reading, and your desire to succeed are also necessary to successfully round out a fully meaningful training program.

COURSE OVERVIEW: Upon completing this nonresident training course, you should understand the basics of blueprint reading including projections and views, technical sketching, and the use of blueprints in the construction of machines, piping, electrical and electronic systems, architecture, structural steel, and sheet metal.

THE COURSE: This self-study course is organized into subject matter areas, each containing learning objectives to help you determine what you should learn along with text and illustrations to help you understand the information. The subject matter reflects day-to-day requirements and experiences of personnel in the rating or skill area. It also reflects guidance provided by Enlisted Community Managers (ECMs) and other senior personnel, technical references, instructions, etc., and either the occupational or naval standards, which are listed in the Manual of Navy Enlisted Manpower Personnel Classifications and Occupational Standards, NAVPERS 18068.

THE QUESTIONS: The questions that appear in this course are designed to help you understand the material in the text.

VALUE: In completing this course, you will improve your military and professional knowledge. Importantly, it can also help you study for the Navy-wide advancement in rate examination. If you are studying and discover a reference in the text to another publication for further information, look it up.

1994 Edition Prepared by
MMC(SW) D. S. Gunderson


MACHINE DRAWING

When you have read and understood this chapter, you should be able to answer the following learning objectives:
- Describe basic machine drawings.
- Describe the types of machine threads.
- Describe gear and helical spring nomenclature.
- Explain the use of finish marks on drawings.

This chapter discusses the common terms, tools, and conventions used in the production of machine
drawings.

COMMON TERMS AND SYMBOLS
In learning to read machine drawings, you must first become familiar with the common terms, symbols, and conventions defined and discussed in the following paragraphs.

GENERAL TERMS
The following paragraphs cover the common terms most used in all aspects of machine drawings.
Tolerances Engineers realize that absolute accuracy is impossible, so they figure how much variation is permissible. This allowance is known as tolerance. It is stated on a drawing as (plus or minus) a certain amount, either by a fraction or decimal. Limits are the maximum and/or minimum values prescribed for a specific dimension, while tolerance represents the total amount by which a specific dimension may vary. Tolerances may be shown on drawings by several different methods; figure 4-1 shows three examples. The unilateral method (view A) is used when variation from the design size is permissible in one direction only. In the bilateral method (view B), the dimension figure shows the plus or minus variation that is acceptable. In the limit dimensioning method (view C), the maximum
and minimum measurements are both stated The surfaces being toleranced have geometrical characteristics such as roundness, or perpendicularity to another surface. Figure 4-2 shows typical geometrical characteristic symbols. A datum is a surface, line, or point from which a geometric position is to be determined or from which a distance is to be measured. Any letter of the alphabet except I, O, and Q may be used as a datum identifying symbol. A feature control symbol is made of geometric symbols and tolerances. Figure 4-3 shows how a feature control symbol may include datum references.

Fillets and Rounds
Fillets are concave metal corner (inside) surfaces. In a cast, a fillet normally increases the strength of a metal corner because a rounded corner cools more evenly than a sharp corner, thereby reducing the possibility of a break. Rounds or radii are edges or outside corners that have been rounded to prevent chipping and to avoid sharp cutting edges. Figure 4-4 shows fillets and rounds.

Slots and Slides
Slots and slides are used to mate two specially shaped pieces of material and securely hold them
together, yet allow them to move or slide. Figure 4-5 shows two types: the tee slot, and the dovetail slot. For examples, a tee slot arrangement is used on a milling machine table, and a dovetail is used on the cross slide assembly of an engine lathe.

Keys, Keyseats, and Keyways A key is a small wedge or rectangular piece of metal inserted in a slot or groove between a shaft and a hub to prevent slippage. Figure 4-6 shows three types of keys. Figure 4-7 shows a keyseat and keyway. View A shows a keyseat, which is a slot or groove on the outside of a part into which the key fits. View B shows a keyway, which is a slot or groove within a cylinder, tube, or pipe. A key fitted into a keyseat will slide into the keyway and prevent movement of the parts.

SCREW THREADS
Draftsmen use different methods to show thread on drawings. Figures 4-8 through 4-11 show several of them. Now look at figure 4-12. The left side shows a thread profile in section and the right side shows a common method of drawing threads. To save time, the draftsman uses symbols that are not drawn to scale. The drawing shows the dimensions of the threaded part but other information may be placed in “notes” almost any place on the drawing but most often in the upper left corner. However, in our example the note is directly above the drawing and shows the thread designator “1/4-20 UNC-2.” The first number of the note, 1/4, is the nominal size which is the outside diameter. The number after the first dash, 20, means there are 20 threads per inch The letters UNC identify the thread series as Unified National Coarse. The last number, 2, identifies the class of thread and tolerance, commonly called the fit. If it is a left-hand thread, a dash and the letters LH will follow
the class of thread. Threads without the LH are right-hand threads. Specifications necessary for the manufacture of screws include thread diameter, number of threads per inch, thread series, and class of thread The two most widely used screw-thread series are (1) Unified or National Form Threads, which are called National Coarse, or NC, and (2) National Fine, or NF threads. The NF threads have more threads per inch of screw length than the NC.

Classes of threads are distinguished from each other by the amount of tolerance and/or allowance specified. Classes of thread were formerly known as class of fit, a term that will probably remain in use for many years. The new term, class of thread, was established by the National Bureau of Standards in the Screw-Thread


CONTENTS

CHAPTER PAGE
1. Blueprint Reading
2. Technical Sketching
3. Projections and Views
4. Machine Drawings
5. Piping Systems
6. Electrical and Electronics Prints
7. Architectural and Structural Steel Drawings
8. Developments and Intersections

APPENDIX
I. Glossary
II. Graphic Symbols for Aircraft Hydraulic and
Pneumatic Systems
III. Graphic Symbols for Electrical and Electronics Diagrams
IV. Deleted
V. References Used to Develop the TRAMAN


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