Drawing Basics

MACHINE TOOL PRACTICESSECTION A Introduction

Shop Drawing Basics

Machine Tool Practices, 8th Edition

Richard R. Kibbe, John E. Neely, Roland O. Meyer, Warren T. White

2006 Pearson Education, Upper Saddle River, NJ, 07458. All rights reserved

Kibbe, et al., Machine Tool Practices, 8th ed. (C) 2006 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved

Pictorial Sketch Formats The design engineer communicates ideas to the machinist through engineering drawings. Initially, the design process may involve pictorial sketches such as:IsometricObliquePerspective These formats allow an object to be drawn and observed in three dimensions.


Isometric Format The isometric format shows an object as it would appear with its major axes parallel to the three isometric axes of the drawing. The isometric axes are 120 degrees apart.


Oblique Format In the oblique format, one set of a rectangular objects lines are parallel to the plane of the drawing.


Perspective Format Perspective is used by artists and technical illustrators. In perspective, the lines of an object recede to a vanishing point much as they would when viewed by the eye.


Orthographic Format The pictorial drawing formats previously shown are not used in typical machine shop engineering drawings because they distort angles and the actual dimensions of the objects shown. Typical machine shop drawings are almost always in the multiview format called ORTHOGRAPHIC.


The Basic Orthographic ViewSo as not to distort the shape and size of an part, or its features, orthographic drawings always show a face on view of an objects surface or feature. No attempt is made to show an object in three dimensions using only one view.


Orthographic ViewsFRONTTOPRIGHT SDELEFT SIDEBOTTOMREARAUXILIARY

A minimum of two views are always required to show any object in it true size and shape and to provide all necessary dimensions for manufacturing


The Front View The orthographic front view shows the shape of the front surface, overall height, height of the top feature and the left to right dimensions of both lower and upper part features.


The Top View The top view shows the overall shape of the objects top surfaces, left to right and back to front dimensions, but does not reveal the total height of the object or the height of the top portion.


The Right Side View The right side view shows the outline of the right side, the overall height, height of the top and bottom feature and the front to back dimension.


The Left Side View The left side view shows the outline of the left side, the overall height, height of the top and bottom feature and the front to back dimension.


The Rear View The rear view of this object is the same as the front view. Overall heights are seen in this view as well as the left to right dimension.


The Bottom View The bottom view is the same as the top view except that the top portion appears as a dashed or hidden line because it is not visible when observing from the bottom.


All Orthographic Views Any or all of the standard orthographic views may be seen on typical shop drawings. The top, front and right side views are the most common. Each view is positioned on the drawing such that it projects directly into every other view. Through this, the true shape and size of an object is shown and may be dimensioned accordingly.


Cylindrical Objects Cylindrical objects may often be fully drawn using only two standard orthographic views. The front and side or end views may be all that is required to show the object fully and all necessary dimensions may be placed in these two views.


Line TypesSeveral different line types are used on shop drawings. These include:Object lines Center lines Dimension linesHidden lines

Object lines are heavy solid lines. Center lines are light long and short dashed lines and dimension lines are light solid lines. Hidden lines are short dashed lines.


Hidden Lines Object edges and other features that are not directly visible in any orthographic views are shown as dashed lines. These are called hidden lines.


Section Views Section views are used where complex internal details are better seen by cutting away parts of an object. A full section is when an object is fully cut through (AA). A half section is where a partial cut is made (BB). On a drawing, the section cutting plane is identified as well as the direction of view.


Auxiliary Views In some special situations, the standard orthographic views do not reveal the true shape and size of an object. In this example, the dimensions of the sloping surface on the right side of the object is distorted in the right side and top view. This due to the angle of the surface. An auxiliary view may be used to show the true size of this surface. The auxiliary view is projected at right angles to its reference surface.


Dimensioning Styles Dimensions may be either in bar fraction form or in decimal fraction form in the inch system of measurement. Metric dimension are always in decimal form.


Dimensional Tolerances A tolerance is an acceptable range of part size. Tolerances may noted as bilateral, meaning that the range is both above and below the nominal part dimension. A unilateral tolerance range is noted as all above or all below the nominal dimension. Tolerance expressed as high and low limits shows the maximum and minimum acceptable dimension.


Standard Tolerances Where no other specific tolerance is defined on a drawing, standard tolerances may be applied. These are usually specified in the title block of the drawing. Standard tolerance ranges may vary between different manufacturers.


Geometric Dimensions Equally important as size dimensions are dimensions that define form and location of part features. These are called geometric dimensions. Exampes of form geometric dimensions include squarness, flatness pendicularity and roundness. Examples of location geometric dimensions include true feature position.


Thread Symbols and NomenclatureThread nomenclature on shop drawings includes:Major diameter Pitch diameterNumber of threads per inch (TPI) Form of thread (Unified) Series of the thread national coarse (NC) or national fine (NF), Internal or external thread A, or B Class of fit, 1, 2 or 3.


Thread Drawing Notations Thread notations on drawings include major diameter, number of threads per inch (TPI), form (Unified) and series (NC or NF), class of fit (1,2 or 3) and external (A) or internal (B).


Other Drawing Symbols and AbbreviationsOther drawing symbols and abbreviations identify part geometry and machining operations such as:Counter sinking, CounterboringSpot facing,Corner radii, Chamfers, Finish marks Bolt or pitch circle diameters


Production Drawing Formats After original drawings are made they are copied for distribution to the manufaturing shop or displayed on computer terminals at manufacturing stations. If changes in design are made, drawings are revised and new versions are sent to the production shop.


Key TermsFront view Finish marks Hidden lines Geometric dimensions and tolerances Left side view Limits

Auxiliary view Bilateral tolerance Bar fraction dimensions Center lines Dimension lines Bottom view Decimal fraction dimensions


More Key Terms

Right side viewSection viewsStandard tolerancesThread nomenclatureTolerancesTop viewUnilateral tolerance

Line typesMicroinch NotesObject linesOrthographic viewsPictorial formatsRear view


Things to Remember When Reading Shop Drawings.Always be sure to read any and all notes on the drawing. Be sure that the drawing is the latest revision before starting work on a project.


Shop Drawing BasicsText ReferencesFrom Section A- Introduction, read and study: Unit 3 - Reading Drawings


Drawing Basics

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