HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
BLUEPRINTS/DRAWINGS
The purpose of this document is to familiarize you with the blueprints and drawings of products produced in an Aerospace Environment. This text is general information and may change from one customer’s prints to another’s. Drawings define engineering requirements and are used to support the actual build process of the part. Detail and assembly drawings are commonly used to aid in the production process. Detail drawings give all the information for fabricating single parts, while assembly drawings show two or more parts joined. They may also contain some detail part definition. Detail Drawings A detail is usually one completely defined part. In a detail drawing of a part, the picture sheet and bill of material together give complete manufacturing data needed to fabricate each part. Like most drawings, a detail drawing will typically reference other engineering information such as process specifications (which control manufacturing processes) and standard part specifications (which define standard parts that are used on a variety of drawings). A detail drawing may contain single or multiple parts, but each part usually remains separate and is not joined together. Detail information includes: Size and shape description Tolerance information Stock size and material requirements Heat treating requirements Machine finish requirements Part numbering and marking instructions Hole locations Protective finish Process specifications and standards Next higher drawing number (where the part will be used) Detail drawings can be very small or very large. The size of the drawing picture sheet is determined by the size and complexity of the part being detailed (see Figure 1). Detail drawings do not show location, position, or fastening methods. However, they may give reference information about where a fastener or part will eventually be installed. Most current detail drawings are drawn with Computer Aided Drafting (CAD) software. Therefore, dimensions are usually contained in part model data sets
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
and not shown on picture sheets. CAD software is needed by the manufacturer to determine the size and shape of parts. If a print is controlled by a CAD dataset it will be noted on the picture sheet (see Figure 15). Many older detail drawings are dimensioned or issued as full-scale PCM’s (see Photo Contact Master).
Figure 1: Detail Drawing Assembly (ASSY) Drawings Assembly drawings show how to attach two or more parts or assemblies together. Assembly drawings can also show detail part information. Assembly information includes: List of required components How parts fit together Part numbering and marking instructions Fastening methods Protective finish requirements Process specifications and standards
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Next higher drawing number (where the assembly will be used)
Assembly drawings are easily recognized by their titles. If the word “assembly” or the abbreviation “ASSY” appears in the title, it is an assembly drawing (see Figure 2). If a part is detailed on an assembly drawing, all information needed to make that part will be given. An assembly drawing can show more than one assembly.
Figure 2: Assembly Drawing Picture Sheet Introduction The picture sheet is what most people have in mind when they think about drawings. The picture sheet shows the size and shape of parts and how the parts fit together. Picture sheet forms are standardized. The three main areas of a picture sheet are (see Figure 3): 1. The title block
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
2. The revision block 3. The picture area
Figure 3: Picture Sheet Title Block Area The title block is always located in the lower right corner of the picture sheet. The title block contains the following information (see Figure 4): 1. Drawing number 2. Title 3. Sheet number- Drawing sheets are numbered consecutively starting at Sheet 1. 4. Scale- Scale defines the size of the picture as compared to the size of the actual part. If more than on scale is used, this are says “NOTED,” and the scale is shown under each view in the picture area. 5. Size- Letter size designator indicates the size of the drawing form. 6. Signature Block- Names of the people responsible for the original release of the drawing. 7. The general tolerance that applies to the dimensions on the sheet. 8. Standard preprinted PCM note on un-dimensioned drawings forms. 9. Revision- The latest Drawing Change Notice (DCN) revision of the drawing sheet, indicated by letter. A dash (-) is used to indicate a new drawing sheet.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 4: Title Block Revision Block The revision block is always located in the upper right corner of the picture sheet. It is used to record incorporated changes. The revision block contains the following information (see Figure 5): 1. On zoned picture sheets the ZONE column shows the location where changes have occurred. 2. The REV column shows the latest DCN (Drawing Change Notice) revision of the drawing sheet, indicated by a letter. A dash (-) is used to indicate a new drawing sheet. 3. The Description column describes the changes that were made to the picture sheet. This column also shows the change number, reason, and production information. If ADCNs were incorporated, their numbers will also be listed. 4. The Date and Approved columns show who is responsible for the change. It also shows when the change was made. A separate form is used if there is too much information to fit in the revision block. In that case, the revision block has a note “See DCN” and a date. The DCN is then filed with the picture sheet.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 5: Revision Block Picture Area The drawing picture area shows the detail, assembly, or installation is the remaining area of the picture sheet. Words, symbols, and lines are used to show different views of parts, assemblies, and installations. Specific tolerances or geometric dimensioning and tolerances if used can also be found in the picture area. Picture Sheet Numbering Drawings may have only one picture sheet or they may have many. Picture sheets are listed in numerical order, such as “picture sheet 1,” “…sheet2,” and
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
“…sheet 3.” The drawing will have as many sheets as it takes to convey the information. When a drawing requires more than one picture sheet, it is referred to as a “multi-sheet” drawing. Multi-sheet drawings are used when a part is too large, a part is very complex, and/or there are many variations. Remember, the picture sheet along with the parts list provides complete drawing information. Picture Sheet Sizes Picture sheet size varies from 8-1/2 x 11 inches to 36 x 138 inches. The most commonly used sizes are listed below. The letter designator found in the title block indicates the drawing size. Size 8-1/2 x 11 11 x 17 22 x 34 36 x 50 30 x 46 36 x 94 and/or 36 x 138 Letter Designator “A” size “B” size “C” size “D” size “F” size “J” size
Picture Sheet Zones The borders on some picture sheets contain letters and numbers that divide the picture area into drawing zones. The numbers are located along the bottom and usually also along the top; the letters are located along the right side and usually also along the left side. The letters and numbers provide a zone location that makes it easier to find desired parts or views (see Figure 1 & 2). Smaller drawing forms may not have zones. Picture Sheet Scale Picture sheets will be drawn to an appropriate scale that is determined by Engineering. The scale of a picture sheet is shown in the title block. Although, full is the preferred scale engineering will often use reduced or enlarged scales to show large or small parts in more detail. Examples of scale are: Scale Type No Scale Full (Preferred) Reduced Enlarged Multiple Scale Entry None 1/1 1/2, 1/4, 1/10, 1/20, 1/40 2/1, 4/1 Noted, 1/1 & Noted, 2/1 & Noted, etc.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Un-dimensioned Picture Sheets An un-dimensioned picture sheet is accurately drawn to full scale on stable material which provides a photographically reproduced template for the tooling and fabrication of parts and assemblies (see Figure 6). Un-dimensioned picture sheets are always drawn on heavy drafting film, which is called a “PCM” (Photo Contact Master). This material is dimensionally stable. To get accurate dimension information, you need a dimensionally stable copy of the original PCM. This copy is called an “REPT” (Reference Engineering Template). Measurements can be taken directly from this film. Photo Contact Master The Photo Contact Master is a full-scale production drawing on heavy drafting film (.0075 inch thick), and has letters “PCM” on the picture sheet form. An REPT is available for all PCM drawings; it’s just a matter of producing a scale copy. The heavy drafting film that PCM drawings are drawn on and REPT’s are printed on is called Mylar. You may even hear REPTs or PCMs referred to as “Mylar drawings” or just “Mylars”. There are (3) keys to identifying a PCM drawing: 1. There letters PCM will be printed near the title block usually underneath it. 2. There will be vertical and horizontal grid lines drawn across the picture area of the drawing. These grid lines will be spaced 10 inches apart. (On some older drawings they may be spaced 5 inches apart). 3. There will be an obvious lack of dimensions on the features of parts on the drawing. There may be some dimensions (on close tolerance hole patterns for example) but most features will not have explicit dimensions. The intent is to scale dimensions off the drawing.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 6: PCM Drawing Parts List A parts list is a listing of all components used in the production of a parent item that does not reflect its structure or intermediate levels. Parts lists provide the following information: Part Identification (number, nomenclature, description). Quantity of the part required per assembly or installation. Information that defines the part (such as raw material call-out). Information on how to fabricate the part (process requirements). Where the part is located on the drawing picture sheet. A parts list was designed to go hand in hand with picture sheets. They augment picture sheets with textual information that would be cumbersome and difficult to maintain on the face of a drawing. They also define the Bill of Materials (BOM) which takes part definition from single detail parts, through perhaps several levels of assembly build-up, and finally to installation.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Parts lists can be located on picture sheets right above the title block (see Figure 7), or they can be a separate sheet that is referenced as a sheet number of the drawings (see Figure 8).
Figure 7: Parts List
Figure8: Parts List
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Line Standards, Part Callouts, and Drawing Symbols Line standards, part callouts, and drawing symbols are shown on drawing picture sheets in this section. These are standardized for industrial use. Engineering groups use these standards to describe information contained on picture sheets. Line standards are used to describe geometric characteristics of parts, assemblies, and installation. Part callouts are used to identify items located on the picture sheet. Symbols are used to prevent needless repetition of information and to make the picture sheet easy to read.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Line Standards
Figure 9: Line Standards
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure10: Line Standards
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Part Callouts On the picture sheet parts are identified by their part number. In Figure 11 a -1 ASSY is shown. The 123N5123-1 part is defined on another drawing (we know this because the drafter used the complete part number). The -3 part is defined on this drawing (we know this because the drafter identifies the part with its dash number only). The term “-1 ASSY” in Figure 11 is a View Label that indicates that the view above is the -1 assembly from this drawing. Part numbers defined on other drawings will be called out by their complete part number. This is so the reader of the drawing knows where to go get more information on the part. All parts, except the view label, are called out with the use of leader lines that point to the edge of the part they are associated with. All part numbers shown on the picture sheet, except for some standard parts, will be called out in the parts list. Find Numbers as Part Callouts A find number is: A method for cross referencing an item from the picture area of a drawing to the parts list. A substitute for a part number as a callout on the picture sheet. Enclosed in a circle.
Figure 11: Part Call Out
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Reference Callouts When items are identified with phantom lines for reference purposes, the drawing number is shown without a dash number and the letters REF are shown after the number (see Figure 12).
Figure 12: Reference Call Outs Standard Parts Standard parts are commonly used items purchased in bulk quantities such as: nuts, bolts, rivets, shims, etc. Standard parts are shown on the picture sheet but not always listed in the parts list. Examples of symbols used for fasteners are shown in Figure 13.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Symbols
Figure 13: Symbols
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 14: Symbols Notes
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Notes are used to give more detailed information on drawing sheets. They are usually listed on the first sheet of all drawing sheets. They are labeled and then referenced throughout the other drawing sheets where applicable. There are three types of notes: flagnotes, general notes, and standard notes. Flagnotes, identified by flagnote symbols, pertain to specific information on the drawing picture sheet and are explained in the parts list. Therefore, it is necessary to cross reference the flagnotes with the picture sheets in order to fully understand the engineer’s intent. General notes pertains to the entire drawing and are is not identified on the picture sheets. General notes stand alone. Standard notes used for listing specifications, documents, and industry standards that pertain to all drawings. All production drawings will have the same standard notes. Permanent Type Fasteners Rivets and other permanent fasteners, like hi-loks, and lockbolts, are called out with fastener symbols. The fastener symbol shows the location of the hole and identifies the type of fastener used at that location (see Figure 15). A symbol includes: A two or three letter code in the upper left quadrant to indicate the type of fastener to be installed. The diameter of the fastener, in 32nds of an inch, in the upper right quadrant. A symbol may also include: Grip length, in 16ths of an inch, in the lower right quadrant. Countersink or dimple instructions, in the lower left quadrant.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 15: Fastener Symbols When fastener symbols are shown on a picture sheet, the drawing includes a fastener symbol code block that cross-references the fastener code with the part number of the fastener. The fastener symbol code block is usually in the upper right-hand corner of the picture sheet, next to the revision block (see Figure 16).
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 16: Fastener Symbol Table on Picture Sheet In Figure 17, all fasteners between “YOF/5” fasteners symbols shown are implied to be “YOF/5” fasteners. This is engineering’s way of saving on drafting time and keeping the drawing from getting too “cluttered”.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 17: Permanent Fastener Symbol on Picture Sheet
Removable Fasteners Symbols Removable fasteners, such as nuts and bolts, are not shown using fastener symbol codes. They are shown using a centerline for hole location and a complete part number callout. The hole diameter will be called out explicitly, as shown below (see Figure 18).
Figure 18: Example of Removable Fastener Callouts
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
PICTURE SHEET VIEWS
Standard Airplane Views and Standard Orthographic Views Standard Airplane Views are used on installation drawings whenever part location and position are required. These views follow orthographic view principles. Standard Orthographic Views are used on detail and assembly drawings. Detail parts or assemblies do not require location and/or position information within the airplane structure.
Figure 19: Orthographic View Detail Views A detail view shows an object or an area of an object in greater detail to clarify that area. The detail view is in the same plane as the principle view. Details are usually drawn in a larger scale (see Figure 20). The view is identified by a leader type indicator. A heavy dashed circle around the area is an acceptable alternate.
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 20: Detail View Detail View Rotation Sometimes detail views are rotated to clarify the drawing. They may be rotated in either of two directions. The amount, in degrees, and the direction of rotation is shown with the view identification. In Figure 20, CCW 90 stands for counterclockwise rotation, 90 degrees. Section Views A section view is like a thin slice cut through a part. Section views show interior construction or hidden features that cannot be shown clearly by an outside view. These are sometimes called cross sections. The cross section may be through the whole object, or show only part of an object. A section view is indicated by a cutting plane line with arrowheads. The arrows show the direct from which the view is taken (see Figure 21).
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 21: Section View Auxiliary Views Auxiliary views show features that cannot be shown clearly in standard views. An auxiliary view is indicated by a viewing plane indicator similar to the section cutting plane except that it is placed outside the object. Auxiliary views show the exterior of an object as if looking from a particular direction. They are used to show true size and shape, true angle, and true length of complex objects (see Figure 22).
HOW TO READ AEROSPACE BLUEPRINTS AND DRAWINGS
Figure 22: Auxiliary View Isometric Drawings An isometric drawing shows three sides of a part in the same view. To do this, the part is shown tilted and rotated. Isometric drawings should not be scaled because tilting shortens some of the lines.
Figure23: Isometric View