Appendix B Technical Drawing Elsevier-Free Books

Appendix B Technical Drawing Elsevier
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e2 APPENDIX B Technical Drawing,l To show how parts are assembled. l To indicate manufacturing preferences, Consider the cylindrical mechanical part in Figure B 2 The outside of the part is round with a. hole through the center There is a step in the diameter on the front side and there is a radial hole on. the side of the part The four views shown are complementary The hidden surface drawings are eas. ier to understand but many details are missing The wire frame and hidden line views contain all of. the details but are more confusing and they are not unique For example the orientation of the small. cylinder in the wire frame drawing is arbitrary and could be horizontal or vertical No drawing type is. ideal but when chosen carefully they will maximize effectiveness. The basic and default drawing type for engineering work is based on orthographic projections. These typically use three views from the top side and front of a part The part in Figure B 2 is shown. in Figure B 3 using standard engineering conventions The part is largely symmetrical so only two. views are drawn the front and the side The drawing has a border and a title block on the lower right. side This title block indicates that the part is called Bushing it is made from aluminum and all of. the dimensions are in mm A couple of notes are placed to the left of the title block indicating that. all sharp corners need to be rounded to less than 1 0 mm when removing sharp edges The center. hole feature is to be reamed a precision operation as indicated by note 2 Dimensions are marked. on the part using arrows and extension lines The units are not marked on each number because the. default set in the title block is millimeters The precision of the piece is set by the significant figures. of each dimension For example a dimension of 25 could range from 24 5 to 25 5 whereas a dimen. sion of 25 0 could range from 24 95 to 25 05 Adding a zero will add precision and cost Center lines. are used to indicate a center of roundness they have two small breaks separated by some distance. The dashed lines at the top of the right view are hidden lines showing the hole in the top of the part. The thick black line from A to A indicates a section view a virtual cut through the part The view. to the left has diagonal hash lines where it has cut through the material In this view the hole through. the center and the top hole are very clear to see This drawing also includes geometric tolerancing. and dimensioning GD T symbols The box in the upper right side of the drawing indicates that the. Wire frame Hidden Line Hidden Surface Hidden Surface. Arbitrary feature interpretation,FIGURE B 2,Multiple views of a sample part. APPENDIX B Technical Drawing e3,25 0 0 6 M,Section A A. 100 05 99 95,Part Bushing,1 Break sharp edges to 1 0 max Date May 5 2014.
Materials Al,2 Drill 98 50 ream to spec Units mm, Note historically the drawings were reproduced using a process that resulted in a blue. color and the term blue print remains in common use. FIGURE B 3,A two view drawing of a symmetrical part. center line of the side hole must be within 0 6 mm of the target location The 175 0 mm in the square. box indicates that the location of the small hole must be measured from the far face. The glass box is the basic concept behind three view orthographic drawings A tetrahedral shape. is converted to a three view drawing in Figure B 4 The part is oriented so that most of the detail can. be seen from the front or top of the box Each view is then drawn as it would be seen through that. face of the box This approach ensures that the details of any feature will appear in at least one or. probably two of the views In addition the views do not use perspective This means that lines farther. away are still the same distance apart In cases where parts are symmetrical two views may be suf. ficient to clearly show each feature The top view is placed at the top of the drawing sheet the front. view is placed at the bottom The side view is normally placed on the right side for North American. drawings while the European standard is to place it to the left. e4 APPENDIX B Technical Drawing,freeze the views,cover the part with through each side of. a glass box the glass box,the part a,tetrahedron,unfold the sides to. get a set of views,European method North American method.
FIGURE B 4, A three view drawing of a tetrahedron using a glass box. The example of the tetrahedron is continued in Figure B 5 The lines with two dashes are called. the fold lines these are the edges of the glass box The 45 line is used to match the side front top. views This construction is important because it coordinates a feature across all three views For. example the vertices edges and faces of the tetrahedron can be traced between the views This can. eliminate some arbitrary interpretation, When choosing the orientation of the parts in the drawings it is important to use the front and top. views to convey the most detail The side views are then used for clarification and verification Some. of the general rules for selecting the front and top views include. l It should be a natural front to the object,l It should be the most important view. l The part appears stable,l The views minimize hidden lines in other views. l The views contain most of the detail,APPENDIX B Technical Drawing e5.
R S F F R S,European Standard North American Standard. FIGURE B 5,Spacing multiple drawing views, B 1 How does a perspective view differ from an isometric drawing. B 2 What does a dashed line on a drawing represent. B 3 Draw a wire frame hidden line and hidden surface view of the letter A. B 4 Why does a round part only need two views,B 5 What does a center line represent. B 6 Why are title blocks used on drawings,B 7 Where would a Canadian draw a side view. B 8 Is an orthographic projection a perspective view. e6 APPENDIX B Technical Drawing,B 1 Oblique and isometric projections.
Two dimensional views alone do not always provide a good sense of three dimensional shapes. Effective techniques for adding three dimensions include oblique and isometric projections Both. drawing styles are shown in Figure B 6 In oblique projections the front view is as normal but depth. is set at an angle In isometric projections the faces are all set at 30 or 60 angles Both of these. drawing styles use true length lines so that dimensions can be measured directly The result is that the. drawings are not visually correct but they allow measured precision A square and a rectangle have. been added on the top and front sides to illustrate face locations and feature distortion In the oblique. projection the circle faces the front and is round In the isometric projection it is at an angle and. appears as an oval In both projections the rectangle is distorted Isometric projections are normally. done at 30 angles with each side drawn to scale For oblique projections the angles and depth ratios. These projections are particularly helpful when doing hand sketches of designs and the visual. nature can help concept development,Oblique Projections. cavalier 45 with full depth size,cabinet 0 90 with half depth size. general 0 90 with between half,and full depth size. y axis z axis depth,Isometric Projection,30 degrees 30 degrees. x axis z axis,FIGURE B 6,Oblique and isometric projections for a unit cube.
B 9 What angles are used for a cabinet view,APPENDIX B Technical Drawing e7. B 10 Draw a freehand sketch of the word fun using a an isometric view and. b an oblique view,B 2 Auxiliary views, Sometimes parts have faces or features that are not clear from one of the three drawing views In. these cases an additional view is drawn at an angle An auxiliary view has been added to Figure B 7. to show the diagonal face parallel to the viewing plane this is called a true surface The value of this. arrangement is illustrated with the circle on the inclined face In the normal top and side views the. circle appears to be an oval but it appears correctly in the auxiliary view This example only shows. the face of interest but sometimes all of the details will be added. True Surface,An auxiliary view,from a non standard. FIGURE B 7,An auxiliary view, B 11 Why would a drawing include an auxiliary view. e8 APPENDIX B Technical Drawing,B 3 Notations and features.
There are a few drafting conventions that help professionals to read prints Basic lines are used to. indicate part edges other lines are reference lines as shown in Figure B 8 Construction lines were. used heavily when drafting was done by hand but they remain as very useful to indicate dimension. references Center lines are used to indicate the center of round features A drawing line is a heavier. line used to represent visible edges in a drawing view Hidden lines are used to show lines hidden. behind solid faces to aid understanding Phantom lines are used for other types of reference lines on. drawings When part dimensions are very long break lines are used to show where a part has been. visually cut Dimension lines have arrows on both ends to show dimensions and leader lines have an. arrow on one end for notes Cutting plane lines are very heavy dashed lines to indicate a cutting plane. through the material of a part,Construction line,Center line. Hidden line,Phantom line,Drawing line,Break line,Dimension line. Cutting plane,FIGURE B 8,Special line types, Part dimensions and tolerances are indicated in a drawing with arrows that show the significant. dimension The example on the left in Figure B 9 ranges in size from 1494 5 mm to 1510 5 mm. The example on the right should have a nominal width of 1500 but can be up to 1500 5 or down to. 1484 5 The unitless dimensions on the right side would require a note in the title block that says. Units mm When a tolerance is on both sides of a dimension it is called a bilateral tolerance in. this example it would be 1500 10 A tolerance on a single side of a dimension is called a unilateral. tolerance as shown in the right example in the figure These are also called minimum and maximum. metal conditions Consider a part to fit in a gap of 1501 mm The maximum metal condition cannot be. over 1500 mm but the minimum metal condition could be as small as 1490 The number of significant. APPENDIX B Technical Drawing e9,1495 mm 1500 15,FIGURE B 9. Dimensions and tolerances, Through Holes these are cut all the way Blind Holes these holes stop part way through.
through an object an object, Tapered Holes Use for part alignment Counterbored Holes Use to allow the head of a. screw to sit below the material surface,FIGURE B 10. figures in a tolerance also dictates the precision of the parts in this case up to 0 5 mm Individual toler. ances can be adjusted by adding or removing significant figures Of course larger tolerances decrease. the cost of manufacturing, Conventions for part holes are illustrated in Figure B 10 Through holes are cut so that they pass. completely through the part whereas blind holes do not Blind holes are made with drills that leave a. conical shape at the hole bottom it should be drawn for accuracy A tapered hole will be used to help. align a shaft as it enters the hole The counter bored hole has an extra pocket cut so that the head of. the bolt or screw will be beneath the surface of the material There are many more hole types that can. be found on tool manufacturers websites, When doing cross section drawings the materials are sometimes represented with a cross hatch. pattern as shown in Figure B 11 These notations are particularly useful when dealing with assem. blies of dissimilar materials The figure also contains a number of abbreviations for part features. For example if an iron piece is to be case hardened on one face carbon infused a leader line would. point to the face and indicate HDN,e10 APPENDIX B Technical Drawing.
Aluminum Cast iron and Steel and bronze brass and Zinc lead and. magnesium and malleable iron wrought iron copper alloys. related alloys,Abbreviation Description,CBORE counter bore. CSK countersink,DIA diameter,HDN case harden,LH left hand. NC national course,NF national fine,Rc Rockwell C hardness. RH right hand,THD thread s,TIR total indicated runout. TPI threads per inch,UNC unified national course,UNF unified national fine.
FIGURE B 11,Material and feature indicators, B 12 Why would a dimension include two or three numbers. B 13 How can a blind hole be changed to a through hole. B 14 Where are phantom lines normally used, B 15 What does LH normally mean on a threaded hole. B 16 Add the necessary dimensions and lines to the three view drawing shown here Use a ruler. scale to determine the dimensions,APPENDIX B Technical Drawing e11. B 4 Professional drawing practices, A simple drawing may be a single page in a manual or data sheet More extensive drawings will come. in a package with multiple pages Larger drawing packets are like any document they have a variety. of content and features for explanation and organization Drawing packets often include the following. Higher level, l A bill of materials BOM that lists all of the drawings and purchased parts.
l Assembly and subassembly drawings, l Assembled views of subassembly and the final assembly. l Surveyor plots,Specific details, l A detailed drawing on a separate sheet with a separate title block for each part. l Supplier drawings including purchased parts,l Modified purchased parts. l Electronic media with solid model files, The BOM lists the various components in the design Each part that has a drawing should appear. in the BOM by name The BOM will also include purchased parts The group responsible for manu. facturing fabrication or construction will use the BOM to order materials and plan for building the. design For assemblies the BOM may appear on the same page and use numbers to show part position. and assembly order BOMs normally include details such as. l All part numbers,l All part names,l The quantity of each part required.
l Raw materials such as metal stock,l Supplier sources and part numbers. Each drawing must have a title block or equivalent A title block clearly describes the draw. ing with enough information to identify the part identify the designer and identify other important. details The block often appears in the bottom right side of the drawing in a large easy to read font. In more formal design control systems these may also include tracking details Common contents of. the title block includes,l Company name and division if applicable. l Machine or department name,l Part name,l Drawing number. l Part number,l Number of parts required, l Scale e g 1 2 if 5 cm on the drawing is 10 cm on the part. l Drafter name and date,l Drawing checker name and date.
l Material,l Default tolerances,e12 APPENDIX B Technical Drawing. l Finishing details such as coatings,l Default units for all dimensions. Completed drawings will normally be checked by another engineer or an experienced fabricator. Sometimes the review occurs in a design review meeting where others look at the design details and. suggest corrections and additions Typical problems found in the process are listed. l Within standards Legal and corporate, l Clarity All descriptions dimensions etc should be well understood. l Completeness Sufficient dimensions etc should be present for production. l Redundancy Redundant information should be eliminated unless essential. l Manufacturability The cost and feasibility of production should be considered e g are tolerances. sufficient excessive Are other steps adequate for product life. l Are surface finishes coatings and supplemental operations suitable for the design. Many industries have strict controls concerning designs including medical aerospace defense. and automotive Such controls require that the drawings are always current and this is achieved with. formal systems of document control In such environments each drawing is given a revision number. that is used to track the current design Any drawing with a previous revision number is removed. from circulation These updated drawings are normally accompanied by an engineering change notice. ECN which indicates those features that have been changed Systems that deal with public safety. will often carry these requirements,B 17 Why should drawings be numbered. B 18 How would a coating of pink paint be indicated on a drawing. B 19 Could a BOM be included with a design package. B 20 List six items that could be found in a drawing title block. B 5 Assembly drawings, Examples of exploded and section assembly views are shown in Figure B 12 The purpose of these.
drawings is to show how all of the parts in a design are combined The examples show a shoulder bolt. bushing two washers a nut and a base piece the container wall The section view Figure B 12 a. shows where the parts should be after assembly The exploded view Figure B 12 b shows how the. parts are assembled using a line from the bolt through the parts into the nut A design package may. contain either of these drawings or something similar based on the needs A BOM is provided to list. all of the parts and numbers which in turn are labeled on the drawings. Hidden lines dimensions tolerances and fine details are normally omitted from these diagrams. However notes will be added if they are important for assembly or fabrication of the parts The exam. ple drawings in the figure both indicate that an adhesive is to be applied to the nut bolt thread a com. mon practice to prevent unwanted loosening,APPENDIX B Technical Drawing e13. 1 Assembly,Section View,Assembly View,Use adhesive on. threads 5 2,Bill of Materials,Part No Part Description. 1 Shoulder Bolt,2 Washer qty 2 Use adhesive on,4 Nut threads. 5 Container Wall,FIGURE B 12, Assembly drawing examples showing a section view and b exploded view.
In more extensive designs there may be assembly drawings for various subassemblies and then a. higher level assembly drawing for the subassemblies Designs with small details within large dimen. sions may also use an inset bubble with a finer level of detail for critical sections These drawings. can be time consuming to create manually but CAD software provides many tools for creating these. quickly Designers will also use the assembly capability to verify that assembly is possible. B 21 Why would a set of drawings come with an assembly view. B 22 What type of assembly view shows the final component locations and contact points. B 23 Sketch an assembly view for a disposable coffee cup. e14 APPENDIX B Technical Drawing,B 6 Special part views. In any drawing or graph we want to use as much of the paper as possible to show the details Figure B 13. shows two methods for shortening long parts so that the remaining portion can be drawn larger with more. detail The S break is commonly used for round objects while the Z break is used for flat and rectangular. pieces Other break lines can be identified by the rough nonstraight shapes. Section views are used to see internal features of a part to help visualize inner features or when. the internal features cannot be shown with hidden lines An example of a section drawing is shown in. Figure B 14 The line plane for the section is indicated with the heavy dashed line The arrows indi. cate which direction the view will look features in the other direction will not be seen The section. name is indicated with the letters A at the ends of the section line In this example the section is not. essential but it helps illustrate the internal geometry The section view is an extra drawing in addition. to the three view drawings, Section lines do not need to be straight The example in Figure B 15 shows a section line that only. exposes the top half of the round part Without the section view this part would be much harder to. understand Unlike the previous example where the section view was separate this one has been incor. porated into one of the normal views In the top half the section details are shown with diagonal and. visible lines The bottom half of the right view shows external edge lines and internal hidden lines. Figure B 16 shows another section view for a large round part possibly an induction motor stator. Internal features of the stator are shown by removing part of the surface The section is indicated by a. nonstraight cut line This approach does not require the addition of another section view Without the. exposed section the drawing would not be sufficient for geometrical understanding. FIGURE B 13,Breaking parts in drawings,APPENDIX B Technical Drawing e15. Section A A,FIGURE B 14,Section views,FIGURE B 15,Partial section views.


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