Misinterpretation of Scale

COMMON ERRORS ABOUT THIS DOCUMENT Thisdocument highlightssomeofthe commonly observed errors.You areurged toreview the lecture notesandengineering drawingbooksto strengthen yourunderstanding ofthe : Elements of engineering drawings, Projection Systems, Dimensioning. COMMON ERRORS Incorrect Projection System. Using incorrect Line Types. Incorrect interpretation of SCALE. Incorrect Dimensioning. Incorrect projections of object features. Incorrect drawing sheet size. Incorrect/Incomplete information on drawings. INCORRECT PROJECTION SYSTEM COMMON ERRORS Placing the views at random locations. Placing the left side view on the right of the front view. Indicating wrong projection system. For example, placing a symbol for FIRST -ANGLE on a drawing that was actually drawn in THIRD -ANGLE. SAMPLE QUESTION # 1 On a sketching paper / drawing sheet, draw the three orthographic views (FRONT, TOP and left SIDE) of the following object. Us a SCALE of 1:1 The arrow indicates the direction of FRONT view. ALL DIMENSIONS ARE INMILLIMETRES. SAMPLE QUESTION # 2 On a sketching paper / drawing sheet, draw three orthographic views (FRONT, TOP, and SIDE) to describe the following part. Follow third angle projection. Use a scale of 1:2. The arrow indicates the direction of FRONT view. ALL DIMENSIONS ARE INMILLIMETRES INCORRECT PROJECTION SYSTEM INCORRECT Placement of views do not conform to the given projection system. X INCORRECT PROJECTION SYSTEM INCORRECT Left side view is placed on the right side of the Front view. This orientation indicates that the FRONT and TOP views are in THIRD-ANGLE, whereas the FRONT and LEFT SIDE are in FIRST -ANGLE projection. FRONT TOP LEFT SIDE X INCORRECT PROJECTION SYSTEM CORRECT THIRD-ANGLE PROJECTION SYSTEM USING INCORRECT LINE TYPES COMMON ERRORS Using continuous lines as Centre Lines. Using dimension lines without arrow heads. Using extension lines and dimension lines that are thicker than object lines. Examples of these errors are shown on the following slides. USING INCORRECT LINE TYPES INCORRECT Continuous line has been used as a centre line. X USING INCORRECT LINE TYPES CORRECT USING INCORRECT LINE TYPES Object lines, dimension lines, and extension lines have the same thickness.Dimension lines and extension lines are thicker than the object lines. INCORRECT XX USING INCORRECT LINE TYPES CORRECT INCORRECT INTERPRETATION OF SCALE COMMON ERRORS Using 1:2 as enlargement SCALE. Using 2:1 as reduction SCALE. Indicating wrong scale on the drawing. For example, the drawing was drawn on 1:1 but the scale shown was 2:1 or 1:2. Using non-standard SCALES. For example, 1.5:1, 3:4 ERRORS INDIMENSIONING COMMON ERRORS Derivingdimensions. Not indicating direct dimensions. Dimensioning to hidden features. Indicating redundant dimensions . Multiplying / dividing the dimension values by the SCALE factor. Not using extension lines. Placing dimensions too close to the object lines. Placing dimensions inside the views. Not placing centre lines to indicate circular features. Examples of these errors are shown on the following slides. ERRORS IN DIMENSIONING INCORRECT Derived dimensions. Sizes 35 and 45 are unnecessary as they were not shown on the given object. Also, a direct dimension (size 50) is missing. X X ERRORS IN DIMENSIONING CORRECT ERRORS IN DIMENSIONING INCORRECT Breaking the extension line or leaving gaps is a poor practice. Just extend the centre line without leaving any gaps. GAPS X X ERRORS IN DIMENSIONING CORRECT ERRORS IN DIMENSIONING Redundant dimensionDerived dimension. Also, a direct dimension (size 55) is missing. INCORRECT ERRORS IN DIMENSIONING CORRECT ERRORS IN DIMENSIONING INCORRECT Dimensions have been placed where the features appear as hidden. X X Dimensioning to hidden features. ERRORS IN DIMENSIONING CORRECT ERRORS IN DIMENSIONING INCORRECT This drawing is drawn on a SCALE of 1:2. Dividing the dimension values by the SCALE factor is incorrect. X X X X X XX X ERRORS IN DIMENSIONING CORRECT ERRORS IN DIMENSIONING INCORRECT The dimensions have been placed without using extension lines. This style indicates that the dimensions are NOT linked to the features . X ERRORS IN DIMENSIONING CORRECT ERRORS IN DIMENSIONING INCORRECT The dimension lines have been used without ARROW HEADS!!!!! X ERRORS IN DIMENSIONING CORRECT ERRORS IN DIMENSIONING INCORRECT Dimensions have been placed inside the view. X X X ERRORS IN DIMENSIONING CORRECT ERRORS IN DIMENSIONING INCORRECT Dimensions have been placed too close to the object. X X X ERRORS IN DIMENSIONING Maintain a line spacing of 12 15 mm CORRECT INCORRECT DRAWING SHEET SIZES COMMON ERRORS Selecting very large or too small sheet size. W orkout the drawing sheet size according to the size of the object and the drawing scale. Badly cluttered drawings. Leave a reasonable space between views. Scaling down the title blocks. Title blocks are not scaled up / down. INCORRECT PROJECTIONS COMMON ERRORS Not indicating fillets and rounds. Indicating lines where round surfaces smoothly join the flat surfaces. Not indicating hidden details. INCOMPLETE / INCORRECT INFORMATION ON DRAWINGS COMMON ERRORS Not indicating the dimensional units. Including NOT TO SCALEphrase on the drawing, whereas a SCALE was also indicated on the same drawing. Not including the DO NOT SCALE warning. Repeating the same information. For example, mentioning both the SIand ALL DIMENSIONS IN MILLIMETERS. Placing information at wrong locations in the title block. For example, mentioning company name in the area, which is designated for the drawing title. Using lower case letters.