1 HVACR116 – Trade Skills Sheet Metal Drawings

2 Introduction Surface development o Laying out each section in full size as single form on flat, plane surface  Called template, stretchout, or pattern o Cut to size and may be shaped o Matching surfaces may need to fastened o Done manually or by CAD/CIM or both Surface development o Laying out each section in full size as single form on flat, plane surface  Called template, stretchout, or pattern o Cut to size and may be shaped o Matching surfaces may need to fastened o Done manually or by CAD/CIM or both

3 Pattern Development Processes Flat-form pattern in sheet metal work o Developed by:  Parallel line development  Radial line development  Triangulation Transition pieces o Parts connecting pipes or openings of different sizes and shapes Flat-form pattern in sheet metal work o Developed by:  Parallel line development  Radial line development  Triangulation Transition pieces o Parts connecting pipes or openings of different sizes and shapes

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5 Parallel Line Development Pattern drawn full size o Using parallel lines for width, height, and depth If cylindrical and truncated o Divide cylinder circle into equal elements o Height transferred to stretchout o May develop pattern for more pieces of same diameter Pattern drawn full size o Using parallel lines for width, height, and depth If cylindrical and truncated o Divide cylinder circle into equal elements o Height transferred to stretchout o May develop pattern for more pieces of same diameter

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7 Intersections Line of intersection (cutting plane line) o Where several sheet metal parts join o May be straight or curved lines o Developed by:  Transfer of true length heights from successive elements to plane surface layout Line of intersection (cutting plane line) o Where several sheet metal parts join o May be straight or curved lines o Developed by:  Transfer of true length heights from successive elements to plane surface layout

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9 Bend, Seam, and Lap Allowances Bend allowance o Varies based on:  Sheet material, thickness, bend form and size o Appear as dimensions for straight, right-angle, and open or closed bends o Drawings of precision sheet metal parts  Show bend line for starting of bend and dimension giving allowance Bend allowance o Varies based on:  Sheet material, thickness, bend form and size o Appear as dimensions for straight, right-angle, and open or closed bends o Drawings of precision sheet metal parts  Show bend line for starting of bend and dimension giving allowance

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11 Precision Sheet Metal Parts Production Instrument, gage, electronic, and precision equipment o Requires layouts and parts produced to precise machine shop standards o Blanked, perforated, formed, and trimmed using punches and dies o Manually or computer-programmed o Produced on numerical control machines Instrument, gage, electronic, and precision equipment o Requires layouts and parts produced to precise machine shop standards o Blanked, perforated, formed, and trimmed using punches and dies o Manually or computer-programmed o Produced on numerical control machines

12 Precision Sheet Metal Parts Production (cont’d.) Ordinate drawings o Commonly used for producing precision sheet metal parts Ordinate dimensions o Referenced to zero datums o Provide position and size dimensions  For production on NC or CNC equipment Ordinate drawings o Commonly used for producing precision sheet metal parts Ordinate dimensions o Referenced to zero datums o Provide position and size dimensions  For production on NC or CNC equipment

13 Circuit-Dial Cover SCD 7 (BP-32) Assignment-Unit 32

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