1 HVACR116 – Trade Skills Sheet Metal Drawings
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IntroductionIntroduction
• Surface developmento 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 fastenedo Done manually or by CAD/CIM or both
• Surface developmento 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 fastenedo Done manually or by CAD/CIM or both
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Pattern Development ProcessesPattern Development Processes
• Flat-form pattern in sheet metal worko Developed by:
Parallel line development Radial line development Triangulation
• Transition pieceso Parts connecting pipes or openings of different sizes and
shapes
• Flat-form pattern in sheet metal worko Developed by:
Parallel line development Radial line development Triangulation
• Transition pieceso Parts connecting pipes or openings of different sizes and
shapes
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Parallel Line DevelopmentParallel Line Development
• Pattern drawn full size o Using parallel lines for width, height, and depth
• If cylindrical and truncatedo Divide cylinder circle into equal elementso Height transferred to stretchouto 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 truncatedo Divide cylinder circle into equal elementso Height transferred to stretchouto May develop pattern for more pieces of same diameter
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IntersectionsIntersections
• Line of intersection (cutting plane line)o Where several sheet metal parts joino May be straight or curved lineso 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 joino May be straight or curved lineso Developed by:
Transfer of true length heights from successive elements to plane surface layout
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Bend, Seam, and Lap AllowancesBend, Seam, and Lap Allowances
• Bend allowanceo Varies based on:
Sheet material, thickness, bend form and sizeo 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 allowanceo Varies based on:
Sheet material, thickness, bend form and sizeo 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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Precision Sheet Metal Parts ProductionPrecision Sheet Metal Parts Production
• Instrument, gage, electronic, and precision equipment o Requires layouts and parts produced to precise machine
shop standardso Blanked, perforated, formed, and trimmed using punches
and dieso 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 standardso Blanked, perforated, formed, and trimmed using punches
and dieso Manually or computer-programmed o Produced on numerical control machines
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Precision Sheet Metal Parts Production (cont’d.)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