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HVACR116 – Trade Skills

Sheet Metal DrawingsSheet 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

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Circuit-Dial Cover SCD 7 (BP-32)

Assignment-Unit 32Assignment-Unit 32

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