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116- Trade Skills 116- Trade Skills

Hems, Edges, and SeamsHems, Edges, and Seams

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• Sheet metal pieces, such as ductwork, down spouts, and washing machine housings, begin with a flat pieces of metal.

• Patterns of the stretched out pieces are transferred or made directly on to the flat metal.

• These patterns include allowances, or additional material, for hems, seams, and edges.

• Sheet metal pieces, such as ductwork, down spouts, and washing machine housings, begin with a flat pieces of metal.

• Patterns of the stretched out pieces are transferred or made directly on to the flat metal.

• These patterns include allowances, or additional material, for hems, seams, and edges.

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• The amount of allowance is determined by the thickness of the metal, the radius of the bend, and the type of bend being made.

• Once outlined on the metal piece, the pattern is cut out.

• Hems, seams, and edges are important in the fabrication of the metal pieces. – They join opposite ends of a pattern to make a

complete piece. – They can also join completely separate pieces.

• The amount of allowance is determined by the thickness of the metal, the radius of the bend, and the type of bend being made.

• Once outlined on the metal piece, the pattern is cut out.

• Hems, seams, and edges are important in the fabrication of the metal pieces. – They join opposite ends of a pattern to make a

complete piece. – They can also join completely separate pieces.

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HemsHems

• A hem is a folded over edge on a piece of metal.

• It is used to finish off rough, sharp ends of metal sheet and to strengthen and improve the appearance of a project.

• Allow about ¼” for the hem.– When using metal heavier

than 22 gage, increase the hem to 5/16” or 3/8”

• A hem is a folded over edge on a piece of metal.

• It is used to finish off rough, sharp ends of metal sheet and to strengthen and improve the appearance of a project.

• Allow about ¼” for the hem.– When using metal heavier

than 22 gage, increase the hem to 5/16” or 3/8”

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• A double hem is a single hem, repeated.

• A double hem provides much greater strength than single hems.

• Double hems are generally 5/16” or 3/8.

• A double hem is a single hem, repeated.

• A double hem provides much greater strength than single hems.

• Double hems are generally 5/16” or 3/8.

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• Hems can be made using a bar fold or a brake. – A bar fold can make a hem in one motion. – A brake requires two motions.

• One to bend the metal• One to press the metal flat.

• Hems can be made using a bar fold or a brake. – A bar fold can make a hem in one motion. – A brake requires two motions.

• One to bend the metal• One to press the metal flat.

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SeamsSeams

• Seams are used to fasten sheet metal sections together using locks, rivets, screws, brazing, or soldering.

• They can be made by hand, on a brake, or on a bar fold.

• The type of seam made and the fastening method depends on the type of metal, its thickness, and its fabricating machinery available to the worker.

• Seams are used to fasten sheet metal sections together using locks, rivets, screws, brazing, or soldering.

• They can be made by hand, on a brake, or on a bar fold.

• The type of seam made and the fastening method depends on the type of metal, its thickness, and its fabricating machinery available to the worker.

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• A wide variety of seam types have been designed for use on sheet metal.

• About 20 types of seams are used in ductwork construction and for other purposes.

• A wide variety of seam types have been designed for use on sheet metal.

• About 20 types of seams are used in ductwork construction and for other purposes.

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Variety of seamsVariety of seams

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Pittsburgh SeamPittsburgh Seam

• The Pittsburgh is commonly used in sheet metal shops.

• The seams has two parts:– A single, 90 degree lock and a pocket lock.

• The single lock is inserted into the pocket lock, after which the edge of the pocket lock is folded down to seal the seam.

• The Pittsburgh is commonly used in sheet metal shops.

• The seams has two parts:– A single, 90 degree lock and a pocket lock.

• The single lock is inserted into the pocket lock, after which the edge of the pocket lock is folded down to seal the seam.

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• Pittsburgh seams are often used in HVAC ductwork.

• They can be formed on all gage metals, from 16 to 40 gage.

• This seam is easy to form on the hand brake or a Pittsburgh machine.

• A distinct advantage to the Pittsburgh seam is that it can be formed on curves.

• Pittsburgh seams are often used in HVAC ductwork.

• They can be formed on all gage metals, from 16 to 40 gage.

• This seam is easy to form on the hand brake or a Pittsburgh machine.

• A distinct advantage to the Pittsburgh seam is that it can be formed on curves.

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Steps to make a Pittsburgh seamSteps to make a Pittsburgh seam

Step 1 Step 2

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Dovetail SeamsDovetail Seams

• The dovetail seam is used to primarily on round or elliptical pipes. It is seldom used on rectangular.

• There are three types of dovetail seams. – Plain– Beaded– Flanged

• The dovetail seam is used to primarily on round or elliptical pipes. It is seldom used on rectangular.

• There are three types of dovetail seams. – Plain– Beaded– Flanged

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• The plain dovetail seam is used to join a collar and separate flange. – This seam is made without rivets, screws, solder.

• Instead, tabs are cut at the end of the collar and every other tab is then bent down.

• The separate flange is then added, with the bent tabs holding it in place.

• The remaining tabs are then bent over the flange to secure it.

• The plain dovetail seam is used to join a collar and separate flange. – This seam is made without rivets, screws, solder.

• Instead, tabs are cut at the end of the collar and every other tab is then bent down.

• The separate flange is then added, with the bent tabs holding it in place.

• The remaining tabs are then bent over the flange to secure it.

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Slip Joint SeamSlip Joint Seam

• A slip joint seam consists of the edges to be joined and a drive clip that joins them.

• The edges are turned to form pockets. – The edge on the drive

clip, made from a separate piece of metal, are also turned to make pockets.

• A slip joint seam consists of the edges to be joined and a drive clip that joins them.

• The edges are turned to form pockets. – The edge on the drive

clip, made from a separate piece of metal, are also turned to make pockets.