Sacramento City College Engineering Design Technology

Surface Developments 1

Surface Developments

Sacramento City College

Engineering Design Technology

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A surface development is a full-size layout of an object made on a single flat plane. Refer to Figure 18-1.

Example: bookcover

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Surface developments are also called: Stretchouts

Developments

Surface developments are an important part of industrial drafting.

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Many different industries use surface developments.

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These items are made using developments. Pipes.

Air conditioning ducts.

Aircraft.

Automobiles.

Storage tanks.

Cabinets.

Boxes and cartons.

Frozen food packages.

Many other items.

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A surface development is first drawn as a pattern.

The pattern is then cut from flat sheets of material, that can be folded, rolled or otherwise formed into the required shape.

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Pattern materials include: Paper.

Cardboard.

Plastics and films.

Metals.

Wood.

Fiberboard.

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The packaging industry uses surface developments extensively.

Creating packaging requires engineering and artistic skills.

Each package must meet many requirements. The package must protect the contents.

It must look attractive for sales appeal.

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Packaging must also protect the contents during shipping.

Packaging must also be durable. One use package.

Multiple use package.

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Designers use many different materials in various thicknesses. Thin paper stock.

Medium thickness paper stock.

Material can be folded easily into the desired shape. Tabs.

Glueless tabs.

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Packages require allowances for the material thickness.

Bend marks are shown with a circle on the fold line.

Refer to Figure 18-4.

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Figure 18.4


Sheet Metal Pattern Drafting

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Many different metal objects are made from sheets of metal that are laid out, cut and formed into the required shape and then fastened together. Computer cases

Automobiles

Air conditioning ductwork

Toys

File cabinets

Etc.

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For each sheet-metal object to be produced, two drawings are usually made. Pictorial drawing.

Shows the product as a picture.

Development or pattern. Used to actually cut out the sheet metal which is

then bent and assembled into the final shape

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Pictorial drawing Shows the appearance of the final product.

Development or pattern Shows the shape of the object as a flat

sheet, that after rolling, folding and fastening, will form the finished object.

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Figure 18-6

Pictorial

Drawing

Pattern

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Many thin metal objects are formed by die stamping.

Die Stamping Is pressing a flat sheet into the desired

shape under great pressure.

The flat stock is inserted into a die, which is a mirror image of the final product.

Many thin metal objects are die stamped.

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Die Stamping examples Brass cartridge cases.

Household utensils.

Wheelbarrows.

Automobile fenders, hoods, doors.

Aircraft parts.

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Making sheet-metal objects can involve many operations.

All are done with machines.


Most industrial plants now use mass production with highly complex automatic machines.

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Sheet Metal Operations Squaring.

Folding.

Wiring.

Box and Pan Brake.

Burring.

Forming.

Setting-down machine.

Turning machine.

Doubling-seaming machine.

Beading machine.

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Shaping

Shaping: Shearing

Cutting

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Shaping

Shaping: Bending

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Shaping

Shaping: Folding

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Fastening: Riveting

Seaming

Soldering

Welding


Seams and Laps

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Seams and Laps

Knowledge of Wiring.

Hemming.

Seaming.

is also required.

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Wiring involves reinforcing open ends of articles by

enclosing a wire in the edge.

See Figure 18-11A.

The drafter must add a band of material equal to 2.5 times the wire diameter.

Hemming Method of stiffening edges

Refer to Figure 18-11B and C.

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Wiring

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Seaming

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Seaming


Pattern Development

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Sheet Metal patterns are developed using surface geometry.

There are two classes of patterns: Plane.

Flat, rectangular, non-spherical objects

Curved. Spherical objects.

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Plane surfaces: Sides of a cube.

Top and bottom of a cylinder.

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Curved surfaces: Surfaces that can be rolled in contact with a

plane surface.

Side of a cylinder.

Side of a cone.

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Double curved surfaces: Spheres.

Spheroids.

Exact surface developments cannot be made for objects with double-curved surfaces. Drafters can make approximations.

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Double-Curved Approximations

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Pattern for a Cube

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Pattern for a Cube

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Making Paper Patterns

Patterns can be laid out on stiff drawing paper.

Cut out pattern and fold to make a solid.

Secure the joints with tape.


Pattern Line Development

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Parallel Line Development

Parallel-Line Development is a simple way of making a pattern by drawing the edges of an object as parallel lines. Refer to Figure 18-9 and 18-12.

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Prisms

Patterns for prisms are made by parallel-line development.


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Parallel Line Development Procedure

1. Draw the front and top views full-size. Label the points.

Refer to Figure 18-14A.

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2. Draw the stretchout line (SL). The stretchout line shows the full length of

the pattern.

Find the lengths of sides 1-2, 2-3, 3-4, 4-1.

Measure these lengths off on SL.

Refer to Figure 18-14B.

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3. At points 1, 2, 3, 4 and 1 on the stretchout line, draw vertical crease lines. Make them equal in length to the height of

the prism

Refer to Figure 18-14C.

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Figure 18.14C

Vertical lines = prism height

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4. Project the top line of the pattern from the top of the front view. Make it parallel to SL.

Darken all outlines until thick and black.

Refer to Figure 18-14D.

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Figure 18.14D

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5. Add the top and bottom to the pattern by transferring distances 1-4 and 2-3 from the top view. Refer to Figure 18-14E.

Add laps or tabs as necessary for assembly of the prism.

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Figure 18.14D

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Figure 18.15


Cylinder Patterns

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Cylinder Patterns

In the pattern for cylinders, The stretchout line is straight.

The stretchout line is equal in length to the circumference of the cylinder.

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Cylinder Patterns

If the base of the cylinder is perpendicular to the axis, its rim will roll out to form the straight line.

If the base is not perpendicular to the axis, You will have to make a right section to get

the stretchout line.

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Figure 18.16

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Truncated Cylinder

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Truncated Cylinder Patterns

To develop a truncated cylinder, imagine that the cylinder is a many-sided prism.

Each side forms an edge called an element.

Because there are so many elements, they seem to form a smooth curve on the surface of the cylinder.

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Cylinder Patterns


Mark off elements at convenient equal spaces around the circumference of the cylinder.

Then, add up these spaces to make the stretchout line.

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Figure 18.17

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Cylinder Patterns


This figure is a pictorial view of a truncated right cylinder Notice the imaginary elements.

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Figure 18.18

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Cylinder Patterns

Figure 18-19 shows the steps to draw the pattern.

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Figure 18.19


Drawing Truncated Cylindrical Patterns

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1. Draw the front and top views full size. Divide the top view into a convenient number

of equal parts.

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2. Begin the stretchout line. You will determine its actual length later.

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3. Using dividers, find the distance between any two consecutive elements. Mark off this distance along SL.

Repeat for each elements in the top view, along the SL.

Label each point.

From each point, draw a vertical construction line upward.

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4. Project other lines downward from the elements on the top view to the front view. Label the points where they intersect the

front view.

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5. From the intersection points, project horizontal construction lines toward the development.

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6. Locate the points where the horizontal construction lines intersect the vertical lines from the SL. Connect these points in a smooth curve.

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7. Darken outlines and add laps as necessary.

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Since the surface of a cylinder is a smooth curve, the pattern will not be completely accurate.

The pattern was made by measuring distances on a straight line rather than on a curve.


Right Rectangular Pyramids

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Figure 18-29

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Figure 18-29

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Figure 18-30


Triangulation

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Triangulation

Triangulation is a method used for making approximate developments of surfaces that cannot be developed exactly. Maps

Approximations of spherical surfaces

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Triangulation

In Triangulation the surface is divided into triangles, by finding the true length of the sides.

The triangles are “connected” to form the object.

The triangles approximate the shape of the object.

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Triangulation

Maps of the Earth are often represented using triangulation.


Transition Pieces

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Transition Pieces

Transition pieces are used to connect pipes of different shapes to pipes of other shapes.

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Transition Pieces

Transition pieces have a surface that is a combination of different forms. Planes

Curves


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Transition Pieces

Figure 18-37 shows the making of a transition piece.

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Transition Pieces

Figure 18-39 shows a transition piece to connect a round pipe with a rectangular pipe.


Drawing a Transition Piece

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Transition Pieces

Also known as a square to round, this transition piece is a duct component that provides a change in shape from square or rectangular to round.

Transition pieces may be designed to fit any given situation, but the pattern development technique is always as follows.

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Transition Pieces

Accuracy and the use of a number system is very important.

Do all lay-out work using construction lines FIRST, then darken in object lines when you know your figure is correct.

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Figure 18-55

Assignment

Page 18-55A

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Pattern Development

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Transition Piece - Step 1

Step 1 Draw the top and front views.

Divide the circle in the top view into twelve

equal parts.

Connect the points in each quarter of the

circle to the adjacent corner of the square.

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Project the same corresponding system to the front view.

Number and letter each point in each view as shown in Figure 24-55.

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The transition piece shown in Figure 24.55 is made up of a series of triangles 1,A,D.

1,2,A.

2,3,A.

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The development progresses by attaching the true size and shape of each triangle together in order.

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This technique is known as triangulation.

There is no stretch-out line.

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Each element of the development must be in true length.

Establish the true-length diagram using revolution as shown in Figure 24.56.

Only one set of true-length elements is required because the given problem is a right transition piece (symmetrical about both axes).

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Figure 24.56

Establishing

True Length

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Establishing

True Length

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Begin the pattern development on a sheet in an area where there is a lot of space.

Start with the true size and shape of triangle 1,A,D.

The true lengths of 1-A and 1-D are the same and may be found in the true-length diagram.

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The true length of A-D is in the top view (See Figure 24.57.)

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Work both ways from triangle 1,A,D in Figure 24.57 to develop the adjacent triangles.

From points A and D draw arcs equal to A-2 and D-12, respectively.

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Set a compass for the distance from 1-2.

Keep this compass setting as it is used several times.

With this setting, scribe two arcs from point 1 that intersect the previously drawn arcs.

These intersections are points 2 and 12.

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Connect points 2-A and 12-D.

Do not connect points 1,2 and 12 yet.

(See Figure 24.58.)

Do all work with construction lines until complete

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Continue the same procedure, working both ways around the transition piece until the entire development is complete.

Every triangle must be included

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The pattern will end on both sides with the element 7-X, which is true length in the front view.

The two final triangles are right triangles, because each is half of the full side that is an equilateral triangle.

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Every line transferred from the views to the pattern must be true length.

Use the numbering system be used to avoid errors.

When all points have been established, the outline may be darkened.

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When all points have been established, the outline may be darkened.

A series of points form the inside curve.

Connect these points with an irregular curve.

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If any point is out of alignment with the others, you have made an error at this location.

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Error at this point

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Sacramento City College Engineering Design Technology