CHAPTER 20



CHAPTER 27

INTERSECTIONS

Learning Objectives

Upon completion of this chapter you will be able to accomplish the following:

1. Determine the line of intersection or common line of joined shapes so that they may

be graphically described and economically produced.

2. Utilize edge view and cutting plane methods in order to locate points of intersection.

3. Develop an understanding of the importance of auxiliary views in solving for

intersections.

4. Master the ability to produce conic sections while identifying resulting shapes.

5. Develop an understanding of the CAD system's capacity for surface and solid

modeling to produce solutions to intersection problems.

6. Demonstrate familiarity with CAD commands used to generate intersections

27.1 Introduction

The design and engineering of products and systems will involve line, planes, and solids that intersect. Cubes, prisms, pyramids, cylinders, cones, spheres, etc., and their intersecting variations are just a few of the many forms used in engineering design work. Part of the responsibility of a designer is to establish simple and complex forms in such a manner that the result is a functional, producable product. A necessary step in this process is the determination of the intersection of the various shapes so that they can be graphically described and economically manufactured.

Piping systems [Fig. 27.1(a)] include a vast array of intersecting shapes and forms. A piping system for a refinery can be created in 3D using a solid modeling CAD/CAM system [Fig.27.1(b)]. The pumping station shown in Figure 27.1(c)is another example of a subsystem designed with a solid modeling package. Instersecting pipes, nozel and vessel intersections and a wide variety of equipment intersections are all found on the typical process piping project. Besides piping, intersections are also important for other engineering fields. The scale model of the clean room in Figure 27.2 has a numder of intersections. The air filtration system is composed of intersecting HAVC sheet meal ducting, and the ducting system intersect walls and floors. The turboprop solid model in Figure 27.3 is an example of an extremely complex form (the blades) intersecting a hub. The tilt stand transport shown in Figure 27.4 uses intersecting braces in it’s construction. This figure also shows a number of cylinder to cylinder intersections.

Intersections can be solved using manual or automated methods, or using construction techniques developed for manual drafting but applied by a 2D CAD system. The intersection of shapes is established with simple commands. Using a 3D CAD system gives the designer the ability to pass a plane through a part at any orientation to create any desired cross section for detail drawings.

The intersection of two shapes forms a line of intersection or common line. A basic step in finding the line of intersection between two geometric shapes is to determine the intersection of a line and a plane (piercing point), which was presented in the last chapter. The points of intersection are located by the projection of an edge view of the plane and/or the introduction of cutting planes of known orientation. These two methods may be utilized separately or together, depending on the requirements of the problem.

27.2 Intersection of Planes

The intersection of two or more planes can be determined by finding the edge view of one of the planes. Where any two lines on one plane pierce the edge view of any plane, they will determine the endpoints of the line of intersection. Both lines and planes can be considered unlimited in size or length for construction purposes. Therefore, both given planes and their line of intersection can be extended as required. The actual intersection of two defined planes will have a limited line of intersection that must be common to both planes.

27.2.1 Intersection of Two Planes

To establish the intersection of two planes, it is necessary to find two points common to both planes. These points of intersection form a straight line. In Figure 27.5 the line of intersection and correct visibility are required. The following steps were used to solve the intersection:

1. Plane 1-2-3-4 and plane 5-6-7 are given. Plane 1-2-3-4 appears as an edge in the frontal

view [Fig. 27.5(a)].

2. Lines 5-6 and 5-7 pierce the edge view of plane 1-2-3-4 at points 8 and 9, respectively [Fig. 27.5(b)].

Project these two piercing points to the horizontal view where they form line 8-9, which is the line of

intersection. Visibility is determined by inspection

27.2.2 Intersection of Two Oblique Planes (Edge View Method)

When the intersection of two oblique planes is required, an auxiliary projection showing one of the planes as an edge is needed. In Figure 27.6, oblique planes

1-2 3-4 and 5-6-7 are given. The following steps were used in the solution:

1. Lines 1-3 and 2-4 are horizontal lines [Fig. 27.6(a)]. Draw H/A perpendicular to line 2-4 and project

auxiliary view A. Plane 1-2-3-4 appears as an edge view and plane 5-6-7 is oblique in view A.

2. Line 5-7 pierces the edge view of plane 1-2-3-4 at point 8 [Fig. 27.6(b)]. Line 5-6 pierces

plane 1-2-3-4 at point 9. Project points 8 and 9 to the horizontal view where they form the

common line of intersection between the two planes, line 8-9.

3. Locate intersection line 8-9 in the frontal view by projection. The portion of the plane formed by

line 8-9 and point 5 is in general above and in front of plane 1-2-3-4; therefore, it appears visible

in the frontal and horizontal view.

27.2.3 Intersection of Two Planes (Cutting Plane Method)

The cutting plane method for finding the intersection of a line and a plane can be used to establish two common piercing points. Each piercing point is found individually and then projected to the adjacent view. Using cutting planes to solve for the piercing point of a line and a plane in each view, instead of projecting located points from view to view, is called the individual line method.

In Figure 27.7 oblique planes 1-2-3 and 4-5-6-7 are given. Their line of intersection is to be determined using the cutting plane method. Note that some lines make better cutting planes than others. Suitability is determined by trial and error. Some lines will obviously not cross the other plane and, therefore, cannot be used (unless extended). Others cross only very small parts of the other plane and may not be adequate. It may be necessary to extend a line in some cases. Also, cutting planes can be established using lines of different planes in the same view. In Figure 27.7 cutting planes are passed through different lines on the same plane. The following steps were used to solve the problem:

1. Pass a vertical cutting plane through line 1-2 in the horizontal view [Fig. 27.7(a)]. Line 1-2

represents the edge view of CP1. CP1 cuts line 4-7 at point 8 and line 5-6 at point 9. Project

points 8 and 9 to the frontal view, where they form line 8-9. Line 8-9 crosses (intersects) line 1-2

at PPA. PPA is the piercing point of line 1-2 and plane 4-5-6-7. Project piercing point PPA back

to the horizontal view.

2. Pass vertical cutting plane CP2 through line 2-3, in the horizontal view [Fig. 27.7(b)]. Line 2-3

represents the edge view of CP2. CP2 crosses line 5-6 and line 6-7 at points 10 and 11,

respectively. Project points 10 and 11 to the frontal view, where they form line 10-11. Line 10-11

crosses (intersects) line 2-3 at piercing point PPB. Project PPB back to the horizontal view.

3. Connect point PPA and point PPB to form intersection line A-B [Fig. 27.7(c)]. Visibility

is determined by applying the visibility test as shown.

27.3 Intersection of a Plane and a Prism (Edge View Method)

For the intersection of a prism and a plane an auxiliary view showing the plane as an edge is required if the plane is oblique in the given views. In Figure 27.8 the horizontal view shows the plane as an edge. Therefore the piercing points of each line (edge of the prism pierce the plane and establish the points along the line of intersection. In Figure 27.9, plane 1-2-3-4 and prism 5-6-7 are both oblique in the given frontal and horizontal views. The solution to this problem requires the projection of a view showing the plane as an edge. The intersection and correct visibility are required. The following steps were used to solve the problem:

1. Lines 1-2 and 3-4 are horizontal lines (true length in the horizontal view). H/A is drawn perpendicular

to line 1-2. Complete auxiliary view A.

2. Plane 1-2-3-4 represents the edge view of a cutting plane in view A. Plane 1-2-3-4 intersects

the prism at points 8, 9, and 10. In other words, the edge lines of the prism pierce the plane at

points 8, 9, and 10. Project all three piercing points to the horizontal view. The horizontal view of

the piercing points determines the plane section cut from the prism, which in turn corresponds to

the intersection of the plane and prism.

3. Project points 8, 9, and 10 to the frontal view. The frontal location of each piercing point can also

be fixed by transferring distances from auxiliary A along projection lines drawn from each point in

the horizontal view. This method will ensure the accurate location of the intersecting points, and

should be used to check the placement of the piercing points.

4. Visibility is determined by inspection of auxiliary view A and or the visibility test.

27.3.1 Intersection of a Plane and a Right Prism (Cutting Plane Method)

The line of intersection between two surfaces is a common line defined by connected piercing points located by the introduction of cutting planes. In Figure 27.10 the intersection of plane 1-2-3-4 and a right prism is required. The following steps were used to solve the problem:

1. Plane 1-2-3-4 and a prism defined by edge lines 5, 6, 7, and 8 are given [Fig. 27.10(a)].

2. Pass a vertical cutting plane (CP1) through the vertical plane represented by edge lines 5 and 8,

and CP2 through edge lines 6 and 7 [Fig. 27.10(b)]. CP1 intersects lines 1-4 and 2-3 at points 9H

and 10, respectively. CP2 intersects line 1-4 at point 11 and line 2-3 at point 12. Project all four

points to the frontal view where they form lines 9-10 and 11-12. Line 9-10 intersects edge lines 5

and 8 at points A and B, and line 11-12 intersects edge lines 6 and 7 at points C and D. A, B, C,

and D are the piercing points of the edge lines of the prism and the plane. Piercing points A, B, C,

and D are connected to establish the lines of intersection between the plane and prism.

3. Vertical cutting planes CP3 and CP4 could be used instead of CP1 and CP2 or as a

check [Fig. 27.10(c)].

27.3.2 Intersection of an Oblique Plane and an Oblique Prism (Cutting Plane Method)

The line of intersection of an oblique prism and oblique plane can be located by the cutting plane method. Cutting planes can be introduced at any angle, in any view. Vertical, horizontal, and front edge view cutting planes passed through existing lines are the most convenient. In Figure 27.11 the plane and the prism are given. The line of intersection is required. The following steps were used in the solution:

1. Pass vertical cutting plane CP1 through line 4 in the horizontal view.

2. CP1 intersects line 1-2 at point 8, and line 2-3 at point 7. Project points 7 and 8 to the frontal view

where they form line 7-8.

3. Line 7-8 intersects line 4 at point 14. Point 14 is the piercing point of line 4 and plane 1-2-3.

4. Project piercing point 14 to the horizontal view.

5. Pass vertical cutting planes CP2 and CP3 through line 5 and 6, respectively.

6. CP2 intersects line 2-3 at point 9 and line 1-2 at point 10. CP3 intersects lines 2-3 and 1-2 at

points 11 and 12, respectively. Project points 9 and 10 and points 11 and 12 to the frontal view where

they form lines 9-10 and 11-12.

7. Line 9-10 intersects line 5 at piercing point 13. Line 11-12 intersects line 6 at piercing point 15.

Project piercing points 13 and 15 to the horizontal view.

8. Connect all three piercing points in both views to establish the line of intersection between the plane

and the prism and solve for visibility.

Note that all three vertical cutting planes are parallel in the horizontal view and, therefore, cut parallel lines on the plane in the frontal view.

You May Complete Exercises 27.1 Through 27.4 at This Time

27.4 Cylinders

A cylinder is a tubular form that is generated by moving a straight line element around and parallel to a straight line axis. A cylinder is considered to be composed of an infinite number of elements. A right section cut perpendicular to the axis line shows the true shape of the cylinder. Most cylinders are cylinders of revolution, that is, cylinders generated by an element moving in a circle, parallel to the axis line. Cylinders are represented by their axis line and two extreme elements.

27.4.1 Intersection of a Plane and a Cylinder (Cutting Plane Method)

The line of intersection of a plane and a cylinder can be determined by passing a series of cutting planes parallel to the axis of the cylinder. Each CP cuts elements on the cylinder, which pierce the plane to form an elliptical line of intersection. Accuracy increases with the number of cutting planes employed.

In Figure 27.12 a series of vertical cutting planes is passed parallel to the axis and through the cylinder. Each cutting plane establishes two elements on the cylinder and a line on the plane. Where these related lines and elements intersect, they establish the required piercing points. The following steps were used to solve the problem:

1. Draw CP1 and CP2 parallel to the axis line (and parallel to the H/F fold line) [Fig. 27.12(a)]. CP1

intersects line 1-3 at point 4 and line 2-3 at point 5. CP2 intersects line 1-2 at point 6 and line 2-3 at

point 7. Both CPs establish an element on the cylinder. Project the elements to the frontal view along

with lines 4-5 and 6-7. Line 4-5 intersects its element at piercing point A and line 6-7 intersects its

corresponding element at point B.

2. Repeat step 1 using CP3, CP4, and CP5 [Fig. 27.12(b)]. Note that each of, these cutting planes cuts

two elements on the cylinder. Therefore, each locates two piercing points. Connect the piercing

points in sequence to form a smooth curve. Since point 2 is in front of the cylinder, lines 1-2 and 2-3

are visible, as is point B.

In Figure 27.13 the plane and the cone are oblique. A view where the plane shows as an edge is projected. In auxiliary view A, the intersection of elements on the surface of the cylinder intersect the plane and establish points along the line of intersection. Project the piercing points back into the adjacent view to find the elliptical line of intersection.

27.5 Cones

A cone is a single-curved surface formed by line segments/ elements connecting the vertex with all points on the perimeter of the base. A cone is generated by the movement of a straight line element passed through the vertex and moving around the boundary of the base. A cone generated by a right triangle rotating about one of its legs is a right cone or cone of revolution. If a right section cut from the cone is an ellipse, the cone is an elliptical cone. A cone with a circular base whose right section is an ellipse is sometimes referred to as an oblique circular cone. If a cone is cut below its vertex, it is termed a truncated cone.

27.5.1 Conic Sections

The intersection of a plane and a right cone is called a conic section. Five types of shapes can result from this intersection (Fig. 27.14).

1. Parabola A plane parallel to an extreme element of the cone, therefore forming the same base

angle, cuts a parabola (1).

2. Hyperbola A plane passed through the cone, at a greater angle than the base angle results

in a hyperbola (2).

3. Ellipse A plane that curs all the elements of the cone, but is not perpendicular to the axis, forms a

true ellipse (3).

4. Isosceles triangle A plane passed through the vertex cuts an isosceles triangle (the frontal view).

5. Circle A plane passed perpendicular to the axis forms a circular intersection. A series of horizontal

cutting planes has been in introduced in the frontal view, which project as circles in the horizontal

view (Fig. 27.14).

The intersection of a cone and a plane is established by passing a series of horizontal cutting planes perpendicular to the axis of the cone. In Figure 27.14 the frontal and horizontal views of the cone are given along with the edge view of three theoretical unlimited planes that intersect the cone. The horizontal view and the true shape of each intersection are required. The following steps were used to solve the problem:

1. Pass a series of evenly spaced horizontal cutting planes through the cone, CP1 through CP12.

2. Each cutting plane projects as a circle in the horizontal view.

3. EV1 intersects cutting planes 3 through 12 in the frontal view. Project each intersection point to the

horizontal view. The intersection of EV1 and the cone forms a parabola.

4. The true shape of the parabola is seen in a view projected parallel to EV1. The centerline of the

parabola is drawn parallel to EV1 and the intersection points of the plane (EV1) and each cutting

plane are projected from the frontal view. Distances are transferred from the horizontal view, as is

dimension A.

5. Repeat steps 3 and 4 to establish the intersection of EV2 and EV3 with the cone. EV2 projects as a

line in the horizontal view and as a hyperbola in a true shape view (2). EV3 forms an ellipse in the

horizontal view and projects as a true ellipse in a true shape view (3)

27.5.2 Intersection of an Oblique Plane and a Cone (Cutting Plane Method)

The cutting plane method can be used to determine the intersection of a plane and a cone if the plane is oblique in its given views. A series of evenly spaced vertical cutting planes s passed through the vertex of the cone and the plane. The cutting planes intersect the cone and the plane as straight line elements (lines) that lie on the plane. Each element intersects its corresponding line along the line of intersection of the plane and the cone. The point at which an element intersects its corresponding line on the plane locates a point on the line of intersection. This intersection point lies on the plane and on the cone's surface.

In Figure 27.15 oblique plane K-L-M-N and the right cone are given and their intersection line is required. The following steps were used in the solution:

1. Pass a series of evenly spaced vertical cuffing planes through the cone's vertex [Fig. 27.15(a)].

Project the elements to the frontal view and label as shown.

2. Each element corresponds to a cutting plane that intersects the cone and the plane [Fig. 27.15(b)].

As an example, a cutting plane passed through the cone and intersecting the plane forms elements

0H-2H and 0H-10H, and also intersects the plane at points AH and BH. Points AH and BH form line AH-

BH, which lies on the plane and represents the intersection of the cutting plane and the given plane.

3. Line A-B is projected to the frontal view where it intersects element 0F-2F at piercing point A1. Each

line formed by the intersection of the cutting plane and the plane intersects two corresponding

elements on the cone.

4. The line of intersection is determined by connecting the piercing points with a smooth curve.

5. The piercing points are projected to the horizontal view to locate the line of intersection in that view.

6. Visibility is then determined for both views using inspection or the visibility check.

27.6 Spheres

A sphere can be defined as a geometric form bounded by a surface containing all possible points at a given distance from a given point. A sphere is generated by rotating a circle around an axis line that passes through the sphere's center. Spheres are

double-curved surfaces and contain no straight lines. Spheres are represented as circles equal to their diameter in all projections.

Spheres or portions of spheres are found in the design of a variety of industrial products, consumer goods, toys, buildings, and vessels.

A plane passed through the center of a sphere and at an angle to the adjacent projection plane creates an elliptical line of intersection [A and B in Fig. 27.16(a)]. This type of intersection is known as a great circle of a sphere. A plane passed parallel to the adjacent projection plane and not through its center cuts a small circle [C and D in Fig. 27.16(b)].

27.6.1 Intersection of a Plane and a Sphere

The intersection of a plane and a sphere results in a circular line of intersection. If the plane is inclined, the line of intersection appears as an ellipse (Fig. 27.17). The extreme piercing points and, therefore, the major and minor axes must first be found using the edge view or cutting plane method. The actual ellipse can be constructed by means of an ellipse template using the major and minor axes. Another method involves plotting a series of piercing points established by cutting planes in a view showing the plane as an edge. inclined

In Figure 27.17 the intersection of the sphere and plane is required. The following steps were used to solve the problem:

1. Pass a series of evenly spaced horizontal cutting planes through the sphere and project to the

horizontal view. Each CP cuts a small circle section.

2. Each CP intersects the edge view of the plane and locates two piercing points, which are projected to

the horizontal view to establish the line of intersection. Finally, visibility is determined

27.7 Intersection of Prisms

The intersection of two prisms can be determined by the edge view method. The piercing point of an edge line of one prism and a surface of the other prism can be established in a view where one of the prisms is an edge view. This type of problem can be reduced to finding the piercing point of a line and a plane. Where each edge line of a prism pierces a surface (plane) of the other prism a point (piercing point) on the line of intersection is established. The line of intersection includes only surface lines of intersection, not those that will be "inside" the prisms.

In Figure 27.18 two right prisms intersect at right angles. The horizontal view shows the edge view of the rectangular prism and the profile view shows the triangular prism as an edge view. The following steps were used in the solution:

1. The edges of the triangular horizontal prism pierce the vertical prism in the horizontal view at

points 1 through 6. Edge line A pierces the surface bounded by lines D and G at piercing point 1 and

at piercing point 2 on the surface bounded by lines D and E.

2. Project points 1 and 2 to the frontal view until they intersect line A.

3. Repeat this procedure to locate piercing points 3, 4, 5, and 6 in both views.

4. The edges of the vertical rectangular prism pierce the surfaces of the horizontal prism in the profile

view at points 7, 8, 9, and 10. Edge line G pierces the surface bounded by lines B and C at piercing

point 7.

5. Project point 7 to the frontal view until it intersects line G.

6. Repeat step 5 to locate piercing points 8, 9, and 10.

7. Determine visibility and connect the piercing points to form the line of intersection.

27.7.1 Intersection of Two Prisms (Edge View Method)

The line of intersection of two prisms is established by finding the piercing points of the edge lines of one prism with each surface of the other prism. This process is repeated using the lines of the second prism and is theoretically the intersection of individual lines and planes or the intersection of two planes. Each prism must be shown as an edge view. If only one prism is given as an edge view, an auxiliary view must be projected showing the other prism as an edge view.

In Figure 27.19 the horizontal and frontal views of the two prisms are given. The line of intersection is required. The following steps were used to solve the problem:

1. Draw an auxiliary view showing the triangular prism as an edge view. Each of the edge lines of the

triangular prism is a frontal line (true length in the frontal view). Therefore draw F/A perpendicular to

line 1 and project auxiliary view A.

2. In the horizontal view, edge line 1 pierces the surfaces bounded by lines A and D at point 1. The

surface bounded by line A and B is pierced by line 2 at point 2 and line 3 at point 3.

3. Project points 1, 2, and 3 to the frontal view to establish the endpoints of lines 1-1, 2-2, and 3-3.

4. In auxiliary view A corner line A intersects two of the surfaces of the triangular prism at points 4 and 5.

5. Project piercing points 4 and 5 to the frontal view until they intersect corner line A.

6. Visibility is determined by inspection of the profile and horizontal view. Connect the piercing points in

the proper sequence. In the frontal view intersection lines 3-2 and 2-4 are visible; all others are

hidden.

The intersection of prisms is shown on a CAD system in Figure 27.20.

The cutting plane method can also be used to solve for the intersection of two prisms. In Figure 27.21 the three-sided vertical prism is intersected at an angle by a four-sided prism. Most of the piercing points were solved for by finding the piercing points of the edge lines of the four-sided prism and the planes of the vertical prism [Fig. 27.21(1)]. VCP (a vertical cutting plane) is used to complete the problem by finding where line B pierces the plane formed by lines E and D [Fig. 27.21(2)].

You May Complete Exercises 27.5 Through 27.8 at This Time

27.8 Intersection of a Prism and a Pyramid

The intersection of a prism and a pyramid requires the projection of a view where the prism shows as an edge. In Figure 27.22(a), the right prism intersects the pyramid. After the edge view of the prism was projected (auxiliary view A) the intersection is solved for by locating the piercing points of the shapes. In this example, cuttings planes were introduced to solve for the line of intersection since the solution could not be derived by the use of piercing points excessively. Figure 27.22(b) shows a physical model of the project.

27.9 Intersection of Cylinders

The intersection of two cylinders is a common industrial problem in piping and vessel design and in duct design for HVAC. Two intersecting perpendicular right cylinders of the same diameter intersect as shown in Figure 27.23. The line of intersection can be determined by showing each cylinder as an edge view and passing a series of equally spaced cutting planes through both cylinders. Each cutting plane intersects a cylinder as an element on its surface. The intersection of related elements determines the line of intersection. Each intersection point is actually the piercing point of an element of one cylinder and the surface of the other cylinder.

In Figure 27.23, both cylinders are the same diameter and intersect one another at right angles. The resulting curved line of intersection appears as straight lines in the frontal view. Therefore, in this case the line of intersection could have been determined by simply drawing the straight lines from point 1 to point 4 to point 7.

To solve for the perpendicular intersection of two cylinders, regardless of their diameters, a series of elements is drawn on the surface of one cylinder by equally dividing the edge view of the vertical cylinder (Fig. 27.23). Each vertical cutting plane passes parallel to the cylinder's axis and cuts a straight-line element on both surfaces. Points 1 through 7 represent the intersection of related elements established by the intersection of a cutting plane and each cylinder. The profile view can also be used to divide the horizontal cylinder equally and establish vertical cutting planes as shown.

27.9.1 Intersection of Two Cylinders (Not at Right Angles)

To find the intersection of two cylinders not at right angles, an edge view of both cylinders is necessary. Project an edge view of the cylinder, if it does not appear as an edge in a given view. Pass a series of cutting planes; each cutting plane intersects both cylinders as elements on their surface. Related elements intersect along the line of intersection of the two cylinders. Accuracy increases proportionally to the number of cutting planes and therefore piercing points. Piercing points are connected by means of a smooth curve. In Figure 27.24 an industrial drawing of two pipes intersecting at 45° is given. The template development is also shown.

27.10 Intersection of a Cylinder and a Prism at an Angle

In Figure 27.25 the vertical right cylinder and the inclined prism are given in the frontal and horizontal views. A series of cutting planes is drawn through an end view of the prism (right section) and parallel to the axis of the cylinder. The following steps were used to solve the problem:

1. Draw F/A perpendicular to the true length lines of the prism in the frontal view. Project auxiliary

view A. The cylinder need not be shown.

2. Pass a series of evenly spaced vertical cutting planes through the right section of the prism in auxiliary

view A. Show the cutting planes in the horizontal view.

3. The edge lines of the prism intersect the cylinder in the horizontal view. Project piercing

points A, B, C, and D to the frontal view.

4. Project elements established on the prism in auxiliary view A and elements established on the cylinder

in the horizontal view to the frontal view. Note that each cutting plane cuts two elements on the prism

and one on the cylinder. Therefore, each cutting plane locates two points on the line of intersection.

5. Connect the intersection points in proper sequence after determining visibility.

In Figure 27.26 a series of vertical cutting planes are used to solve for the intersection of the right prism and the cylinder. The cutting planes are introduced vertically in the H and P views. The intersection of a cutting plane and the cylinder creates an element on the surface of the cylinder. The intersection of an element and the edge view of one prism’s plane determines one point of intersection.

27.11 Intersection of Cones and other Shapes

Conical shapes are used in the design of a wide variety of industrial products, structures, and commercial applications. In general, the right circular cone and the frustrum of a right circular cone are the most common. Oblique cones with circular bases are sometimes used as transition pieces and in ducting HVAC designs. In Figure 27.27 a number of conical and cylindrical intersections can be seen.

27.11.1 Intersection of a Cone and a Horizontal Cylinder

The intersection of a cone and a cylinder can be determined by passing a series of CPs through the cylinder's axis in a view where the cylinder appears as a right circular section. In Figure 27.28 the intersection of a cone and a cylinder is required. The following steps were used in the solution:

1. Project the profile view to show the right section of the cylinder.

2. Evenly divide the cylinder as shown. Each division corresponds to a horizontal cutting plane, CP1

through CP7. Extend the cutting planes to the frontal view.

3. The highest and lowest points of the intersection are established in the frontal view where CP1

intersects the cone at point 1 and CP7 at point 7. Project points 1 and 7 to the horizontal view.

4. Project the cutting planes to the horizontal view. Each CP appears as a circle element on the cone

and a straight-line element on the surface of the cylinder.

5. The intersection of related elements determines a point on the line of intersection. Locate the points

in both views.

6. Except for points 1 and 7, each common point is used to plot a line of intersection that is

symmetrical to the axis of the cylinder in the horizontal view.

7. Determine visibility and connect the points as a smooth curve representing the line of intersection.

In Figure 27.29 the intersection of the right cone and a vertical cylinder is provided. Here, a series of evenly spaced vertical cutting planes are introduced through the cone’s vertex. Each cutting plane cuts related elements on the surface of the cone and the cylinder. The intersection of related elements establish points of intersection. Figure 27.30(a) shows a similar intersection created on AutoCAD as a solid model. The top, front, right side, and pictorial views of the intersection are shown in Figure 27.30(b). This is a good example of one of the problems at the ed of the chapter (see Problem 27.1l).

27.11.2 Intersection of a Cone and a Cylinder at an Angle

A vertical cutting plane passed through the vertex of the cone and parallel to its axis intersects both the cone and cylinder as straight-line elements on their surfaces. A right section view of the cylinder is required to fix the position of the elements along its surface. In Figure 27.31 the intersection of a cone and a cylinder is required. The following steps were used to solve the problem:

1. Project auxiliary view A perpendicular to the cylinder. The cylinder appears as a right section.

2. Evenly divide one-half of the circumference of the cone's base in the horizontal view. Since the

intersection is symmetrical about the cylinder's axis, only the front divisions need be used as cutting

planes. Each division corresponds to a vertical CP passed through the vertex of the cone.

3. Each CP cuts a straight line element along the surface of the cone. Locate the CPs in each view by

projection of the elements of the cone.

4. The intersection of the CPs and the cylinder in auxiliary view A establish related elements along the

surface of the cylinder. Project the cylinder's elements to the frontal view.

5. The intersection of related elements in the frontal view determines points along the line of intersection.

CP1 locate points 1 and 6 at the extremes of the intersection line. CP2 locates points 2 and 5.

27.11.3 Intersection of a Cone and a Prism

The intersection of a cone and a prism can be established by passing a series of cutting planes through the shapes. When the prism is a vertical prism, cutting planes perpendicular to the cone's axis should be used (Fig. 27.32).

In Figure 27.33 the intersection of a prism and a right circular cone is required. The following steps were used to solve the problem:

1. Pass horizontal CP1 and CP2 through the upper and lower horizontal planes of the prism. Project

the CPs to the horizontal view where they appear as circle elements.

2. Since the upper and lower surfaces of the prism are horizontal planes, the line of intersection

coincides with the circle elements cut by the CPs.

3. When the prism's surfaces are not horizontal planes, vertical CPs passed through the axis of the cone

in the horizontal view are used. CPs 3, 4, 5, and 6 cut elements along the cone's surface.

Their intersection with the prism in the frontal view cuts two elements each on the prism.

4. Intersecting elements determine the line of intersection in the horizontal view.

27.12 Intersection of a Sphere and a Cylinder

By passing a series of cutting planes parallel to the axis of a cylinder and through a sphere, points along the line of intersection can be determined. A cutting plane drawn parallel to the axis of a cylinder will cut straight-line elements along its surface. Therefore, the intersection of a related circle and straight-line elements establishes points on the line of intersection. Each point represents a point common to both the sphere and the cylinder. Cutting planes are conveniently passed parallel to the axis of a cylinder where the cylinder appears as an edge (right section). A right section shows the cylinder's axis line as a point view.

In Figure 27.34 the frontal and horizontal view of a sphere, and the horizontal view of a sphere and of a horizontal cylinder are given. The line of intersection is required. The following steps were used in the solution:

1. Draw H/A perpendicular to the cylinder's axis and project auxiliary view A. The cylinder appears as a

right section with its axis line as a point view.

2. Pass a series of conveniently spaced horizontal cutting planes through the edge view of the cylinder

and the sphere in auxiliary view A. Show the cutting planes in the frontal view. Project the cutting

planes to the horizontal view, where they appear as circles on the sphere.

3. CP1 cuts a straight-line element along the upper surface of the cylinder and a circular element on the

surface of the sphere. The intersection of the sphere's circular element and the cylinder's straight-line

element in the horizontal view locates a point on the line of intersection, point 1.

4. CP2 and CP3 intersect the sphere as circular elements and cut two straight line elements each on the

surface of the cylinder.

5. Project all points to the frontal view to their corresponding cutting planes.

6. Determine visibility and connect the points in proper sequence to establish the line of intersection.

Since the cylinder goes through the sphere (pierces it), two curved lines of intersection result.

This chapter has provided many examples of simple to complex intersections of surfaces. The type and number of intersections found in industry is infinite, but the basic procedures and techniques found in this chapter can be applied to all intersecting forms.

You May Complete Exercises 27.9 Through 27.12 at This Time

27.13 Intersection Solutions Using CAD

Intersections of surfaces can be determined by using a number of different techniques. The basic primitives are combined automatically by the system, without the need to do descriptive geometry drawings. Both surface (Fig. 27.35) and solid modeling (Fig. 27.36) provide complete capabilities for intersection problems.

Piercing points and intersections of lines, planes, and solid shapes can be generated automatically with 3D CAD using commands such as CUT SURFACE, INTERSECT SURFACE, CUT PLANE (Computervision) and UNION (AutoCAD).

Figure 27.37 shows an example of a solid modeling system used to solve for the union of two solids (CADKEY). The figure displays the two solids together and separately. Figure 27.38 (CADKEY) shows an example of a complex shape and its intersection with a solid cylindrical shape. This type of modeling uses the power of the computer to merge the two solids automatically.

The intersection of two planes (Fig. 27.39) requires a minimum of two views when using the cutting plane method and three views with the edge view method. The CAD solution requires that a CUT PLANE (Computervision and Personal Designer) command be given and the two planes picked. The system automatically generates the intersection points. However, depending on the system, the line of intersection may need be put in with a command to draw a line. The system may also require that the operator give a HIDE command in order to show proper visibility.

The intersection of a plane and a pyramid is shown in Figure 27.40. The CUT PLANE command (Computervision and Personal designer) was used and correct visibility was established. The intersection of the plane and the cylinder (Fig. 27.41) required the addition of elements along the surface of the cylinder in the manual method. The curved line of intersection is generated automatically with the CUT PLANE command (Computervision and Personal Designer). Correct visibility was not established in this problem. Conic sections can also be automatically generated with a 3D CAD system as shown in Figure 27.42. The rotated view shows the intersections with crosshatching used to highlight the sections.

The intersection of a cone and an oblique plane is shown in Figure 27.43. The manual method required the introduction of multiple cutting planes forming lines on the plane and elements on the surface of the cone. The CAD solution required the entering of the CUT SURFACE command (Computervision and Personal Designer). The plane is identified by picking its edges and then selecting the cone. The system establishes the line of intersection (visibility is not determined).

27.13.1 Intersection Using CAD Solid Modeling

When completed manually, the intersection of two solids is one of the most difficult problems encountered in descriptive geometry. When using a solid modeling program, the same intersections are simple and easy to construct. The following examples were modeled on AutoCAD using solid modeling.

In Figures 27.44 through 27.48 a series of projects using AutoCAD solids is provided. These figures illustrate how to input the commands to create the solids and to solve for their intersection using a UNION command. The HIDE and SHADE commands complete the examples. The results of the shade commands are not shown. If you have an AutoCAD system, try each of the commands and plot the illustrations as required. These AutoCAD commands represent the latest release of the software.

Figure 27.44

Command: VPOINT

Rotate/ : 1, -1, 1

Command: PAN

Displacement: 0,0

Second point: 5,4

Command: ISOLINES

New value for Isolines : 10

Command: WEDGE

Center/ : Press Enter

Cube/Length/: 7,4,3

Command: COLOR

New object color : Blue

Command: CYLINDER

Elliptical/ : 3,2,0

Diameter/: 1

Center of other end/: 3

Command: UNION

Select objects: Pick the wedge and the cylinder

Command: ZOOM

All/ Center/Dynamic/Extents /Left/Previous /Vmax/Window/: AII

Command: HIDE

Command: SHADE (not shown)

Figure 27.45

Command: VPOINT

Rotate/ : 1,- 1,1

Command: PAN

Displacement: 0,0

Second point: 5,4

Command: ISOLINES

New value for Isolines : 10

Command: BOX

Center/ : Press Enter

Cube/Length/: 6,4,2

Command: COLOR

New object color : Blue

Command: CYLINDER

Elliptical/ : 2,2,0

Diameter/: .5

Center of other end/: 4

Command: CYLINDER

Elliptical/ : 4,2,0

Diameter/: .5

Center of other end/: 4

Command: SUBTRACT

Select solids and regions to subtract from...

Select objects: Pick the box

Select objects to subtract from them. . .

Select objects: Pick the first cylinder

Command: UNION

Select objects: Pick the box and the second cylinder

Command: ZOOM

All/Center/Dynamic/Extents/Left/Previous/Vmax/Window/: AII

Command: HIDE

Command: SHADE (not shown)

Figure 27.46

Command: VPOINT

Rotate/ : 1,-1, 1

Command: PAN

Displacement: 0,0

Second point: 5,4

Command: ISOLINES

New value for Isolines : 10

Command: CYLINDER

Elliptical/: 0,0,-5

Diameter/: 1

Center of other end/: 10

Command: COLOR

New object color : Blue

Command: UCS

Origin/ZAxis/3point/Object /View/X/Y/Z/Prev/Restore/Save/Del/?/: Y

Rotation angle about Y axis : 90

Command: CYLINDER

Baseplane/Elliptical/: 0,0,-5

Diameter/: .75

Center of other end/: 10

Command: UNION

Select objects: Pick the two cylinders

Command: ZOOM

All/ Center/Dynamic/Extents /Left/Previous /Vmax/Window/: AII

Select objects: Pick the object

Command: HIDE

Command: SHADE (not shown)

Figure 27.47

Command: VPOINT

Rotate/ : 1,-1,1

Command: PAN

Displacement: 0,0

Second point: 5,4

Command: ISOLINES

New value for Isolines : 10

Command: SPHERE

Center of sphere : Press Enter

Diameter/ of sphere: 2

Command: COLOR

New entity color : Blue

Command: UCS

Origin/ZAxis/3point/Object /View/ X/Y/ Z/Prev/Restore/Save/Del/?/: Y

Rotation angle about Y axis : 90

Command: CYLINDER

Elliptical/: 0,0,-5

Diameter/: .75

Center of other end/: 10

Command: UNION

Select objects: Pick the sphere and the cylinder

Command: ZOOM

All/ Center/Dynamic /Extents / Left/ Previous/Vmax/Window/: AII

Command: HIDE

Command: SHADE (not shown)

Figure 27.48

Command: VPOINT

Rotate/ : 1,-1,1

Command: PAN

Displacement: 0,0

Second point: 5,4

Command: ISOLINES

New value for Isolines : 10

Command: SPHERE

Center of sphere : Press Enter

Diameter/ of sphere: 2

Command: COLOR

New entity color : Blue

Command: CONE

Elliptical/ : 0,0,-5

Diameter/: 2

Apex/: 10

Command: UNION

Select objects: Pick the sphere and the cone

Command: ZOOM

All /Center/Dynamic/Extents/Left/Previous/Vmax/Window/: AII

Command: HIDE

Command: SHADE (not shown)

CHAPTER 27

INTERSECTIONS

QUIZ

True or False

1. A cutting plane can be introduced at any angle and in any view.

2. A cone is generated by a straight-line element passed through the axis and

at a specific distance from the vertex.

3. A piercing point and an intersection point are the same thing.

4. Most cylinders are cylinders of revolution.

5. The intersection of a plane and another shape can be established in a view where

the plane appears as an edge.

6. An isosceles triangle is established by passing a plane through a triangular prism.

7. A plane passed parallel to the adjacent projection plane and not through its

center cuts a small circle from a sphere.

8. The intersection of a sphere and a plane results in a circular line of intersection.

Fill in the Blanks

9. The cutting plane method needs only __________ adjacent ________ to solve

for the intersection.

10. The line of intersection between two surfaces is defined by a series

of ________ _________ representing the ________ of __________ .

11. A cylinder is a ________ ________ surface.

12. A sphere is a _______ ________ surface.

13. Passing a plane through a sphere's center results in a ___________ .

14. A right cone is generated by revolving a _________ about one of its legs.

15. An __________ is the result of a plane cutting all the elements of a cone.

16. A double curved surface contains no ________ _________ .

Answer the Following

17. Define the term conic section.

18. Describe the cutting plane method and the edge view method of solving

for intersections.

19. Name three specific engineering applications for intersecting shapes.

20. When a plane intersects a circular cylinder at an angle to the cylinder's axis,

the resulting intersection makes what type of shape?

21. Explain what is meant by common line or the line of intersection

22. What is a cylinder of revolution?

23. Name the five types of sections resulting from a plane intersecting a cone.

24. What is a sphere and how is it generated?

CHAPTER 27

INTERSECTIONS

EXERCISES

Exercises may be assigned as sketching, instrument, or digitizing CAD projects. Transfer the given information to an at" size sheet of .25 in. grid paper. Complete all views and solve for proper visibility, including centerlines, object lines, and hidden lines. Exercises that are not assigned by the instructor can be sketched in the text to provide practice and understanding for the preceding instructional material.

After Reading the Chapter Through Section 27.3.2 You May Complete the Following Exercises

Exercises 27.1(A) Through (C) Solve for the intersection of the two planes.

Exercise 27.2(A) Use the edge view method to solve for the intersection of the plane and the prism.

Exercise 27.2(B) Determine the intersection between the oblique plane and oblique prism.

Exercises 27.3(A) Through (C) Using the cutting plane method, determine the intersection between the oblique plane and right prism.

Exercise 27.4(A) Solve for the intersection of the pyramid and the plane by use of the edge view method.

Exercise 27.4(B) Determine the intersection of the oblique plane and pyramid using the cutting plane method.

After Reading the Chapter Through Section 27.7.1 You May Complete the Following Exercises

Exercise 27.5(A) Complete the two views of the intersection plane and cylinder.

Exercise 27.5(B) Solve for the intersection of the plane and the cone. Use the cutting plane method.

Exercise 27.6 The front view of the right cone is cut by three separate planes. Show the resulting true shape conic sections and the intersection lines in the H view.

Exercises 27.7(A) and (B) Solve for the intersection of the plane and sphere.

Exercise 27.7(C) Complete the views and determine the intersection of the two prisms.

Exercise 27.8(A) Using the edge view method, complete the views and solve for the intersection of the two prisms.

Exercise 27.8(B) Solve for the intersection of the pyramid and prism. Use the cutting plane method.

After Reading the Chapter Through Section 27.10 You May Complete the Following Exercises

Exercise 27.9 Complete the given views and solve for the intersection by means of an edge view.

Exercise 27.10(A) Solve for the intersection between the given cylinders.

Exercise 27.10(B) Determine the intersection between the prism and the cylinder.

Exercise 27.11 Complete the three views of the cone intersected by the cylinder.

Exercises 27.12(A) and (B) Complete the views of the intersecting shapes.

CHAPTER 27

INTERSECTIONS

PROBLEMS

Problems may be assigned as sketching, instrument, or CAD projects.

Problems 27.1(A) Through (L) Transfer the problem to another sheet. Most problems will fit on an "A" size drawing format. Complete the views of each intersection project. Add any view needed to complete the project. Use the edge view or the cutting plane method. Instructor may assign some projects for development problems after Chapter 27 is completed. Models of any of the problems can also be assigned.

CHAPTER 27

INTERSECTIONS

FIGURE LIST

Figure 27.1(a) Petrochemical Refinery (no courtesy required)

Figure 27.1(b) Complex Piping Substation

Figure 27.1(c) Pumping Station

Figure 27.2 Scale Model of Clean Room

(Courtesy Lockheed)

Figure 27.3 Turboprop Design

Figure 27.4 Tilt Stand

(Courtsey Lockheed)

Figure 27.5 Intersection of Two Planes Using the Edge View Method

Figure 27.6 Intersection of Two Oblique Planes Using the Edge View Method

Figure 27.7 Intersection of Two Planes Using the Cutting Plane Method

Figure 27.8 Intersection of a Plane and a Prism

Figure 27.9 Intersection of an Oblique Plane and Oblique Prism Using

the Edge View Method

Figure 27.10 Intersection of a Plane and Right Prism Using the Cutting Plane Method

Figure 27.11 Intersection of an Oblique Plane and Oblique Prism Using the

Cutting Plane Method

Figure 27.12 Intersection of an Oblique Plane Right Cylinder Using the

Cutting Plane Method

Figure 27.13 Intersection of an Oblique Prism and an Oblique Plane

Figure 27.14 Conic Sections

The intersection of a plane and a right cone forms one of

the following: 1) parabola, 2) hyperbola, 3) ellipse

Figure 27.15 Intersection of an Oblique Plane and a Right Cutting Plane Method

Figure 27.16 Great and Small Circles of a Sphere

Figure 27.17 Intersection of a Plane and a Sphere Using Cutting Planes

Figure 27.18 Intersection of Two Prisms

Figure 27.19 Intersection of Two Prisms Using the Edge View Method

Figure 27.20 Solid Intersection

Figure 27.21 Intersection of a Vertical Prism and an Inclined Prism

Figure 27.22(a) Intersection of a Pyramid and a Prism

Figure 27.22(b) Model of the Intersection of a Pyramid and a Prism

Figure 27.23 Intersection of Two Cylinders at 90(

Figure 27.24 4 inch OD to 4 inch Stub-in at 45(

Shown with Template Development

Figure 27.25 Intersection of a Cylinder and a Prism at an Angle

Figure 27.26 Intersection of a Right Prism and a Horizontal Cylinder

Figure 27.27 Electronic Testing of Top Hat and Probe

(Courtesy Lockheed)

Figure 27.28 Intersection of a Cone and Horizontal Cylinder

Figure 27.29 Intersection of a Cone and a Vertical Cylinder

Figure 27.30(a) Solid Intersection Shaded Model Using AutoCAD

Figure 27.30(b) Four Views of Solid Intersection Using AutoCAD

Figure 27.31 Intersection of a Cone and a Cylinder at an Angle

Figure 27.32 Intersection of a Cone and a Vertical Cylinder

Figure 27.33 Intersection of a Cone and Horizontal Prism

Figure 27.34 Intersection of a Sphere and a Horizontal Cylinder

Figure 27.35 3D Surface Model of Hair Dryer

Figure 27.36 Solid Model Created with AutoCAD

Figure 27.37 Solid Intersection

a) Solid Model of an intersection cylinder and block

b) Solid Model of a block with the cylinder removed,

thereby creating a hole.

c) Solid Model of cylinder with block removed

Figure 27.38 Solid Intersection of a Sculpted Surface and a Cylinder

Figure 27.39 CAD-Generated Solution for the Intersection of Two Planes

Figure 27.40 CAD-Generated Solution for the Intersection of a Plane and a Pyramid

Figure 27.41 CAD-Generated Intersection of a Plane and a Cylinder

Figure 27.42 CAD-Generated Conic Sections

Figure 27.43 CUT SURFACE Command Used to Solve for the Intersection

of a Plane and a Cone

Figure 27.44 Union of a Cylinder and Wedge Using AutoCAD

Figure 27.45 Union of Two Cylinder and a Box Using AutoCAD

Figure 27.46 Union of Two Cylinders Using AutoCAD

Figure 27.47 Union of a Cylinder and a Sphere Using AutoCAD

Figure 27.48 Union of a Cone and a Sphere Using AutoCAD

CHAPTER 27

INTERSECTIONS

ITEMS OF INTEREST

Camera Design

Use Items of Interest from TDD with corrections as shown.

Cameras are now developed and designed using a variety of modeling methods. The camera here is modeled using constructive solid geometry. Constructive solid geometry (CSG) modeling is a powerful technique that allows flexibility in both the way primitives are defined and the way they are combined. The relationships between the primitives are defined with Boolean operations. There are three types of Boolean operations: union ((), difference (-), and intersection (n). The camera design shows the use of union and difference operations can be used to create different forms. The critical area is the place where two objects overlap. This is where the differences between the Boolean operations are evident. The union operation is essentially additive, with the two primitives being combined. However, in the final form, the volume where the two primitives overlap is only represented once. Otherwise there would be twice as much material in the area of overlap, which is not possible in a real object. With a difference operation, the area of overlap is not represented in all. The final form resembles one of the original primitives with the area of overlap removed. With the intersection operation, only the area of overlap remains; the rest of the primitive volumes is removed.

In Figure 7.20, Boolean operations are shown in their mathematical form. The union (() operation, like the mathematical operation of addition, is not sensitive to the order of the primitive operands (i.e., 11 + 4 and 4 + 11 both equal 15). On the other hand, the difference (-) operation is sensitive to order. To extend the analogy, 11 - 4 equals 7, but 4 -11 equals -7. For a Boolean difference operation is that the overlapping volume is removed from the primitive listed first in the operation.

With Boolean operations, it is possible to have a form that has no volume (a null object, diam.) if the second primitive of the difference operation completely encompasses the first primitive, the result will be a null object, since negative geometry cannot be represented in the model.

Primitives that adjoin but do not overlap are also a special case. Performing a union operation on such primitives, will simply fuse them together. A difference operation will leave the first primitive operand unchanged. An intersection operation will result in a null object, since such an operation only shows the volume of overlap and there is no overlap for the adjoining primitives.

The final form of a model can be developed in several ways. As with pure primitive instancing, you can begin by defining a number of primitive forms. The primitives can then be located in space such that they are overlapping or adjoining. Boolean operation can then be applied to create the resulting form. The original primitives may be retained in addition to the new form, or they may be replaced by the new form. More primitives can be created and used to modify the form, until the final desired shape is reached. The camera sequence shows how the union and difference operation result in a solid model of the camera.

As with pure primitive instancing, the person doing the modeling must have a clear idea of what the final form will look like, and must develop a strategy for the sequence of operations needed to create that form. The use of sweeping operations to create primitives can lend even more flexibility in modeling.

Captions

Solid Model of a Camera

Constructive Solid Geometry (CGS) Modeling of a Camera

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