DEVELOPMENT OF TRANSITION PIECES

Transition pieces are usually made to connect two different forms, such as round pipes to square pipes. These transition pieces will usually fit the definition of a nondevelopable surface that must be developed by approximation. This is done by assuming the surface to be made from a series of triangular surfaces laid side-by-side to form the development. This form of development is known as triangulation (fig. 8-17).

Square to Round

The transition piece shown in figure 8-18 is used to connect round and square pipes. It can be seen from both the development and the pictorial drawings that the transition piece is made of four isosceles triangles, whose bases connect with the square duct, and four parts of an oblique cone having the circle as the base and the corners of the square pipe as the vertices. To make the development, a true-length diagram is drawn first. When the true length of line IA is known, the four equal isosceles triangles can be developed After the triangle G-2-3 has been developed, the partial developments of the oblique cone are added until points D and K have been located Next the isosceles triangles D-1-2 and K-3-4 are added, then the partial cones, and, last, half of the isosceles triangle is placed at each side of the development.

Rectangular to Round

The transition piece shown in figure 8-19 is constructed in the same manner as the one previously developed except that all the elements are of different lengths. To avoid confusion, four true-length diagrams are drawn and the true-length lines are clearly labeled.

Connecting Two Circular Pipes

The following paragraphs discuss the developments used to connect two circular pipes with parallel and oblique joints.

PARALLEL JOINTS.-The development of the transition piece shown in figure 8-20 connecting two circular pipes is similar to the development of an oblique cone except that the cone is truncated The apex of the cone, 0, is located by drawing the two given pipe diameters in their proper position and extending the radial lines 1-11 and 7-71 to intersect at point 0. Fit the development is made to represent the complete development of the cone, and then the top portion is removed. Radius settings for distances 0-21 and 0-31 on the development are taken from the true-length diagram.

Figure 8-18.-Development of a transition piece              square to round.

Figure 8-19.-Development of an offset transition piece- rectangular to round.

Figure 8-20.-Transition piece connecting two circular pipes-parallel joints

OBLIQUE JOINTS.-When the joints between the pipe and transition piece are not perpendicular to the pipe axis (fig. 8-21), then a transition piece should be developed. Since the top and bottom of the transition piece will be elliptical, a partial auxiliary view is required to find the true length of the chords between the end points of the elements. The development is then constructed in the same way as the development used to connect two circular pipes with parallel joints.

Figure 8-21.-Transition piece connecting two circular pipes-oblique joints.

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