# Development of Transition Pieces

### From DT Online

##### Description

**Transition Pieces** are usually made to connect two different shaped objects *(e.g. round pipes to square pipes)* as often found in **Ducting** for **Air Conditioning** or **Dust** and **Fume Extraction** systems. The **Development** is constructed by assuming the surface to be made from a series of triangular surfaces laid side-by-side. This technique is known commonly as **Triangulation** and more specifically as **Trilateration**.
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##### Construction for a Square to Round Transition Piece

Consider the example of a **Square to Round Transition Piece** with both **Axes** directly in line with each other.

- Draw
**Plan**and**Elevation**of the required**Transition Piece**, - Divide the circle into, say, 12 equal points
*(Note : in this case, the distances in*.**Plan View**around the circle between these points; and the lengths of the sides of the square are all**True Views**because neither the circle nor the square are tilted in any way - i.e they both lie in the horizontal plane) - Join the corners of the square to the relevant points around the circle
*(Note : none of these are*,**True Views**because they are angled either away from or towards you) - Number all points carefully,
- Use
**Dividers**to transfer the lengths of the joining lines on to a horizontal line as shown*(Note : in this case there are only two lines different in length)*, - Using the
**Transition Piece**elevation as height and the joining line lengths in**Plan**as base, draw the hypotenuse to find**True Lengths**, - Work around the
**Plan View**and use**True Lengths**to construct triangles as follows:- Draw a line to the length of side
**A-D** - Set
**Compasses**to the**True Lengths**of**A-9**and**D-9**and strike arcs from each end of**A-D**to create the**Isosceles Triangle****A-D-9**, - Similarly strike arcs equal to
**True Length****D-10**and circle division**9-10**to find point**10**.

- Draw a line to the length of side
- Repeat the process, paying careful attention to the point numbering, to construct the full
**Development**.

##### General Method of Construction for Transition Pieces

A similar procedure can be used to determine the **Developments** for other **Transition Pieces** *(e.g. Rectangular to Round, Octagon or Hexagon)*; for those where the two main axes are offset; and for situations where one pipe is set at an angle to the other.

- Draw
**Plan**and**Elevation**of the required**Transition Piece** - Identify convenient points around the perimeter of each shape to be joined
*(e.g. corners of polygons or equidistant points plotted around the circumference of a circle)* - Note which lines are perpendicular to the viewer
*(and therefore*and which are not**True Views**with**True Lengths**)*(i.e. because they are sloping away from you or towards you)*. - If necessary
*(e.g. if the axis one pipe is set at an angle to the other)*, construct an**Auxiliary View**to establish**True Lengths**around the perimeters of both shapes to be joined. - Carefully number all lines joining the two shapes together and note any equalities to avoid unnecessary work later.
- Proceed as for the
**Square to Round**example above to find**True Lengths**of lines joining the two shapes together*(i.e. plot their*.**Lengths in Plan**against their**Heights in Elevation**) - Use the
**True Lengths**to plot by**Triangulation**all points on the required**Development**.