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The Circle To Circle Transition is the flat pattern (development) of a thin sheet-metal piece that joins two circles of different size. The top circle can be offset sideways from the bottom circle, and either end can be tilted, so the same shape covers concentric reducers, eccentric (offset) reducers and transitions between pipes that are not parallel. You enter the 3D part; the shape unrolls it into a 2D profile that is cut from flat plate and rolled or press-braked to shape, with optional bend lines marked on it.

It appears in the shapes library under Thin Walled Developments.

How the part is defined

The 3D part is set up in its own X, Y, Z axes:

•The bottom circle is centred on X 0, Y 0, Z 0.

•The top circle is centred on X = Top Offset X, Y = Top Offset Y, Z = Center H.

•Each end lies flat (in the XY plane) unless it is tilted. Angle Y sets how far that end is tilted; Angle Z sets the direction, seen from above and measured from the X axis, in which it slopes. A tilted end is still a true circle of the entered diameter in its own plane.

The side wall between the two circles is divided into Dev. Segs flat strips. Each strip joins two neighbouring points on the bottom circle to the matching two points on the top circle. The strips are then laid out flat, one after another, to form the pattern. The top and bottom edges of the pattern are therefore made of straight lines, one per strip, not arcs; more segments give a smoother edge.

The shape has no plate thickness property. The pattern is built exactly on the diameters entered, so enter the diameters on which you want the development taken (for example the mean diameter of the finished part).

Insert point and the flat pattern

The pattern is one closed profile: a seam line, the top (smaller) edge, the second seam line and the bottom (larger) edge. The seam is where the rolled part is joined. The first seam line is laid along the X axis with its top end on the insert point and its bottom end at X equal to the seam length; the rest of the pattern unrolls to one side of it. Start Angle sets where round the part the seam is.

When Show Bends is on, the fold line between each pair of neighbouring strips is added as a marking line (one fewer line than Dev. Segs, as the last fold is the seam). These lines show where to roll or brake the plate.

Properties

Dev. Segs, Show Bends and Bend Length (0 for Full) are common to the thin walled development shapes and are listed after the shape's own properties. In the 3D view the shape shows dimensions for Center H, Bottom D, Top D, Top Offset X, Top Offset Y and the four end angles.

Notes

•The shape checks only the limits in the table (Top D and Bottom D at least 1, Bend Length not negative, Dev. Segs at least 3). If the part cannot be built from the values entered, the property page shows Warning: Cannot build shape from these parameters and no 3D part is drawn.

•Entering a Top D larger than Bottom D swaps the two values; the property page then shows the swapped values.

•Each circle is approximated by Dev. Segs straight lines, so the ends and the top and bottom edges of the pattern are polygons. Raise Dev. Segs for a closer approximation; with Show Bends on, it also adds bend lines.

•The defaults are in millimetres in metric and in inches in imperial. The Bend Length default is 12.5 mm in metric and 0.5 in in imperial.

•The shape has no aliases (no former names).

This shape also has the Transform properties (Base X, Base Y, Rotation, Scale, Mirroring X), listed after the shape's own properties; they place the flat pattern in the drawing. It has no Polar Array properties – the polar array is available on 2D shapes only.