The Shifted Rect To Rect Transition is the flat pattern (development) of a transition piece that joins a rectangular opening at the bottom to a smaller or larger rectangular opening at the top. The top rectangle is horizontal and parallel to the base, and its centre can be moved off the centre of the base in X and Y. Cut the pattern from thin plate and fold it along the bend lines to make offset duct transitions, hoppers and chutes between two rectangular openings.
It appears in the shapes library under Thin Walled Developments. The shape is defined in 3D; the 3D view shows the folded part, and the part that is cut is the 2D flat pattern built from it. For a top rectangle centred over the base use the Right Rect To Rect Transition. A tilted top is not available: the Arbitrary Rect To Rect Transition is disabled and is not in the library.
Shifted Rect To Rect Transition in PrimeShape: the property page (left) and the shape as a wireframe with its dimensions (right).
How the part is defined
The base rectangle lies in the XY plane at Z 0, with one corner on the insert point (the origin). Base Width runs along +X and Base Height along +Y. The top rectangle (Top Width along X, Top Height along Y) lies flat at Z = Center H above the base. With Top Offset X and Top Offset Y at 0 its centre is directly over the centre of the base. The offsets move the centre of the top rectangle from there along X and Y; negative values move it the other way. The sides of the two rectangles stay parallel because the top is never rotated: the tilt values inherited from the base transition class are not on this shape's property page and stay at 0.
The surface is five flat panels. One panel joins each of the three sides of the base at X = 0, Y = 0 and Y = Base Height to the matching side of the top. The side at X = Base Width is two planar panels, split at the middle of the base side and the middle of the top side, so the pattern has a seam there.
Insert point and the flat pattern
The five panels are unrolled one after another into a single flat outline, which is drawn as one closed path. Its two ends are the two halves of the seam, and the path runs: seam, developed top edge, seam, developed base edge. The first seam is laid along the X axis with its top end on the insert point (0, 0) and its base end on +X, at a distance equal to the seam length. The pattern therefore builds from the insert point towards +X, with the top edge on one side of the seam line and the base edge on the other.
Bend lines
With Show Bends on, a bend line is added on each of the four corner lines, where two faces meet. They are marking entities, not cuts. Alternate bend lines are drawn in the reverse direction. If Bend Length is more than 0, each bend line is shortened to two marks of that length, one at each end, instead of a full line across the plate. A bend line shorter than 2.1 times Bend Length is left at full length.
Properties
The property page lists the shape's own properties first, then the development properties, then the Transform group.
Property |
Description |
Default |
Top Width |
Size of the top rectangle along X. Length units, minimum 1. |
50 mm (2 in) |
Top Height |
Size of the top rectangle along Y. Length units, minimum 1. |
100 mm (4 in) |
Base Width |
Size of the base rectangle along X. Length units, minimum 1. |
100 mm (4 in) |
Base Height |
Size of the base rectangle along Y. Length units, minimum 1. The seam is at the middle of one of the sides of this length. |
200 mm (8 in) |
Center H |
Vertical distance from the base to the top rectangle, along Z (the height of the part, not a slant length). Length units. The property page sets no minimum and the code does not check the value. |
75 mm (3 in) |
Top Offset X |
Distance along X from the centre of the base to the centre of the top rectangle. Positive moves the top towards +X, negative towards -X. Length units. No limit is set by the base size. The range is symmetrical about zero and is limited only by the edit control maximum. |
0 |
Top Offset Y |
Distance along Y from the centre of the base to the centre of the top rectangle. Positive moves the top towards +Y, negative towards -Y. Length units. No limit is set by the base size. The range is symmetrical about zero and is limited only by the edit control maximum. |
0 |
Dev. Segs |
Shared by all Thin Walled Developments. This shape is made only of flat faces, so the value is not used and changing it does not change the pattern. Whole number, minimum 3. |
24 |
Show Bends |
On: the four corner bend lines are added to the pattern as marking. Off: the pattern is the outline only. |
On |
Bend Length (0 for Full) |
Length of the bend marks at each end of a bend line. 0 marks the full bend line from edge to edge. Length units, 0 or more. Used only when Show Bends is on. |
12.5 mm (0.5 in) |
The dimensions drawn on the 3D view are Center H, Base Width, Base Height, Top Width, Top Height, Top Offset X and Top Offset Y.
Notes and limits
•The pattern is built on the surface defined by the sizes entered; there is no plate thickness or neutral-axis allowance. Enter the sizes you want the pattern laid out on (for example mean sizes for a part made from thick plate).
•The offsets are not limited by the base size: the top rectangle can be moved so that it overhangs the base, which gives faces that lean outwards.
•If the build fails for the values entered, the 3D view is cleared and the property page shows Warning: Cannot build shape from these parameters. The code catches any error during the build and does not list which combinations fail, so change the values until the warning goes away.
This shape also has the Transform properties (Base X, Base Y, Rotation, Scale, Mirroring X), listed after the shape's own and development properties. It is a 3D shape, so it has no Polar Array properties and the Shape-Polar-Array topic does not apply to it.