The Right Angle Join is the flat pattern (development) of a thin walled two piece 90° elbow: two straight cylinders of the same diameter joined by a single 45° mitre. You enter the diameter and the length of each leg; the shape cuts the two flat blanks that are rolled or brake-formed into the legs and welded together at the mitre, and can mark the fold lines on them. The 3D view shows the formed elbow.
It appears in the shapes library under Thin Walled Developments. For an elbow made of more than two pieces, or turning through an angle other than 90°, use Arbitrary Lobster, which is built the same way but also has Radius, Parts, Angle and Start Angle properties.
Right Angle Join in PrimeShape: the property page (left) and the shape as a wireframe with its dimensions (right).
How the shape is built
In 3D the base leg stands upright and the top leg turns through 90° to run horizontally; the two legs meet on a 45° mitre plane. The bend centre (the line about which the elbow turns) is a fixed 1 mm inside the inner wall of both legs; this inside radius is not on the property page. Base Height and Top Length are measured from the bend centre, so:
•the base leg is Base Height + 1 mm long on the inside of the elbow (the throat) and Base Height + 1 mm + Diameter long on the outside (the heel)
•the top leg is Top Length + 1 mm long on the throat and Top Length + 1 mm + Diameter long on the heel
The round wall of each leg is approximated by Dev. Segs flat facets whose corners lie on a circle of the given Diameter. Each leg is unrolled into its own blank, one circumference wide along X, with the fold lines running along Y. The insert point is the top left corner of the base leg blank: the straight top edge of the blank is the open end of the base leg (the bottom of the upright leg in 3D), the blank runs to the right (+X) and downward (–Y), and its lower edge is the mitre curve. The top leg blank is placed below it, separated by Development Spacing; its mitre edge faces the base blank and its straight lower edge is the open end of the top leg.
The seam (the joint where a blank closes) of the base leg is on the throat, so the two side edges of the base blank are its shortest lines and the mitre curve is deepest in the middle. Where the seam of the top leg goes depends on Stacked (see below). The fold lines between the facets (Dev. Segs – 1 per blank) are added as marking lines when Show Bends is on.
Stacked
With Stacked True the seam of the top leg is turned through 180° to the heel. Its mitre edge is then the same curve as the mitre edge of the base blank, and the top blank is placed directly below the base blank with the two mitre curves nested one inside the other, Development Spacing apart. This saves plate, but the two seams finish on opposite sides of the elbow (base leg on the throat, top leg on the heel). Stacked also rounds an odd Dev. Segs up to the next even number, and the property page shows the new value.
With Stacked False both seams are on the throat. The top blank is placed so that its highest point is Development Spacing below the lowest point of the base blank, so the blanks do not nest.
Properties
Property |
Description |
Default |
Top Length |
Length of the horizontal (top) leg, from the bend centre to its open end, along the leg (mm or inch). The throat line of the top blank is Top Length + 1 mm long. |
100 mm (4 in) |
Base Height |
Height of the upright (base) leg, from its open end up to the bend centre (mm or inch). The throat line of the base blank is Base Height + 1 mm long. |
50 mm (2 in) |
Diameter |
Diameter of both legs (mm or inch). The facet corners and fold lines lie on this diameter. The shape has no material thickness setting, so enter the diameter at which the blanks should be developed – normally the mean (neutral axis) diameter of the wall. The heel of each leg is Diameter longer than its throat. |
200 mm (8 in) |
Development Spacing |
Gap between the base blank and the top blank (mm or inch). With Stacked True it is the gap between the nested mitre edges; with Stacked False it is the gap from the lowest point of the base blank to the highest point of the top blank. |
5 mm (about 0.2 in) |
Stacked |
True moves the seam of the top leg to the heel and nests the two blanks on their mitre edges; False keeps both seams on the throat and lays the blanks out separately. See Stacked above. |
True |
Dev. Segs |
Number of flat facets each leg is divided into. Each facet is one strip of the blank, with one fold line between each pair of facets. More segments give a rounder elbow. Each leg has Dev. Segs minus 1 fold lines. The least allowed is 3. When Stacked is True an odd value is rounded up to the next even number. |
24 |
Show Bends |
True adds the fold lines to both blanks as marking lines, so they are processed with the marking tool. Alternate lines are reversed so the marking runs back and forth across the blank. False cuts the outlines only. |
True |
Bend Length (0 for Full) |
Length of the fold-line marks (mm or inch). A value above 0 replaces each fold line with two short marks of this length, one at each edge of the blank. A fold line shorter than 2.1 × Bend Length is marked full length. 0 marks every fold line full length. Only used when Show Bends is True. Cannot be negative. |
12.5 mm (0.5 in) |
The dimensions shown on the 3D view are Base Height, Top Length and Diameter.
Notes
•The bend angle is fixed at 90°, the elbow is always two pieces, and the 1 mm inside radius cannot be changed on this shape.
•Top Length, Base Height, Diameter and Development Spacing have no limits on the property page; enter values greater than 0. Dev. Segs cannot be set below 3 and Bend Length cannot be negative.
•If the blanks cannot be built from the values entered, the property page shows Warning: Cannot build shape from these parameters and the 3D view is cleared. Correct the values to rebuild it.
•The defaults for Top Length, Base Height and Diameter are in millimetres in metric and in inches (4 in, 2 in, 8 in) in imperial. Development Spacing defaults to 5 mm (about 0.2 in) and Bend Length to 12.5 mm (0.5 in) in imperial.
•The shape has no aliases (no former names).
The Right Angle Join also has the Transform properties (Base X, Base Y, Rotation, Scale, Mirroring X), listed after the shape's own properties. They place the flat blanks. As a 3D development shape it has no Polar Array properties; those apply to 2D shapes only.