Transition development
One opening becomes another: square to round, round to oval, oval to rectangle, rectangular reducer, pyramid frustum, angular boot and discharge chute. Almost all are solved by triangulation, with the true length of every line.
Square to Round
Four flat corner triangles alternating with four conical sectors that carry the curve. Only triangulation solves it — there is no direct formula.
Inclined Square to Round
Square to round with the circular mouth tilted over the centre of the base. Symmetric about the line of steepest tilt, so half the pattern is mirrored.
Rectangular Transition
The pyramid frustum: a reducer between two rectangular mouths. Every face is a flat trapezoid, so its pattern is the face itself — no approximation.
Eccentric Rectangle to Round
Rectangle to round with the round mouth off centre. Every corner has its own true lengths, so the pattern has to be walked right around — no mirroring.
Discharge Chute
A rectangular hopper with its outlet tilted and off centre — the spout the material drops through. The faces are skew, so the pattern is triangulated.
Round to Oval
Round on top, flat oval below — the duct that has to get through a shallow void. The corners are arcs, so a triangulated strip runs to each one.
Angular Boot, Rectangle to Round
A rectangular mouth below and a round pipe leaving sideways. Its round mouth is not a circle — it is the angled cut of the pipe, so it is an ellipse.
Obround to Rectangle
The other end of the round-to-oval job: the flattened duct gets through the low gap, then has to meet the rectangular frame of a filter or a fan.
Regular Pyramid Frustum
Two coaxial regular polygons and s identical flat facets — the part behind polygonal chimney caps, hexagonal duct and cyclone baskets.
Oval to Oval Reducer
The middle piece the flat-oval run was missing: it steps the oval down without taking it out of oval. Concentric or flush-face, one number apart.
Which transition to use
- A rectangular or square opening becoming a round one, on the same axis: Square to Round. The transition of duct and hopper work.
- The two openings offset: Eccentric Rectangle to Round; the round opening tilted: Inclined Square to Round.
- Rectangle to a smaller rectangle, the four-sided hopper: Rectangular Transition. With more sides, Regular Pyramid Frustum.
- A hopper with one vertical face and the others sloping, the chute: Discharge Chute.
- Round duct becoming oval, or oval becoming rectangular: Round to Oval, Obround to Rectangle and Oval to Oval Reducer.
- A rectangular outlet at an angle to the round opening, the floor register: Angular Boot.
What they all share
Nearly every transition is solved by triangulation: the surface is divided into triangles between points on the two openings, the true length of each side is found with Pythagoras in three dimensions, and the plate is built triangle by triangle from a seam. The flat faces of a square to round are true triangles; the curved parts, fans of lines.
The dimensions are the two openings (sides or diameters), the height, the offset where there is one, and the thickness. The result comes with the true length of every line for marking out with a compass, the PDF template at 1:1, the DXF and the 3D view.
Frequently asked questions
- How do I develop a square to round?
- By triangulation: the round opening is divided into points, each point is joined to the corners of the square opening, and the true length of each line is √(projection² + height²). The plate is built with a compass, line by line, from the seam. The square to round guide shows the calculation and the layout.
- Where should the seam go on a transition?
- In the middle of a flat face, where the plate does not bend, or on a corner, where the bend hides the weld. Each transition page shows the opened plate from the seam and the 3D drawing to check it.
- One piece or two halves?
- It depends on the plate size and the rolls. A large part comes out as two symmetrical halves with two seams; the half-part template is the same layout cut on the axis.