A rectangular chute bend drawn from eleven sizes: cheeks, wrappers, flanges and a script that checks them
- Problem
- A rectangular chute that turns a corner is made of two side walls (cheeks), a heel wrapper and a throat wrapper folded at each joint, and two end flanges; every new size means redrawing all of them so they still meet.
- What was built
- A generator that runs in the browser: type eleven sizes on the drawing, and a seven-sheet set (PDF and DXF) and four cut DXFs are redrawn from one geometry, with a manifest and a verifier in the ZIP.
- Result
- The sample cut files pass 26 checks by an ezdxf script written separately from the drawing code; tests run it on six bends from a 30° mitre to a 180° return, in millimetres and inches.
Problem
Bulk material changes direction through chutes, and a rectangular chute bend is usually built as a segmented bend: two flat side walls (cheeks), a heel wrapper on the outside of the turn and a throat wrapper on the inside, each folded at the joints, with a flange on each end. The parts only fit if the cheek's edges, the wrapper fold positions and the flange opening all come from the same numbers.
Drawing it by hand takes time, and changing the width, the radius or the number of pieces means redrawing every part, with the usual risk that a wrapper no longer matches its cheek.
Constraints
- Runs in the visitor's browser. The sizes are never sent to a server; the ZIP is built on the visitor's computer.
- The PDF and the DXF must be the same sheets, not two drawings that happen to look alike.
- Millimetres or inches; inch sheets in fractions to 1/16, plate thicknesses in decimal inches; cut files in the unit chosen.
- Geometry and fabrication only. Plate thickness, welds and bolts are not sized for load, wear or flow; the notes say so, and the title block leaves space for the reviewing engineer's seal.
- Sizes that cannot be built are refused in plain words rather than drawn: a radius so tight that the cheek's inside edge folds back on itself, a flange land too narrow for its holes, a joint turning 90° or more.
How the logic works
The eleven sizes are the inside width and depth, the centreline radius, the turn, the number of pieces, the straight on each end, the plate thickness, and the flange land, thickness, hole diameter and largest bolt spacing. With n pieces the bend has n − 1 joints, each turning the total angle divided by n − 1; along the centreline each end piece is half a middle piece, plus the straight leg.
The cheek is the flat outline of that bend, standing proud of the wrappers by one plate thickness so the outside fillet has a ledge. The wrappers are strips as long as the heel and throat edges measured at the wrappers' mid-thickness, with a fold line at each joint. The flange opening clears the chute's outside by 1 mm a side, and its holes are spaced equally on each side, no wider than the largest spacing set.
Each sheet is one list of lines, arcs, text and tables in sheet millimetres. Three writers turn that list into an SVG for the screen, a PDF and a DXF R12, so the preview, the PDF and the CAD file are made from the same data.
System
| Sheet | Content |
|---|---|
| 1 | General arrangement |
| 2 | General notes |
| 3 | C1 cheek |
| 4 | H1, T1 wrappers — developed views and forming |
| 5 | E1 end flange |
| 6 | Welding details |
| 7 | Assembly |
The download is a ZIP: the drawing set as PDF and DXF, four cut DXFs named by drawing number, a manifest with the inputs and the derived sizes, the verifier and a README. The sheet editor, writers and title block are shared with the feed hopper drawing package.
Validation
- Independent check of the cut files. A Python script using ezdxf, written apart from the drawing code, reads the four cut DXFs and checks each against the geometry: equal turns at every joint, the piece lengths of the heel and throat edges, both legs measured from the intersection point, wrapper widths and fold positions, the flange opening, land and hole spacing, and the area and mass of each part against the bill of material in manifest.json (it reads the cut files, not the sheets). The sample passes all 26 checks (output).
- Six bends. Tests run the script on six bends (a 30° mitre without straights, 45° in 3 pieces, 60° in thick plate, 135° on a tight radius, a 180° return in 9 pieces, and the sample), with the cut files in millimetres and again in inches, and write all seven sheets of each to PDF and DXF.
- The sample is real output. A test fails if the sample files below differ by one byte from what the generator makes today.
Result
A drawing set for a new chute bend from the sizes typed in, with cut files checked against the geometry and the bill of material by a script anyone can run. The set still goes through the shop's own checking and the engineer's review. The generator is free to use on this site: open the chute bend drawing package.
Responsibility
The set is geometry and fabrication information. It does not size plate, welds, bolts, liners or supports, and it does not consider the material carried, its flow or wear. It needs review by a licensed professional engineer for the intended use before anything is built; the notes on sheet 2 say this on every set.
Technology
TypeScript · one sheet display list → SVG, PDF and DXF R12 writers · Python + ezdxf (independent check) · Vitest · Playwright