Cylinder with Rectangular Hole flat pattern
What it is
The shell with the rectangular tap's hole already marked — the mate of the rectangular tap, and the half that carries the number people get wrong. The hole IS a rectangle, which is what fools everyone; but the side that runs across the shell does not measure y.
Where it is used
Headers receiving rectangular ducts, shells for intake mouths, cyclone bodies with a rectangular inlet, any pipe that has to take a rectangular collar.
Measurements the calculation needs
- D2 Outside diameter of the shell
- H Length of the shell
- X Side of the collar along the axis
- Y Width of the collar, across the axis
- THK Plate thickness
Calculate with your own measurements
No account needed: enter the measurements in millimetres or inches and get the figures and the drawing. The scaled PDF template, the DXF for the cutting table and the 3D model take a free account.
Diameters and sides are outside measurements. The flat pattern already allows for the plate thickness, working on the mean line.
Inches or millimetres? mm inches
Worked example
The values the form comes pre-filled with, run through the tool itself:
| Outside diameter of the shell | 500 mm |
|---|---|
| Length of the shell | 700 mm |
| Side of the collar along the axis | 300 mm |
| Width of the collar, across the axis | 250 mm |
| Plate thickness | 3 mm |
| The flat pattern fits a plate of | 1561 × 700 mm |
Result of the example
| Plate | 1561 × 700 mm |
|---|---|
| Area and weight | 1.01 m² · ≈ 23.9 kg in 3 mm steel |
Ordinate table
| # | Position on the plate | Element height |
|---|---|---|
| 1 | 0 mm | 700 mm |
| 2 | 650.6 mm | 300 mm |
| 3 | 910.8 mm | 300 mm |
| 4 | 1,561.4 mm | 700 mm |
Frequently asked questions
- Why is the hole a rectangle at all?
- Because the collar's walls meet the cylinder along curves that unroll straight. The two perpendicular to the axis meet it along circles, which become lines of constant position along the pipe; the two parallel to the axis meet it along straight lines, which become lines of constant position around it. Straight on all four sides.
- Then why isn't it x by y?
- Because the sheet stretches when it unrolls. The side across measures the arc that y occupies: 2·Rn·asin(y/d2). On a 500 shell with a 250 tap it comes out 260.2. The wider the tap relative to the pipe, the worse — at a tap half the pipe's diameter the stretch passes 5%, and near the limit it passes 50%.
- What is the limit on the width?
- Half a turn. At y equal to the shell's mid-line diameter the hole opens exactly half the circumference and there is no shell left either side of it. The calculation refuses past that.
- Does it match the rectangular tap?
- It does, and it is its mate. Enter the same pipe and the same collar section in both parts and you have both patterns for the job.
You can work out the figures right here, with no account. PDF, DXF, 3D and history take an account — free, with unlimited calculations.