Chinese Hat flat pattern
What it is
The conical cap is a full cone with no smaller opening: a disc with a wedge removed, closed into a cone. It is a cover, so it is almost always made in thin plate. The development is a disc sector whose angle depends only on the diameter and the height.
Where it is used
Chimney and vent caps, rain covers on vertical ducting, conical silo tops.
Measurements the calculation needs
- H Height
- D Diameter
- THK Thickness
Worked example
The values the form comes pre-filled with, run through the tool itself:
| Height | 50 mm |
|---|---|
| Diameter | 200 mm |
| Thickness | 3 mm |
| The flat pattern fits a plate of | 221 × 215 mm |
Frequently asked questions
- Why does the sector sometimes exceed 300 degrees?
- The shallower the cap relative to its diameter, the closer the development gets to a full disc. A very shallow cap can give a sector of 330 degrees or more, leaving only a narrow wedge to remove.
- Which height should I enter?
- The vertical height from apex to rim, not the slant length. The calculation derives the slant from it.
