Conic Bending Dimensions
Technical Drawing
Input Values
Results
Calculation Steps
Frequently Asked Questions
What is a cone flat pattern?
A cone flat pattern, or cone development, is the 2D shape of the sheet metal that can be cut and rolled to form a 3D cone without stretching or compressing the material.
How accurate are these calculations?
The calculations are based on the neutral axis of the material thickness, providing a theoretical flat pattern. For precision work, fabricators may need to make minor adjustments based on specific material properties and bending techniques.
The Cone Development Principle
A conical part such as a reducer, hopper, or transition piece is made by cutting a flat sheet and rolling it into a cone. Because the sheet is neither stretched nor compressed, the 3D surface must be “developable” - it can be laid out flat without distortion. For a frustum (a cone with the tip cut off) the flat pattern is a sector of an annulus: an arc for the small rim, an arc for the large rim, and the slant height between them. Getting these numbers right up front saves both material and rework on the bending bench.
Key Dimensions and Formulas
The tool starts from the top and bottom outer diameters Dc1 and Dc2 and the cone height Hc. It first derives the slant height Rp of the frustum, then the rim circumferences Sp1 and Sp2. From these it calculates the sector angle A of the development, the inner development radius Rp1 and outer radius Rp2, and finally the bounding flat plate length Lp0 and width Wp0. A cutting-space margin (Space) is added on each side to give the finished blank dimensions Lpf and Wpf used for ordering material.
Material and Weight Estimation
With material thickness Tp and the selected density (structural steel, aluminium, or stainless steel) the calculator returns two weights: the flat blank weight, based on the rectangular sheet you actually cut, and the bent cone weight, based on the true conical surface area. The difference between the two is mostly the corner scrap of the rectangular blank - useful for cost, logistics, and scrap reporting before you quote a job.