Why does the number of divisions change the result?

Because triangulation approximates the curve with straight segments. More divisions follow the outline more closely; fewer make the pattern easier to mark. For thin plate and large diameters, increase the divisions.

Can this part be rolled?

It is not a surface of revolution, so it does not come off in one pass. In practice it is formed in sections and checked against a template — which is exactly why the flat pattern has to be right before cutting.

Oblique Cone flat pattern

What it is

In an oblique cone the two diameters do not share an axis: one opening is offset from the other. That breaks the symmetry, so the development is no longer an annular sector — it has to be solved by triangulation, dividing the surface into narrow strips and developing them one at a time.

Where it is used

Offset pipe transitions, exhaust manifolds, side nozzles on tanks, connections that must clear an obstruction.

Measurements the calculation needs

D1 Diameter of the bottom mouth
D2 Diameter of the top mouth
H Vertical height between the mouths
DV Divisions
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:

Diameter of the bottom mouth	800 mm
Diameter of the top mouth	1200 mm
Vertical height between the mouths	800 mm
Divisions	16
Plate thickness	3 mm
The flat pattern fits a plate of	2546 × 2357 mm

Result of the example

Plate	2546 × 2357 mm
Area and weight	2.62 m² · ≈ 61.6 kg in 3 mm steel

Oblique Cone flat pattern: drawing of the template with the worked example dimensions — Cut lines in purple, welds in green and reference lines in orange. Plate 2546 × 2357 mm.

Guides about this part

Frequently asked questions

Why does the number of divisions change the result?: Because triangulation approximates the curve with straight segments. More divisions follow the outline more closely; fewer make the pattern easier to mark. For thin plate and large diameters, increase the divisions.
Can this part be rolled?: It is not a surface of revolution, so it does not come off in one pass. In practice it is formed in sections and checked against a template — which is exactly why the flat pattern has to be right before cutting.

Oblique Cone dimension drawing: D1 (Diameter of the bottom mouth), D2 (Diameter of the top mouth), H (Vertical height between the mouths), DV (Divisions), THK (Plate thickness), marked on the part

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You can work out the figures right here, with no account. PDF, DXF, 3D and history take an account — free, with unlimited calculations.