How is this different from the oblique cone already in the catalogue?

It is not, when the offset is exactly the difference between the two radii. The oblique cone is this same cone with the offset locked at that value, which is what leaves one generatrix vertical. Here the offset is yours, so one page covers the concentric case, the tangent one and everything between.

Why is the flat pattern triangulated rather than a compass sector?

Because only the concentric cone is a right circular cone, and only it opens into a sector of a circular ring. Shift one mouth and the generatrices stop converging on a point, so the only exact layout is to join the two mouths with true-length triangles. The pattern stays exact; what changes is the method.

Can the offset go past the point where the mouths become tangent?

It can, and that is a catalogue part in its own right. Past the tangent the top mouth leaves the footprint of the bottom one, the part stops having a plumb side and starts leaning both ways. The calculation is the same.

Offset Cone flat pattern

What it is

The offset cone is the reducer whose two mouths are parallel but not coaxial: the top one is shifted by an amount you enter. At zero offset it is the concentric reducer; at the offset where both mouths become tangent on the same side, it is the eccentric reducer with one side plumb; and beyond that it is what the shop calls an external eccentric, with the top mouth outside the footprint of the bottom one.

Where it is used

Axis offsets in pipework where the reducer also has to shift the line, transitions between misaligned nozzles, connections that clear a beam or a piece of equipment, hopper bottoms with the outlet off centre.

Measurements the calculation needs

D1 Diameter of the bottom mouth
D2 Diameter of the top mouth
H Vertical height between the mouths
V Offset between the axes
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
Offset between the axes	100 mm
Divisions	16
Plate thickness	3 mm
The flat pattern fits a plate of	2555 × 2449 mm

Result of the example

Plate	2555 × 2449 mm
Area and weight	2.59 m² · ≈ 61.0 kg in 3 mm steel

Offset 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 2555 × 2449 mm.

Guides about this part

Frequently asked questions

How is this different from the oblique cone already in the catalogue?: It is not, when the offset is exactly the difference between the two radii. The oblique cone is this same cone with the offset locked at that value, which is what leaves one generatrix vertical. Here the offset is yours, so one page covers the concentric case, the tangent one and everything between.
Why is the flat pattern triangulated rather than a compass sector?: Because only the concentric cone is a right circular cone, and only it opens into a sector of a circular ring. Shift one mouth and the generatrices stop converging on a point, so the only exact layout is to join the two mouths with true-length triangles. The pattern stays exact; what changes is the method.
Can the offset go past the point where the mouths become tangent?: It can, and that is a catalogue part in its own right. Past the tangent the top mouth leaves the footprint of the bottom one, the part stops having a plumb side and starts leaning both ways. The calculation is the same.

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

Calculate here, no account Open the full calculator

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