Rectangular Tap on Pipe flat pattern

What it is

The rectangular-section collar seated on a shell — the mouth where a rectangular duct enters a round pipe. The catalogue had the round branch on a pipe and the rectangular tube cut by a plane, and did not have the rectangular branch cut by the PIPE.

Where it is used

Intake and grille mouths on pipework, rectangular duct entries into a round header, chutes discharging into a pipe, suction take-offs.

Measurements the calculation needs

• D2 Diameter 2
• X Measurement X
• Y Measurement Y
• C Branch length
• DV Divisions
• THK Thickness

Worked example

The values the form comes pre-filled with, run through the tool itself:

Diameter 2	500 mm
Measurement X	300 mm
Measurement Y	250 mm
Branch length	500 mm
Divisions	16
Thickness	3 mm
The flat pattern fits a plate of	1088 × 283 mm

Frequently asked questions

Are all four walls cut the same?

No, and each pair is cut differently. The two perpendicular to the pipe's axis lie in planes that cut the cylinder in the CIRCLE ITSELF — the bite there is an arc of exact radius. The two parallel to the axis lie in planes that cut the cylinder in STRAIGHT LINES — the bite there is horizontal, the same end to end.

Why only four fold lines?

Because all four walls are flat. A station in the middle of an arc is a marking point, not a fold — only the collar's four corners bend. On a rolled part it is the other way round, which is why the round branch has one fold per station.

And the hole in the shell, is it x by y?

No, and that is the costliest mistake on this part. The hole is a rectangle, yes, but the side that runs across measures the ARC that y occupies on the shell: 2·Rn·asin(y/d2). On a 500 pipe with a 250-wide tap that is 260.2, not 250. Cut it x by y and the hole is narrow and the collar will not go in. The companion part in this catalogue draws the hole already corrected.

Where do I measure the collar length from?

From the AXIS of the pipe to the top face — the centre-to-face dimension, the same convention as the pipe branch. The deepest bite is the radius itself, so the length has to exceed it.