Pipe-to-square transition

The surface is faceted or triangulated, so the pattern is an approximation. The error is known and printed as a number on the drawing — it is not hidden.

Dimensions are entered as: Inside dimensions. The flat pattern itself is always computed on the neutral fibre — at Ø800 in 3 mm sheet the difference between the inside and the outside dimension is 18.8 mm of developed width, and then the seam does not meet.

Firkant-til-rund overgangskegle med en påsat rørstub: firkantet bund løftes via en trianguleret overgang op til en rund top, hvorpå der sidder en lige rørstub. Overgangen selv er fire plane trekant-flader og fire keglehjørner.

Bruges hvor en firkantet base/kasse skal kobles til et rundt rør via en stub, fx adapter mellem firkantet samlekasse og et rundt tilslutningsrør i ventilation eller aftræk. Klassisk overgangs- og studsarbejde i plade.

VVS-energi og teknisk isolatør — adapter mellem firkantet samlekasse og et rundt tilslutningsrør via en stub; studsarbejde i ventilation og aftræk.

Galvaniseret stålplade 0,7–1,25 mm; rustfri i proces. Overgangen valses, rørstubben rulles.

Source: Materialer/tykkelser: src/lib/kasse/materialer.ts (DIN 6935 for stål; massefylder og handelstykkelser; springback). Ventilation: DS 447:2021 + BR18 §§ 420–452 (src/lib/vvs/artikler.ts). Fremstillingsfælder: docs/PLAN-UDFOLDNINGSBIBLIOTEK.md §9.2/§4.

Firkant-side (bund) — Firkant-side (bund)

Sidelængden på den kvadratiske bund (mm).

Rør-radius (top) — Rør-radius (top)

Radius på den runde top og på rørstubben (mm).

Overgangshøjde — Overgangshøjde

Lodret højde på selve den firkant-til-rund overgang (mm), uden rørstubben.

Rørlængde — Pipe length

Længden på den lige rørstub, der sidder oven på den runde top (mm).

Opdeling/kvart — Opdeling pr. kvart

Antal delpunkter pr. kvart af den runde kant — styrer antal trekanter (uden enhed).

Step by step with compass and square — in cardboard first, in sheet metal after.

1. 01Udvikl overgangsstykket først: tegn den runde top (radius = Rør-radius) i sand størrelse og del omkredsen i 12 med ur-metoden; tegn den firkantede bund (Firkant-side) med dens fire hjørner.
2. 02Læg dem koncentrisk i grundridset og forbind hvert af de 12 runde punkter til de nærmeste firkant-hjørner, så fladen dækkes af trekanter (fire keglehjørner + fire plane sider).
3. 03For hver trekantside laves en sandlængde-trekant: vandret planafstand som den ene katet, Overgangshøjden som den lodrette katet, hypotenusen er den sande længde.
4. 04Læg trekanterne fladt én ad gangen ved at slå buer (cirkelsnit) fra to kendte punkter og finde det tredje i skæringen; forbind de 12 runde randpunkter til en jævn kurve.
5. 05Udvikl rørstubben separat som et lige rør: et rektangel med højde = Rørlængde og bredde = omkreds = 2·π·Rør-radius (parallel-linje-udfoldning).
6. 06Saml stubben på den runde top — pas dens kant til den udfoldede runde kurve — og tilføj limflap/søm langs en lodret kant på både overgang og stub samt fals ved bunden.

Sømmen er bevægelig: brug klokkemålet til at lægge den lodrette samling, hvor det passer bedst. Placér helst overgangens søm midt på en plan side og lad rørstubbens søm flugte med den, så samlingen bliver kort og vandet ledes væk.

• ·To delemner: overgangen (4 trekanter + 4 keglehjørner) OG rørstubben (lige cylinder) — udvikl dem hver for sig og lad sømmene flugte.
• ·Deler du omkredsen i for få stationer, bliver mønstret for lille: korden er kortere end buen. 12 dele er nok til pap, men til plade skal antallet højt (relativ mangel ≈ π²/6N²).
• ·Læg overgangens søm midt på en plan side og rørstubbens søm i forlængelse af den, så samlingen bliver kort.

The words and formulas the trade uses for a flat pattern. The symbols are the same throughout Discebo: α is the bend angle in degrees, R the inside bend radius, t the sheet thickness and K the K-factor — all in millimetres.

Flat pattern (development)

The part's surface laid out flat as one continuous cutting outline — the way the sheet looks BEFORE it is bent or rolled. Only a developable surface can be unfolded exactly; a doubly curved surface cannot be laid flat without stretching the material.

Flat length

The flat length the part must be cut to so the dimensions come out right once it is bent. It is either the sum of the outside dimensions minus the bend deductions, or the sum of the flat legs plus the bend allowances — both routes must give the same number.L = Σ(udvendige mål) − Σ(BD) = Σ(flade ben) + Σ(BA)

Bend allowance

The length of material that sits in the bend itself, measured along the neutral fibre. The bend allowance is always positive and is added to the flat legs.BA = (π/180) · α · (R + K · t)

Bend deduction

The amount subtracted from the sum of the outside dimensions, because the two outside dimensions between them count the corner twice. Here the bend deduction is taken as POSITIVE and subtracted; DIN 6935 writes the same quantity as the compensation value v with the opposite sign.BD = 2 · OSSB − BA

Outside setback

The distance from the theoretical outside corner point in to where the bend starts. Above 90°, tan(α/2) is clamped to at most 1 per DIN 6935, so the number does not explode towards 180°.OSSB = tan(α/2) · (R + t)

Compensation value v to DIN 6935

The standard's own way of writing the same corner loss: the flat length is a + b + v, where v is negative. Our bend deduction is therefore the same quantity with the opposite sign — never flip one without the other.L = a + b + v ⇒ v = −BD

K-factor

Where the neutral fibre sits in the sheet, given as a fraction of the sheet thickness. DIN 6935 writes the correction factor k, which applies to the neutral line in the form (R + t·k/2); the American CAD convention writes (R + K·t), so K = k/2.k = 0,65 + 0,5 · log₁₀(R/t), k ≤ 1,0 ⇒ K = k/2

Neutral fibre

The layer in the sheet that is neither stretched nor compressed when the part is bent. The flat pattern is always computed on the neutral fibre — which is why it matters whether the drawing's dimensions are inside or outside.

Bend angle

The angle the material is turned through, not the angle between the legs. The bend angle is 180° minus the included angle, so a square corner is 90° and a seam fold is 180°.α = 180° − åbningsvinklen

Inside bend radius

The radius on the inside of the bend. It is set by the tooling and the material, not by the drawing — too small a radius cracks the part in the outer fibre.

Sheet thickness

The thickness of the material. It enters every single bend allowance, so sheet delivered 0.2 mm thicker than ordered shifts the flat length at every bend.

Fold line

The line on the flat pattern where the part is to be bent. It is drawn but never cut through — in a laser file it therefore sits on its own layer.

Test bend

A strip of known raw length, bent in the material and the tooling that production will use. Measure the two outside legs afterwards and the bend deduction and K-factor can be worked back. The machine's own measured bend table beats any table.BD_målt = (A + B) − L₀

DIN 6935 covers only cold bending of flat products in structural steel. Stainless, aluminium, copper, brass and titanium zinc are not included — there the formulas are an extrapolation, and a test bend in the actual material settles it.

20 fields. The starting values belong to the figure itself — they live in one place in the code, so the tool, the share link and the smoke test can never disagree about what «default» means.

A preset sets every dimension at once. The name is often the word the part goes by in the workshop — the library's search knows them all.

Read them before the part is cut. They are here because they cannot be calculated away — not as legal text, but as craft.

• The figure supplies the GEOMETRY for both blanks. Air volume, pressure loss, noise and velocity limits belong to the installation's design in accordance with DS 447 (Standard for ventilation systems) and the building regulations' requirements — the tool only calculates the continuity q = A·v and the two equivalent diameters d_e and d_h.
• The transition's pressure-loss coefficient depends on the change in angle and on the flow into the piece. It cannot be derived from the geometry alone and is not given in the figure; look it up in the installation's own documentation or in ASHRAE Fundamentals' fitting tables.
• The transition is developed APPROXIMATELY: the cone-fan arcs are replaced by chords, and the deficit is ≈ Δ²/24 at the angular step Δ. Only the four flat triangles and the pipe neck itself are exact. The error is given as a figure in the key figures and must not be rounded away.
• Edge allowances (bead, seam, flange, overlap, root gap) can be CALCULATED per edge, but not yet applied to the TRANSITION'S triangulated contour. If they are selected there, the cutting file is deliberately blocked — a blank in the wrong size is worse than no file. The pipe neck's edges, on the other hand, can carry an allowance.
• Fire dampers, fire-resistant ducts and penetrations through fire-separating building elements are NOT covered. A fire damper is a certified product to EN 15650, and a nozzle in that zone must be executed according to the damper supplier's installation instructions.
• Hangers, stiffening and leakage tightness are not sized. Duct leakage classes (EN 12237 for round, EN 1507 for rectangular ducts) set requirements for both seams and installation that the geometry does not determine.
• The figure takes no position on corrosion or choice of material in damp, chlorinated or hot environments. The choice of alloy is the user's, and the density follows the selected designation.