Elliptical cone

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.

En elliptisk kegle: en kegle hvis grundflade er en ellipse i stedet for en cirkel, med spidsen lodret over ellipsens centrum. Fordi generatricerne ikke har samme længde hele vejen rundt, kan den ikke udvikles som en ren sektor.

Overgange fra en oval/elliptisk åbning til et punkt eller en studs — fx ovale emhætte-tragte, elliptiske indløb og overgange hvor pladsen kræver et fladtrykt keglesnit.

VVS-energi og teknisk isolatør — overgange fra en oval/elliptisk åbning til en studs; smed/metalsmed på fladtrykte keglesnit, hvor pladsen kræver det.

Galvaniseret eller rustfri tyndplade 0,7–2 mm. Trianguleres og valses.

Source: Materialer/tykkelser: src/lib/kasse/materialer.ts (DIN 6935 for stål; massefylder og handelstykkelser; springback). Fremstillingsfælder: docs/PLAN-UDFOLDNINGSBIBLIOTEK.md §9.2/§4.

A-radius — Halvakse A

Ellipse-grundfladens halve bredde langs den ene akse (X) i mm.

B-radius — Halvakse B

Ellipse-grundfladens halve bredde langs den anden akse (Z) i mm.

Højde — Vertical height

Den lodrette afstand fra grundfladen op til spidsen (apex) i mm.

Sider — Facettering

Antal flader modellen tegnes med (visning). Højt tal = glat overflade; lavt tal = synlige facetter.

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

1. 01Tegn ellipse-grundfladen i plan i 1:1 ud fra halvakserne A og B, og marker spidsens placering (over centrum) i opstalten.
2. 02Del ellipse-randen i lige mange punkter rundt om (fx 12) — bemærk at buelængden mellem punkterne varierer, fordi det er en ellipse, ikke en cirkel.
3. 03Forbind hvert randpunkt med spidsen; hver generatrix bliver en trekant med to nabopunkter på randen.
4. 04Find hver generatrices sande længde med en sandlængde-trekant: planafstanden fra punkt til centrum vandret, højden lodret, hypotenusen = sand længde. Find også de sande korder mellem nabopunkterne på randen.
5. 05Læg trekanterne fladt én ad gangen fra sømmen: slå en bue med den sande generatrix fra spidsen og en bue med den sande korde fra forrige randpunkt (cirkelsnit), og afsæt skæringen.
6. 06Forbind randpunkterne med en jævn kurve til mønsterranden og læg sømtillæg langs startkanten.

Sømmen er bevægelig: læg den helst ved en af ellipsens akse-ender (kortakse-enden giver den korteste, mest stejle generatrix), så samlingen bliver nem og symmetrisk.

• ·Generatricerne har IKKE samme længde hele vejen rundt, så figuren kan ikke udvikles som en ren sektor — hver station trianguleres for sig.
• ·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).
• ·Notér valseretningen: aluminium og titanzink revner ved buk LANGS valsningen (fordobl radius), og slebet rustfri/kobber/zink giver skakternet facade ved 90°-drejning.

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.

12 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 calculates GEOMETRY. A conical shell in pressure-bearing equipment must be verified in accordance with EN 13445-3; an elliptical shell is not an axisymmetric shell, and the standard's conical formulas do not cover it without a separate FEM verification.
• The tightness of an oval ventilation transition is not geometry. Ducts must meet the leakage class in EN 12237 (round) or EN 1507 (rectangular) respectively, and a seamed joint without sealing does not hold class C.
• Chimney and flue pipes are certified equipment (EN 1856-1/-2). An oval conical transition in a flue must not be manufactured according to this figure.
• The angle of repose for a bulk material is an INPUT from the supplier. An oval hopper has TWO flank angles (at the major and minor axis) — the flattest must be steeper than the angle of repose, otherwise the material will bridge over.
• Eccentric (oblique) cones have UNEQUAL-length generatrices. If the piece is to be rolled, the roller must be set to each individual generatrix; a cone roller with one setting produces a right, symmetrical cone.
• The development is APPROXIMATE (triangulation development): the base's arc is replaced by chords, and the deficit ≈ Δ²/24 is given as a key figure. For sheet metal the division should be at least 180 stations.
• The insulation shell's overlap against the adjoining piece follows BAI's trade agreement and is set in the workshop's overlap rule — the figure does not calculate it itself, and an overlap will block the cutting file.
• Wind load, snow load and support of a free-standing oval cone (hood, hopper roof) are NOT covered. It is a building component and must be verified in accordance with EN 1991-1-3 and EN 1991-1-4.