Flat plate, flange and blank

The surface is developable and the flat pattern is solved in closed form. Cut the part to the drawing and it fits — the whole uncertainty sits in the K-factor, which belongs to the material and the machine, not to the geometry.

Dimensions are entered as: Outside 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 flad plade-ring (flange) med centerhul og en boltcirkel af jævnt fordelte bolthuller midt mellem indre og ydre kant. Et plant emne — mønstret er den sande kontur i 1:1.

Rør- og kanalflanger, blindflanger og monteringsringe der boltes mod en modflange med pakning. Standard-opmærkningsøvelse i deleling af en boltcirkel.

Smed, VVS-energi og industritekniker — rør- og kanalflanger, blindflanger og monteringsringe, der boltes mod en modflange med pakning.

Stål S235 eller rustfri 5–20 mm; skæres/brændes og bores. Boltcirkel efter modflangens standard.

Source: Bærende stål: EN 1090 (smede-artikel i src/lib/skoler/indhold/data.ts + kilder.ts). Materialer/tykkelser: src/lib/kasse/materialer.ts (DIN 6935 for stål; massefylder og handelstykkelser; springback).

Ydre Ø — Outer diameter

Flangens yderdiameter (mm) — den ydre rand af pladeringen.

Indre Ø — Indre diameter (centerhul)

Diameter på centerhullet (mm), typisk svarende til rørets gennemløb. Klampes altid mindre end den ydre.

Tykkelse — Plade-/godstykkelse

Flangepladens tykkelse (mm). Påvirker ikke det plane mønster, kun emnets dybde.

Antal bolte — Number of bolt holes

Hvor mange huller der fordeles jævnt på boltcirklen. 0 = ren ring uden bolthuller.

Bolt-Ø — Bolthul-diameter

Diameter på hvert bolthul (mm). Klampes så hullerne holder sig inden for godset mellem centerhul og yderkant.

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

1. 01Afsæt centrum og slå med passer den ydre cirkel (ydre Ø) og centerhullet (indre Ø) om samme centrum.
2. 02Slå boltcirklen midt imellem: dens radius = (ydre radius + indre radius) ÷ 2.
3. 03Del boltcirklen i 'antal bolte' lige store dele (360° ÷ antal) startende fra en centerlinje, og afsæt et hulcentrum i hvert delepunkt.
4. 04Slå hvert bolthul (bolt-Ø) med passer om sit hulcentrum.
5. 05Kontrollér at hullerne sidder symmetrisk om centerlinjen, og skær yderkontur, centerhul og bolthuller ud i 1:1.

Ved lige antal bolte ligger hullerne parvis over for hinanden — læg ofte to huller om en vandret eller lodret centerlinje, så flangen passer kønt mod modflangen. Kørn hulcentrene før boring, så passeren ikke vandrer.

• ·Ren flad plade i 1:1 — mønstret er den sande kontur; boltcirklen deles i lige store buer med passeren.
• ·Bruges ringen som løfteøje/ophængsplade, er WLL certificeringspligtig (EN 1090) — værktøjet leverer KUN geometrien, ikke bæreevnen.
• ·Bolthullerne skal ligge midt mellem indre og ydre kant (mellem pakning og kant), ellers holder flangen ikke tæt.

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.

25 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 draws GEOMETRY. It does not size: load capacity, bearing pressure at the bolts, tear-out of the material between hole and edge and the plate's deflection have not been calculated. If the plate is to CARRY load, the calculation belongs under EN 1993-1-1/-1-8 (steel structures), and a load-bearing construction product also under EN 1090 with CE marking, execution class (EXC) and welding coordination.
• If the ring is used as a lifting eye/hanger plate, the WLL is subject to certification (EN 1090) — the tool supplies ONLY the geometry, not the load capacity. Lifting gear (eye bolts, lifting brackets, slings, hooks) is CERTIFIED equipment with requirements for WLL marking, traceability and testing in accordance with the Machinery Directive 2006/42/EC. A piece from this figure must not be used for lifting.
• Bolt circle Ø, number of bolts, hole Ø and the holes' clearance (d₀ − d) are INPUT from the mating flange's standard (EN 1092-1 for pipe flanges, ASME B16.5, or the supplier's data sheet). The tool draws what you enter and invents none of the figures — look them up with the supplier.
• Pressure-bearing flanges, blind flanges and covers are pressure-bearing equipment and fall under PED (2014/68/EU) with EN 13445 as the harmonised standard. Material thickness, gasket force and bolt torque are calculated THERE, not here.
• Edge distance (1.5·d for cutting, 2·d for punching), ligament (≥ 1·d, preferably ≥ 2·d) and the smallest punchable hole (Ø ≥ t) are WORKSHOP PRACTICE, not standards. The source of the punching factor is the repo's RIVET_RULES, which is itself marked ‘not standard-backed’. For a load-bearing bolted joint, EN 1993-1-8 table 3.3 applies instead, and it is stricter on capacity than on distance.
• The contour in the pattern and in the DXF is NOMINAL. The cut width has not been deducted: without kerf compensation on the machine, the piece becomes one cut width too small and each hole one cut width too large. For plasma in 20 mm sheet that is 3.6 mm.
• Surface treatment, corrosion class and the sheet's flatness after cutting are not covered. Large thin sheets and narrow rings will warp from the heat of the cut and must be straightened — that is a finishing operation, not a tolerance.