Conical tee (cone branch on a main pipe)
A tee that starts at the main pipe's diameter and narrows to the branch: a reducer with a tee built into it.
How true is the flat pattern?
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.
The vocabulary of bending
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.
The dimensions you type
18 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.
| Dimension in mm | Interval | Standard | Explanation |
|---|---|---|---|
| Dimensions entered asmaal_fra | Cladding dimensions · Pipe + insulation | Cladding dimensions | — |
| Main pipe diameter (inside dimension of the cladding)conditionalD_hoved | 40–1.000 mm · step size 1 | 250 mm | The outside dimension of the insulation on the main pipe. |
| Small diameter (the tee's opening)conditionald | 20–1.000 mm · step size 1 | 120 mm | The cladding's inside dimension where the tee ends. |
| Main pipe outside Ø (bare)conditionalroer_hoved | 10–800 mm · step size 0,1 | 190 mm | — |
| Branch outside Ø (bare)conditionalroer_gren | 10–800 mm · step size 0,1 | 60 mm | — |
| Insulation thicknessconditionaliso | 10–200 mm · step size 5 | 30 mm | — |
| The cone's large endkegle | Main pipe Ø · Own large Ø · Cone slope | Main pipe Ø | — |
| The cone's large Ø at the main pipe's centre lineconditionalD_kegle | 20–1.000 mm · step size 1 | 250 mm | The cladding's inside dimension. At most the main pipe's diameter. |
| Cone slope from verticalconditionalvinkel | 1–60 ° · step size 0,5 | 20 ° | The school's example: Ø250 → Ø120 over a centre length of 180 slopes 19.86°. |
| Length entered aslaengde | Centre length · Short length | Centre length | — |
| Centre lengthconditionalCL | 20–3.000 mm · step size 1 | 180 mm | From the main pipe's centre line up to the tee's opening. |
| Short length KLconditionalKL | 5–3.000 mm · step size 1 | 55 mm | From the top of the main pipe up to the tee's opening. |
| Bead at the tee's openingsik_lille | Over-bead (3 mm) · Under-bead (5 mm) · No bead | Over-bead (3 mm) | — |
| Flange collar against the main pipebertel | 0–20 mm · step size 1 | 10 mm | The school adds 10 mm for the flange collar. |
| Draw the hole in the main pipetegn_hul | on / off | on | The hole in the main pipe's cladding as an extra part: the foot of the cone laid out on the cladding, 1:1. |
| Goods thicknesst | 0,4–1,5 mm · step size 0,05 | 0,7 mm | Sheet jackets are 0.5–1.0 mm. |
| Materiallegering | Aluminium Al99.5 (1050A) · Aluminium AlMg3 (5754) · Hot-dip galvanised steel DX51D+Z · Stainless 1.4301 / AISI 304 · Stainless 1.4404 / AISI 316L | Aluminium Al99.5 (1050A) | — |
Advanced fields
Hidden by default — they have a sensible default, and most parts do not need them.
| Dimension in mm | Interval | Standard | Explanation |
|---|---|---|---|
| Overlap beyond the seam (0 = workshop rule)overlaeg | 0–50 mm · step size 1 | 10 mm | The school goes 10 mm beyond the seam and makes the rivet holes in those 10 mm. |
Ready-made presets
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.
Conical tee Ø250 → Ø120, centre length 180
«Konisk Tee ny w» and the video «Lektion 7 konisk tee plade 3»: small Ø 120, large Ø 250, centre length 180
Also known as: konisk tee 250 120 · konisk T 250
Conical tee Ø250 → Ø120, short length 55
The same tee entered with the short length from the top of the main pipe: 180 − 125 = 55
Also known as: konisk tee kort længde
Reservation
Read them before the part is cut. They are here because they cannot be calculated away — not as legal text, but as craft.
- The cone's axis is perpendicular to the main pipe and passes through its centre line, as in the school's «Konisk Tee» (AMU Syd, sheet metal level 3). An oblique or offset cone is not included.
- The hole in the main pipe's cladding is drawn as a template: the foot of the cone laid out on the cladding. The school does not develop it, so it is pure geometry without allowances.
- A cylindrical branch on a cone (oblique tee on a reducer) is a different figure.