What is the bending rule?

It's the bender's historic abacus: once you pick the thickness, it shows every usable V-die and, for each, minimum flange, inner radius and tonnage. Here it's digital and driven by the PG SRL technical table, the same one the configurator uses. It gives the full overview, not a single calculation.

Where do the bending rule numbers come from?

From the PG technical table: tonnage per metre tabulated for every thickness by die pair, on reference mild steel UTS≈420 N/mm². They are indicative first-sizing values, not handbook constants: they build in friction, tolerances and real materials.

How is the stainless tonnage calculated?

You start from the carbon-steel tonnage and multiply it by the ultimate-strength ratio, about 1.67 going from 420 to 700 N/mm², then round. It's a conservative estimate: the specific alloy (304, 316, duplex) can swing.

Why is the recommended die V about 8 times the thickness?

In the 1-12 mm band it's the best trade-off between required force, inner radius and grippable minimum flange. Below 1 mm the ratio rises; from 15 mm up it widens to about 10 times to contain force and cracking.

Which formulas does the bending rule use?

Specific force follows t/m = (S² · Rm · 1.6) / (10 · V) with Rm about 420 (carbon) or 700 (stainless) N/mm². Minimum flange is B about V/2 plus support margin, inner radius R about V/8 (air bending, mild steel, indicative), the recommended die V about 8 times the thickness.

Is the tonnage already the force of the bend?

No: it's the force per linear metre (t/m). The total force is t/m times the bend length in metres. A 2.5 m bend at 40 t/m needs 100 t. For the full calculation with your own length use the Bending parameters calculator.

Does the bending rule hold for coining and hemming too?

No, the rule is air bending at 90°. Coining and hemming have dedicated factors found in the Bending parameters calculator.

Does the rule tell me which press brake to buy?

It gives tonnage and geometry per die. For the model with the right margin, with length, volumes and accessories, take the data into the configurator, which sizes the press brake to your work.

Bending rule · Every V-die, flange, radius and tonnage · PG SRL

The bending rule

Thickness S mm

PG technical table — the same used by the configurator

Recommended die

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V ≈ 8 × thickness — the right trade-off between force, radius and flange

V-die	Min flange B	Inner radius R	Carbon steel	Stainless

Tonnage in t/m (per linear metre of bend) · from PG technical table · air bending at 90°, mild steel · indicative values, check with our technical office.

01 — The ruleThe shop-floor rule, digital.

The bending rule is the bender's historic tool: an abacus that, once you pick the thickness, gives you at a glance every usable die (V opening) and, for each, the parameters that matter. Here it is made digital and driven by the PG SRL technical table — the same one working inside our configurator. Pick the thickness at the top and read the full overview: not a single calculation, but every option on the table, with the recommended die already highlighted.

That's the difference from formula calculators: those give you one number at a time; the rule shows you the whole band of choice for the thickness, so you see immediately what changes going from one die to another — and why a narrower or wider V shifts force, radius and minimum flange.

02 — The readingFive columns, one decision.

Each row is a die available for the chosen thickness. The columns:

Column	What it shows
V-die	width of the die opening, in mm — it's the variable that decides everything else
Minimum flange B	the shortest flange the die can grip, in mm — below this size you need dedicated tooling
Inner radius R	the radius formed in air bending at 90°, in mm — set by the die, not the punch
Carbon steel	required tonnage in t/m on reference mild steel (UTS≈420 N/mm²)
Stainless	tonnage in t/m on austenitic stainless — higher, stainless needs more force

The row highlighted in red is the recommended die (V ≈ 8 × thickness): the right starting point in 90% of cases. A narrower V marks the part and raises the force; a wider one lowers it but enlarges inner radius and minimum flange — if your part's flange is short, the wide V won't fit.

03 — The formulasWhere the numbers come from.

The rule's values are tabulated PG technical know-how, not handbook constants. The relationships that govern them, stated:

Specific force t/m = (S² · Rm · 1.6) / (10 · V)

with Rm ≈ 420 N/mm² for carbon steel and Rm ≈ 700 N/mm² for stainless. Force grows with the square of the thickness and drops with the width of the die opening.

Minimum flange B ≈ V/2 + support margin
Inner radius R ≈ V/8 (air bending, mild steel, indicative)
Recommended die V ≈ 8 × thickness

These are first-sizing relationships: the physics underneath is the handbook one, but the numbers in the table build in friction, tooling tolerances and real materials — which is why we mark them as indicative values, to be checked with the technical office, not nameplate truths.

04 — Carbon steel and stainlessWhy two tonnage columns.

For the same thickness and die, stainless needs more force than mild steel, because it has a higher ultimate tensile strength. The rule shows the two columns side by side: the stainless column is the carbon-steel force multiplied by the strength ratio (about ×1.67, from 420 to 700 N/mm²) and rounded. It's a conservative estimate: the specific alloy (304, 316, duplex) can swing. For aluminium, copper and brass the force is instead lower than carbon steel — you'll find those materials in the Bending parameters calculator, which applies the material coefficient to the single bend.

05 — LimitsWhat the rule doesn't tell you.

It's 90° in air: radius and flange hold for air bending at a right angle. Acute angles, coining and hemming change force and geometry — you calculate those in Bending parameters.
It doesn't account for length: tonnage is per metre (t/m). The total force of your bend is t/m × length in metres.
Materials beyond carbon/stainless: aluminium, copper, brass and high-strength steels (Hardox, Strenx) follow different rules on die and radius — they need case-by-case evaluation.
Bends beyond the machine length: you move to a tandem configuration.

Technical note. The rule's values are first-sizing estimates from the PG technical table (air bending at 90°, reference mild steel) and don't replace engineering verification on your drawing and samples. Real forces, radii and flanges depend on material batch, rolling direction, tooling condition and part geometry. For final machine sizing contact our engineering department.

Next step

From the rule to the machine.

You've got the overview of the dies. For the exact calculation of your bend use Bending parameters; to size the press brake, take force and length into the configurator. Or write to us a couple of lines about the part you bend: we reply within 24 hours.

Configure your machine →

Bending rule. Every die, at a glance.