What is multistep radius bending?

It's the technique to get a large radius by making many small bends close together at a constant pitch, with a standard punch and die, instead of a dedicated radius punch. In English it's called bump bending or step bending.

How many hits for a smooth radius?

Rule of thumb: 1.5–2 degrees per hit, with a pitch between 2 and 5 mm. For a 90 degree arc that's about 45–60 hits. More hits make the curve smoother but lengthen the cycle; the calculator shows the deviation from radius and a traffic light for the trade-off.

How are you different from competitors' calculators?

Competitors give only angle per hit and pitch. We give the full step table with the back-gauge value for each hit, the diagram of the radius forming and the faceting check: the ready-to-follow sequence for the machine.

Which die and punch do I use for bump bending?

You use an open V-die and a punch with a small standard radius; the final radius depends on pitch and angle per hit, not on the die. The exact choice depends on thickness and material: use the bending parameters calculator for die and tonnage.

Can I do bump bending on PG presses?

Yes. You need a CNC with a motorised back gauge to position the sheet at the right pitch on each hit: all PG press brakes (DCA, H.DCA, E.DCA) have it as standard.

Radius bending calculator (Calendering) · Steps, angle, pitch

Your radius bend

Circle mode · the fields of the Calendering function on PG presses

What you set

Inner radius Ri mm

The large radius you want. K 0.50 · neutral axis at K·S from the inside.

Arc angle degrees

How far the radius turns in total. 90° = quarter curve · 180° = half pipe.

Thickness S mm

Number of hits n

More hits = smoother radius, longer cycle.

Angle per hit degrees

Typically 1.5–2° for a smooth curve. The number of hits follows.

Back-gauge pitch mm

How much you advance the back gauge each hit. The (integer) number of hits is derived from this, like the press's Calendering function: the real pitch may round a little.

Back-gauge pitch

—mm

how much to advance the back gauge between hits

Number of hits

—

total hits to close the arc

Angle per hit

—°

arc ÷ number of hits

Arc development

—mm

length of the curved zone on the blank

Deviation from radius

mm

faceting depth

Need force and machine?

Bending parameters calculator

Here you have the geometric sequence. For the tonnage of the single bend, the V-die and the PG press with the right CNC and motorised back gauge for bump bending, use the main calculator.

Calculate force and machine → or request a quote

Hit sequence

the back-gauge column is the value to set on the CNC, hit after hit

Hit	Cumulative angle	Back gauge	Pitch

01 — Bump bendingA radius made of many bends.

To get a large radius — larger than a normal punch would give — you don't need a dedicated radius tool: you make many small bends close together, all equal, at a constant pitch. This is multistep radius bending (or bump bending). Each hit bends a few degrees; adding up the hits forms the curve. The closer the hits, the smoother the curve.

The advantage is flexibility: with the same V-die and a standard punch you get any radius, without buying a tool for every size. The price is cycle time (many hits) and a slightly faceted surface, which the calculator helps you keep under control.

On PG presses this function is called Calendering: it's the press's CNC that generates the sequence of sub-bends from the few values you set. This calculator reproduces the Circle mode — radius + angle → circular trajectory — and uses the same fields: radius, angle, step, number of hits, development. PG's Calendering also offers 3-points and custom modes.

02 — The formulasAngle, pitch, development.

Three numbers govern everything. The angle per hit is the total arc divided by the number of hits. The pitch is how much to advance the back gauge between hits, measured on the development (neutral axis at Ri + K·S). The arc development is the sum of the pitches:

angle/hit = arc ÷ no. of hits
pitch = (π / 180) · (angle/hit) · (Ri + K · S)
arc development = no. of hits · pitch

Example: inner radius 100 mm, arc 90°, thickness 3, 45 hits → angle/hit = 2°, pitch ≈ 3.5 mm, arc development ≈ 159 mm. These are the same public formulas everyone uses (DIN for the K-factor, arc geometry); the difference is that here we give you the full table, not just the two values. The pitch is the arc development divided by the number of hits — the same logic as PG's Calendering function.

03 — How many hitsSmooth vs fast.

This is the real trade-off of bump bending. More hits = smoother radius but longer cycle; fewer hits = faster but faceted surface. The shop rule: keep the angle per hit around 1.5–2° and the pitch between 2 and 5 mm. The deviation from radius the calculator shows is the faceting depth: below a few tenths of a millimetre the curve looks smooth to the eye and the touch.

Under the results panel there's also a traffic light: green when the angle per hit is below 2°, amber up to 4°, red beyond — where the radius stays visibly faceted.

04 — The tableOne row per hit.

The hit sequence above is what you take to the machine. Each row is one hit: the cumulative angle (where you are along the arc), the back gauge (the value to set on the CNC for that hit) and the pitch from the previous hit. Set the back gauge to the listed value, strike, advance to the next row. No mental maths and no cumulative errors: competitors give you only the angle and the pitch, we give you the ready-to-follow list.

05 — LimitsWhen to validate.

The calculation is geometric and indicative for air bending on mild steel. Springback adds up hit after hit: in practice you set a small over-bend per hit, to be tuned on the material. The choice of die and punch, the behaviour on stainless and high-strength steels and very tight radii shift the result. Use this tool to set up the job, then verify on a sample or with our technical office. For force, die and machine switch to the bending parameters calculator.

Radius bending. Hit by hit.