Understanding Press Brake Bending Length and Sheet Thickness
Why maximum thickness depends on bend length, and the other limits buyers overlook.
Press brake brochures quote tonnage and working length, but buyers really think in terms of "what thickness can I bend, and how long?" This article explains how those numbers relate, and what else limits a press brake's capacity.
Tonnage is shared along the length
A press brake's rated force is spread across the bend. Bending 3 mm mild steel takes about 24 T per metre. So a 40 T machine can bend 3 mm over about 1.6 m, but a 2.5 m bend in 3 mm needs about 61 T. In other words, the maximum thickness of a press brake depends on the bend length.
That is why a capacity like "80 T x 2500 mm" does not mean the machine bends any thickness over 2500 mm. It means 80 T is available, and the thickness it can handle over the full 2500 mm is whatever needs 80 T or less.
Capacity of Devraj standard models (mild steel, air bending)
| Model | Force | Working length | Approx. full-length capacity |
|---|---|---|---|
| PBR 215 | 20 T | 1500 mm | about 1.5 mm |
| PBR 320 | 30 T | 2000 mm | about 2 mm (slightly under full length) |
| PBR 420 | 40 T | 2000 mm | about 2 mm |
| CNC 80T | ~80 T | 2500 mm | about 3 mm |
| CNC 125T | ~125 T | 3200 mm | about 4 mm |
| CNC 250T | ~250 T | 3200 mm | about 10 mm (12 mm at the limit) |
| Heavy Duty CNC 400T | ~400 T | 4000 mm | about 12-14 mm |
These are estimates using a die opening of 8 times thickness up to 6 mm and 10 times above that (the wider die is why capacity jumps above 6 mm), with no margin. Thicker sheet can be bent over shorter lengths. Use the tonnage calculator for your own parts.
Other limits besides tonnage
Minimum flange
The flange must be wide enough to bridge the die opening. As a guide, the shortest flange is about 0.7 times the V-die opening. Thick plate needs a wide die, so short flanges on thick plate are often impossible to air bend.
Inside radius
In air bending the inside radius is roughly 16% of the die opening, not the punch radius. If your drawing calls for a tight radius on thick plate, you may need a smaller die and much more force.
Throat depth
Parts wider than the throat depth cannot pass behind the side frames when bending away from the edge.
Open height and stroke
Deep boxes and channels need enough daylight to be removed after the last bend.
Practical guidance
- Decide your thickest regular material and its longest bend first.
- Add about 20% to the calculated force.
- Choose a working length above your longest part.
- Check minimum flange and radius on your drawings.
- For long, thin panels, ask about crowning to keep the angle uniform.