V-die selector
The press brake V die opening you pick sets the inside radius, the spring-back you have to fight, and the tonnage the job needs. It is the most consequential tooling choice on the machine. Most press brake v opening charts assume air bending — if you bottom or coin, the numbers move.
Rule-of-thumb values, not a specification. The 8 × thickness starting point is the usual published figure; actual choice depends on the alloy, the radius you need, and the punch and die you have. Confirm against your tooling maker's chart.
What the V-opening decides
Three things move together when you change the V. A wider V needs less tonnage and produces a larger inside radius — but it also gives the material more room to spring back, so the angle you set is less likely to be the angle you keep. A narrower V holds the angle better and gives a sharper radius, but demands more force and raises the risk of cracking on harder material.
This is why one die does not cover everything. A shop working across a range of thicknesses usually ends up with two or three V sizes rather than one compromise.
The minimum bend flange, and why it bites people
The flange has to be long enough to sit on the die shoulders. If it is shorter than roughly half the V-opening plus the thickness, the part drops into the V instead of bending, and no amount of tonnage fixes it. Shops discover this after the machine is on the floor, usually on a job that needs a small return flange.
The workarounds are a narrower V, a shallower flange with a larger radius, or a different punch profile entirely. Knowing the limit before you order tooling is cheaper than finding it on the first part.
Reading the tonnage figure
The tonnage-per-foot row uses the same air-bending relationship as thetonnage calculator, holding the V you selected. Halving the V-opening roughly doubles the force for the same bend — that is the trade you are making when you go tighter for a sharper radius.
Stainless and aluminium behave differently from mild steel at the same gauge. Stainless springs back more and usually wants a tighter V or a bottoming hit to hold angle; aluminium is softer, needs less force, and marks more easily, which makes the die surface finish matter more than people expect.
Ask us which die to order with the machine
Tell us the thickness range you work in and the tightest bend flange you need to hold. We will suggest a V-die set that covers it, and it ships with the machine rather than after it.