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Press Brake V-Die Opening and Minimum Flange Length Chart

Choosing the V die opening is the first decision at the press brake because it sets the inside radius, the minimum flange you can form and the tonnage. This chart gives the common rule-of-thumb values for mild steel in air bending.

Download:
Thickness (mm)V rule (x thickness)Nominal V opening (mm)Min flange (mm), 0.7 x VApprox inside radius (mm), 0.16 x V
0.8
6
6
4.2
1
1
6
6
4.2
1
1.2
6
8
5.6
1.3
1.5
6
10
7
1.6
2
6
12
8.4
1.9
2.5
6
16
11.2
2.6
3
8
24
16.8
3.8
4
8
32
22.4
5.1
5
8
40
28
6.4
6
8
48
33.6
7.7
8
8
64
44.8
10.2
10
8
80
56
12.8
12
10
120
84
19.2

Rule of thumb for mild steel at roughly 400 MPa tensile strength. Use a larger V for stainless and high strength steel, a smaller V for soft aluminum, and always check the tooling manufacturer load chart before bending.

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How to read the chart

Find your material thickness, then read the nominal V opening, the minimum flange and the inside radius the V will naturally produce. A 3 mm steel plate uses a 24 mm V, which makes an inside radius near 3.8 mm and needs a flange of about 17 mm or more. If the drawing demands a smaller radius, you must bottom the bend or choose a narrower V and accept a higher load.

  • V opening is roughly 6 times thickness up to about 2.5 mm.
  • It moves to about 8 times for 3 to 10 mm.
  • It reaches 10 to 12 times for plate above 10 mm.

Why the minimum flange is tied to V

The material must bridge the V shoulders for the bend to form correctly. When the flange is shorter than about 0.7 times the V width, it slips into the die, the bend angle becomes inconsistent and the part can mark or distort. The usual fixes are a narrower V, a shorter flange redesign, a relief, or forming the short flange first and adding it as a separate operation.

Adjusting for the material

Stainless steel and high strength steel need more force and show more springback, so shops commonly widen the V by 10 to 25 percent or accept a larger radius. Soft aluminum can use a narrower V. Treat the table as a starting point for the first piece, then record what actually worked per material, thickness and tool set in your setup sheets or routing notes.

Common mistakes

Using the same V for every thickness in a job family is the most common error. Others include ignoring the tooling manufacturer's maximum load per metre, selecting a V that produces a radius different from the drawing, and designing flanges shorter than the minimum so the part cannot be made without special tooling. Check flange length at quote time, not at the machine.

Frequently Asked Questions

What is the 8 times thickness rule?

It is a common rule that the V die opening should be about eight times the material thickness for mild steel between roughly 3 and 10 mm. Thinner sheet uses closer to six times and very thick plate uses ten or more.

Does a wider V reduce tonnage?

Yes. Required force falls roughly in inverse proportion to V width, but a wider V also produces a larger inside radius and needs a longer minimum flange. The right choice balances machine capacity, drawing radius and flange length.

Can I bend a flange shorter than the minimum?

Sometimes, with a narrower V, special offset or gooseneck tooling, or by bending before other features are added. It raises risk and cost, so flag it during DFM review rather than at the machine.

Is the radius really 16 percent of the V?

For air bending mild steel the natural radius is typically about 15 to 17 percent of the V opening. It varies with material strength and thickness, so verify with a test bend.

If setup times and tooling choices live in spreadsheets rather than your ERP routings, we can help you structure that data for planning and quoting.

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