What is a radius die?
A radius die has machined radius shoulders rather than a sharp V, so it forms a controlled, generous inside radius. It is used where the drawing specifies a large radius, or where a sharp shoulder would mark or crack the material.
When should I use a radius die?
Use one when the required inside radius is larger than an air bending die would produce, when the material must not be creased, or when a heavy section needs the load spread over a wide face.
| Requirement | Why a radius die helps |
|---|---|
| Large specified inside radius | The shoulder radius sets the radius directly |
| Cosmetic outer surface | No sharp shoulder means no shoulder mark |
| Heavy plate | Load spread over a wide contact area |
| Consistent radius over many parts | Radius comes from the tool, not from the forming depth |
How do I check that a radius die suits my machine?
Check the die body width and height against the machine's die rail, the rated load per metre against the calculated force, and the shut height against the punch. A radius die is usually wider than a single-V die of the same opening.
- Body width: the radius shoulders spread the die, so it is wider than an equivalent V die.
- Height: must suit the rail or holder.
- Rated load: the wider contact usually raises it, but check.
- Punch height: the taller die reduces the shut height available.
Does a radius die reduce springback?
It usually increases it, because a large radius means a higher radius-to-thickness ratio and more of the section recovers elastically. Large-radius work needs more overbend or an adjustable die.
Can a radius die form a radius smaller than its shoulder?
No. In air bending the material takes the shape the tooling imposes, and it cannot be formed to a radius tighter than the die shoulder will allow. If the drawing needs a tighter radius, a narrower opening is required instead.
The reverse is possible: with a sharp-shouldered die the radius comes from the material and the opening, which is why the eight times rule produces a radius around 0.16 times the opening.
Related technical pages
Press brake dies
All die types, including single-V and multi-V.
Springback guide
Why large-radius bends spring back most.
Adjustable and multi-V dies
Dies that change their effective geometry.
Custom tooling
Radius dies made to a specific shoulder radius and length.
Next step
Tell us the inside radius on the drawing, the material and the bend length and we will specify a radius die and check the load.
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