What is crowning on a press brake?
Crowning compensates for the deflection of the ram and the bed under load. Without it, the middle of a long bend receives less force than the ends, so the bend is shallowest in the centre. Crowning adds a matching curve so the load is even.
Why does a long bend come out shallower in the middle?
Under load the ram and the bed bend apart, so the die opening effectively grows towards the centre of the machine. The material in the middle is then bent less than the material at the ends.
- The effect grows with the bend length, the material thickness and the material strength.
- It is invisible on short bends and obvious on full-length work.
- It is the most common cause of an angle that varies along the length.
- It is corrected by crowning, not by adjusting the depth.
How is crowning applied?
Three methods are in use: a mechanical wedge table that is set by hand or by motor, a hydraulic crowning system built into the bed, and the older method of shimming the die. The first two can be adjusted for the job; shimming is fixed.
| Method | How it is set | Typical use |
|---|---|---|
| Mechanical wedge table | Hand or motor driven wedges | Common on mid-range machines |
| Hydraulic crowning | Pressure in cells along the bed | High-accuracy and CNC machines |
| Die shimming | Shims under the die | Older machines, fixed jobs |
| CNC controller assisted | Control calculates from the job data | Machines with the feature fitted |
How much crowning does a job need?
Enough to match the deflection the load produces, which depends on the bend length, the thickness, the material and the die opening. It is normally set from the machine's crowning chart or calculated by the controller, then confirmed on a trial part.
Does crowning affect short bends?
It has little effect, because there is little deflection to compensate. Over-crowning a short bend can make the middle too deep, which is why crowning has to be set for the job rather than left at a default value.
A good practice is to set crowning from the job data, then check the trial part at both ends and in the middle before running production.
Related technical pages
Tonnage calculator
The load that produces the deflection.
Tooling setup guide
Setting crowning as part of the setup.
Troubleshooting
Diagnosing an angle that varies along the bend.
Press brake dies
Die body stiffness, which also resists deflection.
Next step
Send the machine, the bend length and the material and we will advise on crowning and tooling for full-length work.
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