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Why are the jaws of Piher clamps not parallel? The Compensation Angle

Angulo de compensación de PIHER

— I have received my PIHER clamp but I see that the clamp is not perfectly aligned at 90° to the bar.
Non high-quality clamp jaws are perfectly parallel. If so, it would be a mistake.

— Why?
All materials flex when pressure is applied to them. As time goes on, as we work with the clamp and apply pressure to it, the angle of alignment of the jaws will increase because of this flexing. When manufacturing the clamp and determining the position of the jaws, this deflection must be taken into account and compensated for.


Angulo de compensación de PIHER

To compensate for this bending of the material, when aligning the clamping jaws, we apply the“compensation angle”, i.e. the margin that corrects the potential bending of the material due to the pressure and ensures that the tool functions correctly, maintaining constant pressure and perfect clamping. In the Piher laboratory, we calculate that the parallelism between the jaws is close to the bending limit in order to prevent the clamp from being ejected during work. In this way, the clamping capacity is guaranteed for as long as necessary.

If we do not have this compensation angle when manufacturing the clamping jaws, the final angle we will obtain will be greater than 90º.

– What’s wrong with that?
If the angle is greater than 90º, the pieces being clamped will tend to be pushed out of the clamp by the pressure. If the alignment angle of the jaws is kept at less than 90º the clamped material will remain fixed. We can say that there is a rule that for the clamping to be fixed the alignment of the jaws must be ≤90º.


Angulo de compensación de PIHER

– How much angle compensation is applied at PIHER?
Piher applies a compensation angle of approximately 1°. In other words, the jaws are aligned with the bar at approximately 89º.


Angulo de compensación de PIHER

– Has this angle always been used?
Yes, and not only by Piher, but any manufacturer of quality clamps also has to apply this angle. If the manufacturing is correct, in any quality clamp its jaws have less than 90º angles. None of them fabricates parallel jaws (except for the parallel models manufactured for that purpose).

– Does this also apply to clamps with swivel pads?
Both the piston clamps and the classic clamps with swivel pads include this angle compensation in their jaws. However, the fact that the latter has a tilting pad influences the application of the ≤90° rule for better clamping. As the pad tilts, the final clamping angle is not necessarily the same as that of the jaws. Therefore, when clamping parts that are not exactly parallel, the final clamping angle will not be correct and may move or come off.

In addition, the swivel pad rotates against the material while we apply pressure, causing the piece to move. With the piston system, there’s no twisting at all.

With the piston system the pressure, the piston that applies the pressure copies exactly the angle of the movable jaw and, together with the angle of the fixed jaw, reaches the ≤90º rule. This angle allows us to set the clamp at the exact point where we want to apply pressure, both on parallel and inclined surfaces, even on rounded surfaces.



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