GN 927.2 Clamping Levers with Eccentrical Cam with Internal Thread

Clamping levers with eccentrical cam GN 927.2 are used for rapid clamping and releasing. Contrary to a clamping operation via a thread, these levers permit torque-free clamping.

The lever has been designed to ensure that its movement cannot exceed the max. clamping force. There are no loose components since they are all assembled and mounted in their correct order.

To achieve maximum clamping forces, the clamping surface is lightly greased and should be relubricated as required.

Type A has the following advantages: The distance between the eccentrical cam and the contact surface is adjustable by means of a fine threaded setting nut. This allows the max. clamping force to be set by a simple adjustment. In addition, this also allows the choice of the preferred lever position in relation to the clamping lever pin.

• Constructional Features 

• Clamping and Manual Forces 

• Clamping surface free of grease

• Other finishes

General information

The eccentric principle has two advantages: A large clamping force F_s and a self-locking mechanism as soon as the dead centre is exceeded.

All theoretical attempts to describe the ratio between manual and clamping force will ultimately rest only on assumptions in some parameters. The actually prevailing conditions are influenced by a number of different factors.

The values given in the tables below are therefore based on practical specifications and findings and rest on test series which have shown which clamping forces can be achieved by applying the specified manual forces.

The maximum permitted pretensioning force of each thread size will not be exceeded by operating the lever.

 

Clamping and manual forces

Calculation

To account for the above theoretical and arithmetical alternative for determining clamping and manual forces, a potential solution will be shown below which will ultimately also prove the plausibility of the values given in the table using a calculation example.

When theoretically determining the clamping force F_s resulting from the manual force, two points must be observed in particular:

First, there are the geometrical conditions existing at the eccentric which call for an arithmetically complex approach if one wishes to take account of the exact conditions. Secondly, the friction occurring at several points will have a strong impact on the achievable clamping force.

1st alternative, eccentric

Looking at the developed view arising in an eccentric through the rolling motion, one will find that this is caused by a sinusoidal curve.

The result is that the gradient angle w above the swivel range changes permanently, causing an extension of the self-locking range and of the force transmission.

However, the arithmetical description of this approach is highly complex.

 

Substitute calculation model

In simple terms and assuming a constant gradient, the existing sine curve may be seen as a wedge which will result in a sufficiently accurate and approximate substitute calculation model which is a great deal less complex.

A friction value will be assumed for the axis of rotation and the circumference of the eccentric, which will in reality be strongly influenced by external factors and may therefore diverge accordingly.

2nd alternative, eccentric

 

Equations and model calculations

Safety notices

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