how to calculate the clamping force?
The clamping force will be many times the force that is applied to the handle. It depends on how the clamp is adjusted. But I'm sure you know this already. This is how I would calculate the force:
1. Set the clamp in its over-centre position.
2. Reset the clam in an under-centre position with the same angels.
3. Resolve the forces on the handle to work out the force that the handle applies to the clamping lever.
4. Reset the clamp to its over-centre position.
5. Apply the force calculated in step 3 to the clamping lever.
6. Resolve the forces in the clamping lever.
I hope this helps.