Hello Guy. Yes, the clamps are held by friction. The cam action is gentle and varies when measured by around 2mm when measured from the central hole with calipers. I positioned the clamps in the optimum postion for closed (to hold the cube) and drilled the holes for the dogs at that point.
The major difference between the clamps you have shown and these items is the hole placement. In the UJK item it is as near to central as makes no difference. Once tightened against the central dog, there is nowhere for the clamp to move to because it is held against the dog. The dogs do not move when placed in a snug receiving hole made using a highly accurate Forstner bit.
I confess to splashing out and treating myself to these excellent FIsch bits.
sotto voce: If @NewToThis thought £28 for a pencil was expensive, I would not want him to see these bits.
The final part of the equation is a small 20mm hole chamfering tool used to let the chamfer in to rest just at the surface of the wood. I will capture some more up to date images to see if I can demonstrate the fixing and possibly a short video to show how they move.