Neo,
I have several sets of those types of clamps made up from my apprentice days. I am not sure where they are hiding (my shop, which sets up nicely in 2500 ft² is currently crammed into 880 ft² and spread across two storage units in boxes). Basically, the t-slot clamp itself is made to make a minimal protrusion from the table and sit back some distance (at least 1/4 inch or 6 mm) from the work. On the "fixed" side, an insert fits into the t-slot clamp with a dowel pin to maintain axial rigidity. On the "clamp" side, an insert fits onto a pivot (I used dowel pins) such that it can "swing down" to clamp. The "inserts" are sacrificial such that milling through them is not a problem.
A variation on this I have used several times is to make a "clamp bar" that has angled faces (30° each way) that mates into the "t-slot clamp" and "pusher bar" (which is then U shaped) through equally angled faces to spread the "pusher bar" as the "clamp bar" is tightened. I find this an easier to make & maintain type of mini-clamp. You just have to allow the side-to-side motion as the angled faces move when tightening.
The sacrificial inserts should be made from the same material as the part being clamped.
Does this help?
