Two clamping tips
The t-nuts for my drill-mill are threaded 12 mm. So from 12 mm threaded rod I made little pieces with inner threads of 6 and 8 mm. See picture 1. Now I can clamp a work piece with a counter sunk hole and mill it without being hindered by clamping bars.
To clamp small work pieces I drilled holes in a toolmaker clamp. Combined with the fore mentioned inner threaded things I can clamp side ways. See picture 2 and 3.
picture 2: picture 3: