Very good idea to use plastic clamps and bolts. I also print T-nuts and other special holders for my currently ongoing DIY 3D printer project and I find them very strong and reliable, so I will probably not buy more T-nuts. I print mine with 3, 4 and 5mm nut inserts, depending on the need, and use ordinary nuts. OK, it's not steel but some times you don't need steel and PLA is in fact strong enough for this type of work, and as you already noted, it does not break your expensive cutter... I haven't used any 3D printed parts on my CNC yet, but I think it's a good idea and will probably print some for PCB and acrylic clamping.