- clamp the part directly to table using T-slots with fixture plate or clearance space or sacrificial plate underneath... so you don't mill or drill into your nice table LOL
- mount something like a chuck or collet block to table & chuck holds round-ish work
- mount a smaller toolmaker vise & which can hold rectangular-ish work
- some most? RT's have 2 ground surfaces so they can be positioned in horizontal or vertical plane
- RT can feed continuously like making milling a circular slot, or can be indexed to a specific angle positions using dials or indexing plates if you have them lie doing a radial hole pattern
Kind of depends on your equipment but for example you can mount a plain back chuck to a home made plate & the plate mounts to RT. An advantage here is the plate+chuck assembly can also mount to mill table to hold round parts sometimes better than a vise. Another RT centering technique is to use an arbor blank which has an MT taper on one end to match your RT socket. It is cylindrical on the other end. You insert into RT socket, lightly clamp the chuck jaws to the arbor. Now chuck is pre-centered & you can secure chuck to table (assuming you have that bolt-through style of chuck.
In any case its very important to 1) first center the RT center hole to the spindle using dial test indicator & leave the spindle locked in that XY position. 2) then center the chuck (or more correctly the work within the chuck) to the same quill XY position. Now the part & center axis of RT are coincident.
One of the advantages of a 4 jaw chuck on the RT is you can dial in the work even if the chuck is not 100% centered. Vs. a 3-jaw you must have the chuck properly centered.