These are some prints I did a couple of years ago for modifying some expensive plastic components that needed re-machining and couldn't be marked.
The first image is the soft jaws I printed to hold one of the parts, it needed a groove machining internally so the jaws pick up the contours and support the part during the operation. The jaws take only a few hours to print are easily replaced. Since the design work was done I can modify the jaw prints to any odd shapes needing LIGHT machining.
I had another part to modify but it was a different shape, again no visible marks allowed. I could grip this one internally at the rear, but it had a long stick out and being plastic would just distort without support.
I needed to use a large bearing that could be held in the fixed steady, I didn't want to mark or distort the bearing and it needed to locate in the same place each time. A 3D printed collar that was a good press fit with flats that picked up the steady fingers gave me a rigid and repeatable setup.
The final part of this setup was a two piece collet that fitted round the part and pushed into the bearing. I didn't have space in the bearing to go over the external ridges and by having the collet back to a shoulder the part couldn't creep forward during machining.
The soft jaws and bearing support did about 50 parts each, the home made grooving tool also did a good job on all the parts.
It was an end of batch run and the client needed these parts altering to a new design I had done for them before they committed to brand new parts incorporating the new feature. The parts are used in a clinical environment, hence the need to keep them as clean as possible during machining, the printed parts did just that.