[gtslabs]

I need some advice for surface grinding. I am girding flat the ends of Rock Cores from a drilling operation. I need to hold a tight tolerance of perpendicularity and flatness. However the shaft of the core is not always straight. They are sometimes tapered or bowed and this gives me problems truing the ends. My first step is to secure the piece in my v-block with the bottom elevate off the bed/mag. chuck. I then grind that flat. Next I flip the piece over and put the ground end directly on the chuck and then with down pressure I secure the sample to the V-block and grind the other end.
However at this point any error in the shaft is magnified and my ends do not end up parallel to each other. As I tighten the clamps the pice will lean in against the V-blocks at times. I try rotating the piece and regrinding and it is like chasing my tail at times.

What I need is a way to firmly secure the piece to the chuck at the base but still be rigid enough
to grind without moving the piece. I tried just using the lower set of clamps on my v-block but that did not always work either. My shaft diameter is approximately 1.95" and the length is about 4" - 4.5".

Any ideas on how to remove the irregular part of the shaft and still get a good surface?
I am attaching a picture of my set up. I also checked the flatness of my machine <0.0002 and my V-blocks are perpendicular.

Thanks
Steve