Quote Originally Posted by nova_robotics View Post
I bought a little vise for the cross slide on my lathe. You put your part in the vise then put your spinny tool in the chuck of the lathe. I haven't used it yet. I don't know why I bought it. Honestly, why would I ever need this?
If your vice has vertical jaws and will securely and squarely hold the part then there are dozens of reasons why you may want it in the future they just haven't made themselves known to you yet.
I have used tool holders on my tool post as a vice many times this also affords me a limited amount of vertical adjustment as well or clamped a larger part to the tool post itself with a good "C clamp
they are great for finishing out an 80% lower if you don't have a mill or other suitable ridged machine to spin the spinny tool as you called it