A while ago I modified an 8" C clamp to make releasing tooling from my MT3 spindle easier: http://benchtopmachineshop.blogspot.com/2013/06/mill-mt3-spindle-release.html. It worked OK, but the clamp would frequently slip off the drawbar or the clamp would slide to one side.
To fix it I removed the pad from the clamp, leaving just the ball. I then turned a spherical dimple in the top of the drawbar roughly the same size as the ball on the clamp. Now the ball mates to the drawbar and keeps it from sliding and directs all the force downward.
It's made the tool work much better and it's a breeze to release my MT3 tooling now.
|Clamp with the pad removed from the screw, exposing the ball.|
|Dimple in the top of the drawbar which captures the clamp's ball.|