Why is a full ring knock-out important?
The main problem with older style knockout cams is that if the brake is poorly adjusted and there is no brake interlock, the press can stop at a point past the end of the knockout cam. In this position the camplate only needs to move a few millimetres away from the flywheel for the clutch key to be released and stroke the press. Often this amount of movement can be done even with a die guard interlock bar in place (ie the press strokes with the guard open). A full ring knockout has additional metal in the bore requiring the camplate to move around 20 mm before engagement can take place. The secondary problem occurs when a brake interlock is fitted. The older style knockout allows the camplate shaft to prematurely start moving back to the disengaged position, allowing the interlock bar to rub on the brake drum inner edge. Prolonged rubbing can wear away the step entirely, leaving nothing to arrest the crank if the slide falls from top centre due to poor brake adjustment or failure.
