Coupling Nuts & Punch Holders

The Cleveland Punch and Die tip of the day deals with the coupling nut. The coupling nut or other means of fastening the punch to the machine is an important consideration to extend punch and die life. Although the coupling nut does not transfer the energy of the machine to the punch, it may prevent the punch from seating squarely against the punch stem. Coupling nut problems such as a worn seat, crushed threads or foreign material in the nut; may cause the punch to cock and strike the die when punching. The simple check of the coupling nut could prevent a costly tooling crash.

Punch holders do not experience a significant compressive force but they do experience a large tensile force. Every time the punch is pulled or "stripped" from the material, a tensile force is generated. This causes the coupling nut to stretch slightly. This stretching is most evident during the punching of thicker material. When the punch is freed from the material, the coupling nut springs back to normal. This rubber band effect will eventually cause the threads of the coupling nut to work lose. For this reason, it is extremely important that the punch holders be checked and tightened on a regular basis.