Check the Clearance!

The Cleveland Punch and Die tip for the day deals with the clearance between the punch and die. The clearance not only affects the punch and die life, but also the appearance of the hole. The clearance is determined by material thickness as well as the type of material being punched. Using correct clearance will result with approximately the top one third of the hole measuring the size of the punch and the bottom two thirds flaring to the approximate inside diameter of the die.

Insufficient clearance usually causes a secondary shear to be generated, resulting in additional wear on the punch and thus reducing punch and die life. Excessive clearance may result in a large flaring or "blow out" as well as a burr on the bottom of the material. Material "roll-over" may also occur along the top edge of the hole which will cause the punch's sharp edge to break down rapidly.

This figure shows an example of the effects of excessive and insufficient clearance:

No exact science exists for determining the proper clearance between the punch and die. What may work well for one particular type of material may be unsuccessful for another. However, the following chart provides good guidelines when punching A-36 mild steel:

    Material Thickness                     Die Clearance

1/4" up to 1/2"                              1/32"

1/2" up to 3/4"                              1/16"

 3/4" up to 1"                                 3/32"

1" and over                                  1/8"

When punching material other than mild steel, refer to the follow table:

Following these clearance guidelines will surely increase the life of the punch and die, resulting in "More Holes Per Dollar".