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Clearance of die sections, for the release of slugs, has always been a problem to die making. When die sections were filed and broached the angle of taper was in excess of 1°. (see A above) This allowed the slug to pass through the die section with comparative ease. Sharpening of the section increased the clearance and added larger and larger burrs to the edges of the part. This shortened the life of the section, which then had to be replaced.

Form grinding changed the way die sections were created. The contour was ground with the proper clearance straight through and then a clearance angle was added. (see B above) Usually this was ½° per side ¼" from the top of the die surface. Grinding the section twice added to the expense of making the section, but made repeatability of geometry of the sections easier to replace. It also slightly increased the pressure required to force the slug through the die. Another draw back was that, as the die sections cutting edge wore, the pressure required was further increased. The slugs being pushed through the die section burnish the sides of the section to a reverse angle. This increases the pressure required for the punch to force the slug through the die section

With the advent of Wire Electrical Discharge Machines (WEDM) the die sections were made with the clearance angle already incorporated onto the geometry of the cutting edge. (see C above) This allows for less pressure to force the slug through the die section. When sharpening the section, stock removal is minimized due to the absence of burnishing of the walls. The clearance angle is reduced to 0.3° for a total of .005" per inch of die height. This extends the life of the die section even though replacement is simpler and less costly than the other two methods.

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