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shortest to longest. Replace the punches that fall outside that tolerance. Punch-tip wear Next, look for wear patterns in other critical areas, such as the punch tips, which can cause tablet defects when worn. Common causes of punch-tip wear include • Combining new punches with worn dies; • Worn die pockets leading to misaligned dies; and • Worn punch guides and keyways leading to mis- aligned punches. When a worn set of dies is used with a new set of punches, it's nearly impossible to obtain the proper clear- ance between the punch tip and the die wall because the gap is too large. That allows powder to slip into the void and create "flashing" during compression (Figure 1). This wayward powder also creates friction and heat, causing the upper punch tip to wear prematurely. That, in turn, can cause the upper punches to bind, which will lead to prema- ture wear of the upper raising cam. If the die pockets, punch guides, or keyways are worn and cause the punch and die to misalign, a j-hook can develop on the punch tip—especially if the cup is deep and there is little land. A j-hook is a small curl or burr that forms on the edge of the punch (photo). This deformation can create capping, in which the top portion of the tablet sepa- rates partially or completely from the remainder, and lami- nation. J-hooks are easy to identify. Using your fingernail, pick at the inner edge of the punch cup to feel whether it has a curled edge. If so, it has a j-hook and the punch must be repaired before you can return it service. The best repair method is to lightly polish the surface of the punch cup and then use an unsewn cotton buffing wheel and a white rouge polish to finish the job. Do not attempt to repair j-hooks using a drag finisher. Not only is that unnecessary, it's counter-productive: You'll over-polish the tool and dull the sharp corners that the punch needs to make good tablets, including the punch-tip relief. Assessing the dies Die-bore wear is a normal result of compressing powders in and ejecting tablets from the die. Abrasive powders, such as those used in some dietary supplements, exacerbate the wear. While you cannot eliminate die-bore wear, you can drastically reduce it by using complementary steel types, tapering the die bore, and/or lining the die with a carbide 22 March 2016 Tablets & Capsules Figure 1 Excessive clearance between a worn die and a new punch A worn die pocket can lead to a j-hook on the punch tip. To remove a j-hook, lightly polish the surface of the punch cup and then buff it using a white rouge polish.