Issue link: https://www.e-digitaleditions.com/i/541292
44 July 2015 Tablets & Capsules Cup depth is the distance between the very tip of the punch and the low- est measurable point of the cup cavity. To establish proper tool inspection protocols and wear limits, you need to know about this dimension and how it affects the tablet. Two standards for tablet com - pression tooling have been published by governed organizations. The first, originally published in 1971, is the "TSM." It ap pears in the American Pharmacists Association's Tablet Specification Manual. It defines the tool- ing format used primarily in the Americas. The other recognized stan- dard, ISO 18084 International Tooling Standard, was published in 2005. It defines the EU tooling for- mat. [Editor's note: For more informa- tion about how the different stan- dards were developed, see the author's September 2010 Back Page article, "Combine the TSM and ISO tooling standards."] In the TSM, cup depth tolerance is ±0.003 inch. But that's for newly manufactured tools, not in-process tools. ISO 18084 makes no reference to cup-depth tolerance or range. Cup depth is integral to overall punch length, and when its tolerance deviates from the standard, so does overall punch length. However, cup- depth variation does not affect the most critical tool length, known as "working length," which is more important than any other punch length dimension, even cup depth. How well punches remain within the given tolerance relates directly to the consistency of tablet weight, hard- ness, and thickness. According to the TSM, the working-length tolerance is a 0.002-inch TIR (total indicator reading). That is the allowable devia- tion within a set of upper or lower punches (not between upper and lower). The TSM does not specify a tolerance for overall punch length, which is a reference dimension. The take-home message is this: Do not measure all three of these punch di - mensions (working length, overall length, and cup depth). One of these three dimensions is always the result of the other two. That's why overall length is defined as a reference di - men sion: It's the result of combining working length and cup depth. The limits of the tolerance Cup-depth tolerance was estab- lished for tooling manufacturers, not necessarily for tablet manufacturers to use as a basis for establishing a protocol to identify out-of-spec tool- ing. In fact, once tools are in service, it's better to apply an in-process range to maintain consistency among the different tablet products you make. Consider, for example, a flat- faced bevel-edge (FFBE) tablet that is 0.21875 inch in diameter, comprises a Schedule II API, and requires a 0.010-inch cup depth. If you adhered to the TSM tolerance, the cup depth could deviate by as much as 30 per- cent from its original value. Now imagine you also compress an over- the-counter (OTC) product that uses a 0.070-inch cup depth. In that case, the allowable deviation would be about 4 percent. Thus a tablet con- taining a controlled substance would get more leeway (allowable devia- tion) than a widely available OTC. Establish a limit Once new tools enter production, they become in-process tools, and manufacturers should establish an appropriate standard deviation that accounts for tool service life and tablet consistency. A reasonable limit is a 15 percent decrease in cup depth from the original specification. Using that limit would keep all your prod- ucts within the same allowable devia- tion, and they would be consistent regardless of the original cup depth. A 15 percent limit would also allow you to polish and maintain tools with deeper cups without wor- rying about diminishing their service life. (Deep-cup tools typically wear more quickly than those with shallow or standard cups, which have a more robust design.) Furthermore, with an in-house standard, you can maintain the tools yourself, significantly reduc- ing costs and increasing efficiency because the tools will remain in ser- vice longer. Furthermore, potent tablets made using shallower cups will be more consistent and closer to specification. T&C [Editor's note: To comment on the Back Page, visit www.tabletscapsules. com.] Dale Natoli is president of Natoli Engineering, 28 Research Park Circle, St. Charles, MO 63304. Tel. 636 926 8900. Website: www.natoli.com. He has more than 35 years' experience in tablet compression tooling and is a member of Tablets & Capsules' Technical Advi- sory Board. b a c k p a g e Cup depth and tablet consistency Figure 1 Adhering to TSM's 0.003-inch allowable cup-depth deviation can give widely different results when applied to deep and shallow cups. Cup depth of 0.070 inch, ±0.003 Cup depth of 0.010 inch, ±0.003 4.3% 30%