Tablets & Capsules

TC0316

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Tablets & Capsules March 2016 21 W tablet tools Where and how to measure punches and dies Stephen Natoli Natoli Engineering This article clarifies how to measure punches and dies and describes how worn dies can impair production of high-quality tablets. hen it comes to inspecting new and in-process tablet tools, most people focus on the punches. Typically, they use a digital indicator mounted on a granite stand to mea- sure overall punch length and cup depth. Next, they sub- tract the cup depth from the overall length to arrive at the critical dimension: the punch working length. But that can lead to errors because the tolerance for cup depth and for overall punch length is ±0.003 inch, much looser than the ±0.002-inch tolerance for punch working length. Thus if you calculate working length as described above, some tools will appear to be out of spec when in reality they are not. The correct method is to measure the working lengths to see how much they deviate within the set of punches (not between upper and lower). Start by selecting a datum (reference punch) from the set you're measuring. Then compare its dimensions to those of the other punches to see whether they are within 0.002 inch from

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