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​Cup and Tablet - Depth and Consistency


The cup depth is the space between the punch tip and the lowest possible measurable area of a cup cavity. In order to form proper inspection and wear limits of the tooling equipment, it is important that one should know about it, and how premature wear can affect the tablet.

Two guidelines that one can follow about tablet compression tooling have been published. Originally published in 1971, the first standard appears in the American Pharmacist Associations tablet Specification Manual – the TSM. The TSM defines the format of the tooling that is used in the Americas. The second one is the ISO 18084 International Tooling Standard, which defines the EU tooling format. In the TSM manual, the cup depth tolerance is set at +/- 0.003 inch. This tolerance is set for new tools and not in-process tools. The ISO 18084 do not refer over the cup depth tolerance or the range.

The cup depth is essential to the overall punch length and when the tolerance changes or deviates from the standard set the overall punch, length is affected. That said, the variation does not affect the “working length” which is the most important length tool of the tooling equipment. The tablet’s consistent weight, hardness and thickness show how well the punches remain within the tolerance level.

According to the TSM manual, the working length tolerance should be 0.002 inch TIR that is the allowable deviation that lower/upper punch can deviate in. That said, the TSM do not specify a tolerance for the overall punch length, which is the reference dimension. As such, one does not need to measure all of the three punches, as one of the dimension is the result of the other two. The overall length therefore is the combination of the cup depth and the working length.

Tolerance Limit

The cup depth tolerance was developed for tooling vendors and not specifically for tablet manufacturers as it is used as a way to identify out of spec tooling equipment. Once the tools are used in production, it is important to consider an in-process range, which would help maintain the consistency of several products that the company produces. An example is a flat faced bevel edge tablet that has 0.21875 inch in diameter, composed of Schedule II API, and need a 0.010-inch cup depth. If one would adhere to the TSM tolerance, the cup depth would deviate at 30% from the original value. Considering this, if one would also compress an OTC tablet with a 0.070-inch cup depth, the allowable deviation would be at 4% resulting to tablets with controlled substances having more leeway than that of a regular OTC tablet.

Establishing A Limit

As new tools enter the production and now become in-process tools, tablet manufacturers should set a standard deviation limit to ensure equipment life and consistency of tablet quality. The reasonable limit would be a 15% decrease to the cup depth from the original spec of the tooling. By implementing this limit, one would be able to maintain the product within the set deviation limit and be consistent irrespective of the original cup depth.

The set limit would also allow tablet manufacturers to maintain the tools and polish these without having to worry about affecting the tooling life or service. With the in-housestandard, one would no longer worry about proper maintenance and this would lead to significant reduction of operation costs while still being able to maintain the efficiency of the tools. Aside from this, potent tablets requiring shallower cups would be more consistent and closer to their specification.