The second part of the tolerancing procedure uses Allocate Gap Pools. In Example of Calculate Gap Pools, you calculated the gap mean and variance pools. Now, you need to specify two sets of weights, one for each pool.

In this example, the gap mean pool is 0, so it doesn't matter how you allocate it. You decide to make up the gap mean pool 50% by reducing the mean in the pad, 30% by reducing the mean in the backing, and 20% by reducing the mean in the cover.

The gap variance pool is 0.0002839, and you decide to make it up as follows:

Choose Six Sigma > Design for Manufacturability > Allocate Gap Pools.

In Allocation weights for Gap variance pool, enter 'Var Alloc'.

Click OK.

Interpret the results

As shown in the Session window output, the long-term gap Z.Bench now equals 4.5, which is the goal. More importantly, the design now has an overall yield of ~100%, compared to the original design's overall yield of 46.91%.

Note that achieving a long-term gap Z.Bench of exactly 4.5 does not always occur with a variance pool, but it should always occur with a mean pool.

The table of adjusted means and standard deviations shows what the short-term means and standard deviations must be for each element in the assembly, in order to achieve the desired long-term performance of the assembly. These values are then used to calculate the optimal tolerances for the elements in the assembly. For more information on calculations, go to Calculations for the specification limits for Calculate Gap Pools.

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