Drawing Tolerances and the Manufacturing Impact

Emergency Egress SearDimensional tolerances specify allowed variability around nominal dimensions.  In general, as tolerances become smaller manufacturing costs become greater.   This isn’t always the case, but it is generally true (we’ll cover exceptions in a future blog entry).

The approach used by most organizations for assigning tolerances often offers improvement opportunities in the areas of fit, performance improvement, and cost reduction.   It makes sense to consider tolerance modifications (and in particular, tolerance relaxations) where we can do so for all of the above reasons and more.  The photo on the right, for example, shows a product that was poorly toleranced and ultimately resulted in the failure of an aircraft emergency egress system.   We’ll tell you more about it in a subsequent blog entry.

If you’re wondering if any of the above might be applicable to your design and manufacturing organization, we’d like to suggest the following questions:

  • How do we assign tolerances?
  • Do we or our suppliers have any recurring rejections we suspect are induced by needlessly-stringent tolerances?
  • Are there any areas where we or our suppliers are taking extreme measures to hold tight tolerances?
  • Have we ever experienced failures with otherwise conforming equipment?
  • Do we require drawing changes to relax the tolerance whenever we disposition nonconforming parts “use as is?”

Future Blog Entries

We’ll have a series of articles in the next several weeks addressing the pitfalls in how most organizations assign tolerances, how we can approach relaxing tolerances, how tighter tolerances can sometimes actually lower cost, the need for appropriately-targeted tolerance analysis, and how statistical process control implementation can allow increasing tolerances.

Keep an eye on the ManufacturingTraining blog for important and informative updates in each of these areas!

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