When a Supplier Doesn’t Understand GD&T

Several times I have heard that a designer is hesitant to use GD&T because he knows that the manufacturer will not understand it.  There are several ways to answer this dilemma:

  • Too bad; the burden is on them to learn it
  • Use traditional tolerancing even though it lacks the benefits of GD&T
  • Use a hybrid approach, and make yourself available for guidance if they have GD&T questions

Without sounding callous, the best answer is probably the first option.  Even small machine shops go through the process of becoming certified in ISO, so why shouldn’t they be fluent in GD&T?  They will be handicapped in their business by not knowing this important tolerancing system.

I don’t know if this is true or a tall tale, but one engineer at our seminar said that he once worked at a small manufacturer that, when bidding on a new job, would count the number of GD&T callouts and multiply it by a cost factor.  The thinking was that more GD&T callouts meant a more expensive product to produce! Needless to say, that is nonsense.

Of course, you may want to gently ease into the GD&T waters if you know that a supplier isn’t comfortable with it. (You might not want to throw a “zero tolerance at MMC” at them right away.)   But the bottom line is that GD&T provides maximum tolerance at efficient costs, so every manufacturer should become familiar with it to avoid extinction.

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