Tolerance interpretation

[Bill Ryan - 2007]

I had no idea where to ask this question so I stuck it here.

We make a few parts which, on the part print, have a "General Note" covering unspecified linear tolerance as follows:
Basic tolerance up to 25.4 mm = +/-0.25.
Additional tolerance for each 25.4 over = +/-0.025
We have always taken that as meaning the additional 0.025 gets added at 25.5 mm, 50.9 mm, etc. I am now "arguing" with one of my NONAUTOMOTIVE customers who says the additional 0.025 doesn't get "added" until 50.8, 76.2, etc.

I'd sure like to hear what some of you feel (or know) is the "correct" interpretation.

Thank you in advance,
Bill

 

[Sam]

"Additional tolerance for each 25.4 over = +/-0.025"
I interpret that to mean 0.025 for each 25.4 over the base measurement. So I agree with your customer.

 

[Mike S.]

Sorry, Bill, my personal interpretation agrees with your customer's interpretation. It is not the clearest way in the world to state a tolerance, for sure (an example would have been very appropriate IMO), but that is how I see it. Sorry.

 

[Bill Ryan - 2007]

Thanks for the reply, Sam and Mike - but.....

My issue stems from the fact that my customer is "allowing" a total "movement of the feature" of 0.5 UP TO a distance of 25.4. He is also allowing that as the distance increases, there is "potentially" more movement. Why doesn't the customer think there would be any increase in movement potential from 25.4 to 50.7? (By the way, this customer got frustrated by that question because he couldn't answer it satisfactorally (we could use a spell checker) and ended up giving me the "Do it my way!!!" response - which just adds to my frustration).

I agree, it's a pretty poor way to state a tolerance.

Bill

 

[Mike S.]

Your frustration and your logic is understood, but I think you're stuck based on what the customer said. Part of his logic (playing Devil's advocate here) is that you would get the same +/- .25 tolerance on a 5 or 10mm part as you do on a 25mm part, so the tolerance is not linearly applied there, either. I ASSUME that during contract review you thought you understood the tolerance and there was NO question in your mind or else you would have asked for an interpretation/clarification prior to quoting. I think this is just one of those live and learn situations we ALL face from time-to-time.

 

[Sam]

Bill,
As I see it based on the comments;

0 to 50.8 +/- 0.25
50.8 to 101.6 = +/-0.275
101.6 to 152.4 = +/- 0.300