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ISO 2768 or one size fits all general tolerance note?

Punkinhead

Cast Iron
Joined
Feb 13, 2010
Location
IN, USA
We're switching to metric for all drawings. We design one off machines, so no production runs or large quantities. 6061 or al jig plate are our most common materials and pretty much every detail we design will be smaller than 400mm and most are below 100mm. All machining is done by outside suppliers. We've always used the number of digits after the decimal for default tolerancing of inch drawings but with metric we'll drop trailing zeroes. So what would you prefer to see as a general tolerance note in the title block for machined parts? Which would you rather see, "Unspecified tolerances follow ISO 2768-fH" or across the board tolerances like "Unspecified tolerances +/- 0.13 mm, +/- 0.25 degrees for angles"? The latter ends up being tighter than ISO 2768 as parts grow but keeps the machinist from having to reference a separate document.

Thoughts?
 
Personally, even though I'm in metricland, ISO2768 is a pain in the arse.

We have exactly two customers that reference it, it's annoying to have to look it up, nobody else here knows what it means so I have to constantly remind them. It's pointless and annoying.
 
Personally, even though I'm in metricland, ISO2768 is a pain in the arse.

We have exactly two customers that reference it, it's annoying to have to look it up, nobody else here knows what it means so I have to constantly remind them. It's pointless and annoying.

Would you rather have everybody use his own system? If they are to stupid to go to Google and print out a copy - they should not be in business.
Smart people will make it part of a print.
 
I don't see the benefit of it compared to stating general tolerances in the title block. Cross referencing takes time, even if it's a small amount of time.

If everybody (or most) uses ISO 2768 than the Machinist,Tool and Die Maker, Model Makes etc. will get to know the system - even without looking at the little box on the print.
I worked on both sides of the Atlantic. A big problem in the US was that you always had to look at each print to find out what kind of tolerances were required for the job. Best thing to do was to write the decimal tolerance next to the dimension given on the print. This was not required in Countries using DIN/ISO 2768. After a while you did not even look for the little box on the print. You just knew it was 2768. Any deviation from 2768, like if a dimension required a closer tol., was noted on the print. Otherwise DIN/ISO 286 ruled for Fits and Tolerances. It was clean cut. No room for interpretation and argumentation with somebody using his own system.
Btw: You can always use:"Unless otherwise specified tol. are as per DIN/ISO 2768".
 
If everybody (or most) uses ISO 2768 than the Machinist,Tool and Die Maker, Model Makes etc. will get to know the system - even without looking at the little box on the print.
I worked on both sides of the Atlantic. A big problem in the US was that you always had to look at each print to find out what kind of tolerances were required for the job. Best thing to do was to write the decimal tolerance next to the dimension given on the print. This was not required in Countries using DIN/ISO 2768. After a while you did not even look for the little box on the print. You just knew it was 2768. Any deviation from 2768, like if a dimension required a closer tol., was noted on the print. Otherwise DIN/ISO 286 ruled for Fits and Tolerances. It was clean cut. No room for interpretation and argumentation with somebody using his own system.
Btw: You can always use:"Unless otherwise specified tol. are as per DIN/ISO 2768".

I understand your argument, I do.

I am talking from a practical/pragmatic perspective. We are a UK company, we have many customers, most of them European. Like I said before, I can think of exactly two that have adopted ISO2768 in their drafting standard.

With that kind of adoption, it is clear that this is not a popular standard. There are reasons why I am sure, and I suspect that the reason is that it is just too low resolution to be useful in many/most cases. Many of our customers require general tolerances tighter than -fH. Scaling by length is not always functional. Etc.

By FAR the most common tolerancing method used by our customers is nominal +/- and general tolerances UOS in the title block. Some use limits and general UOS, some use ISO fits and general UOS. Looking at the title block is not difficult.
 
The customer is king. You can always specify DIN/ISO 2768-f and add "Unless otherwise specified". That way you can cut down the tolerance in some places in any way you desire as required for your design. Not a big deal.
 
We just received drawings with almost no dimensions on them and the reference to ISO 2768-M. The drawings only had the tight tolerance dimensions, unilateral they were. I asked if the model dimensions were nominal and they said most dimensions were and I explained that it was too risky for us to work that way to send a dimensioned drawing and that I don't even like to make something once so I certainly don't like to make it over again. I'm glad I'm almost retired and will only make my products and things I design.
 








 
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