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I reread ISO 2768-1 & -2 last night and it specifically says: "general tolerances" so I am not sure it negates stated drawing tolerances at all, do you know that? Those are the ones (according to this philosophy) we supposedly care about.Īs is obvious from my first post, we make mistakes all the time, I make them every day. Iit seems you have been dealing with this subject for a while. What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"? RE: A different perspective on ISO 2768 KENAT (Mechanical) 17 Jun 09 12:07 Have you reminded yourself of FAQ731-376: Forum Policies recently, or taken a look at posting policies: over in Drafting Standards, GD&T & Tolerance Analysis. I've posted in depth my own battles with a vendor using this standard and what they claimed it meant on tolerance stacks etc. Also, is the information up to date, or can modern CNC machines typically hold much tighter without significant cost increase? but I'd have serious reservations over invoking it directly. ISO 2768 may be a usefull guide for what tolerances can typically be held for a different size and grade of shop etc. However, to have it as the default setting that any discrepancies have to be verified to not to be OK seems potentially problematic. In practice I realize that under some circumstances it is desirable to accept parts that don't quite meet drawing requirements, typically due to cost or schedule pressure.
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One important function of a drawing (or equivalent MBD) is to set a legal definition of what you will or wont accept.īy having that disclaimer they are basically nullifying that concept. Thanks, I look forward to discussing it with you and learning more about it. I believe both ANSI and ISO standard are works in progress and not final statements, they evolve.ĭo you accept the concept that natural/default tolerances may need to grow as parts/features get bigger? I think it is more realistic after some 30 years of experience. I only see the good old (2) place +/-.03 and (3) place +/-.010 that is our general tolerance. We generally don't put extraordinary large tolerances on our prints either. Then this final statement is basically saying a part may not be bad if it is in one of these areas, the general toleranced areas, by that measure it may be true. The standard basically says their intent at general tolerances is to not to specify extra large tolerances manufacturing theoretically doesn't need. Personally, I think they are just being realistic. I have seen some comments here concerning ISO 27 and it's disclaimer at the end.