Just wanted to thank everyone for their helpful and patient input on this rather long thread. I think significant improvements were made to our original spec and the improved version has been put into use.
Kenat - eMachineShop supplies customers with a free CAD package that has a field for a single tolerance number and we are polishing the policy for how we use that number. This thread so far has made good progress to that end and the input is appreciated. Again, we are talking about drawings...
Kenat - our CAD has several things that lead to the tolerance policy but of course there are always people that don't read much of anything - not much we can do about that. But they are forced to enter some value for T and if they have no idea of what they are entering and don't care there is...
Kenat - I appreciate, understand and partly agree with most of your comments, with the possible exception of your ummm concluding remark.
Though 2.8 T is advantageous to the supplier, it's not as elegant IMO - you have to explain where the strange number comes from, on top of explaining the...
Taking recent suggestions and doing a little more polishing, how's this:
http://files.engineering.com/getfile.aspx?folder=835dc33d-1a9e-4efe-af99-48d7ae6d3339&file=gdt-policy-2.jpg
fcsuper - Thanks for your suggestions - I will update the image.
I'm treating FOS and non-FOS differently for a few reasons:
1) We want a looser all-over profile tolerance so as not to unduly constrain us as the supplier which ultimately helps keep prices down, which, of course, is what many...
Using the suggestion of FCF's and putting them in general notes, what do you guys think of the image linked below?
http://files.engineering.com/getfile.aspx?folder=81712e3a-1d87-4d3b-997c-e36e12b869e4&file=RDD.jpg...
John-Paul - It was my intention all along to "invoke" things in Y14.5. But I could use some help with the language of the policy. I didn't say our customers don't know GD&T. Some of them do, some don't. But even the ones that do often rely on our approach without problems. I don't know what you...
Pmarc - Thanks for your comments. In reply:
1) I don't know what link you refer to and I am the author. MechNorth wrote "by invoking Y14.5, you get Rule #1 which means your toleranced size controls your form as well". Since the policy invokes Y14.5 and I want size to control form and don't want...
321GO - Thanks for suggesting DIN - I don't have a copy but found some excerpts on the web - doesn't seem as elegant or well known as Y14.5.
MechNorth - I have no objection to Rule #1 and I do mention datum via best fit but I am open to alternatives such as giving the supplier (us) the option...
I think I caused some confusion with:
1) FOS are within tolerance +/- T;
I meant, and let's change that to:
1) The size of FOS are within tolerance +/- T;
MechNorth - why do you say "Without invoking GD&T (specifically Y14.5)," when the draft directly references Y14.5? And in my 29 Jul 10...
321GO - What in particular do you feel is confusing? Y14.5 does not have the policy we are developing but that does not mean we can't develop a policy for our customers who don't want (and in some cases don't have the skill) to explicitly specify GD&T. And we are using Y14.5 concepts in the...
Kenat - Once again I see an error I made - I meant a position tolerance zone of diameter 2T. And unless you have a strong objection I think this type of position is more natural and easier to grasp. Therefore (with some more polishing) we have:
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Based on a specified numeric value T (e.g...
Kenat - I now see and apologize for creating some unnecessary confusion with "+/-" in my July 25 draft. I intended the following (I also combined 1&3):
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Based on a specified numeric value T (e.g. .005") the manufactured part shall be considered in conformance if all of the following are...
Kenat - Thanks for your detailed input. You are a bit more advanced that I, so would you kindly clarify "applying the +-T as an equivalent equal bilateral surface profile tolerance (so 2T)". I intended an equal bilateral zone of T on each side which I believe is a profile tolerance of 2*T. And...
I would be interested in comments on the following policy for handling non-dimensioned (and incompletely dimensioned) CAD models:
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Based on a customer specified general +/- tolerance T (required by the eMachineShop CAD) the manufactured part shall be considered in conformance if...
fcsuper - You seem to have hit the problem home with "There is no industry standard for this. Y14.41 is useless." So we need to provide our own policy.
Drawoh - Correct - we need an acceptable policy for accept/reject of non-dimensioned features of CAD drawings our customers supply us and the...
Thanks for the many comments but let me clarify what I am looking for. Perhaps Reduced Dimension Drawings is not the right term. The reality is that many of our orders from customers ranging from experienced engineers at space agencies down to individual inventors provide NO explicit dimensions...
