Not a kosher callout. First of all, it seems to be one that goes back a few decades (because the datum reference is listed before the tolerance value), but the problem is mainly in the mixing of TIR with the concept of concentricity.
Concentricity by definition requires a mathematical analysis of the surface to determine "median points." It can't be checked directly via TIR.
I suspect they meant circular runout.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
By changing it to the circular runout symbol, it would be saying that "the circular runout of the designated feature may not exceed .002." This can be translated to say that the TIR at any random cross-section may be no greater than .002 (highest to lowest gage reading through one revolution).
In terms of symbology, the feature control frame would start with the symbol for circular runout (single arrow at an angle), then .002, then the letter A. If everything else on the drawing has the letter before the number, that may be maintained, but the acronym TIR is not used in geometric tolerancing.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
I like the non-rounded font. The Concentricity symbol looks kind of like a stop sign. It's kind of ironic, the part could be made like an octagon and still have good Concentricity.
mfgenggear,
Thank you for your comment, people prefer to forget the past. This seems very true in the case of concentricity a very common drawing term in the past. It is there like parallel and perpendicular on old drawings, that is probably why it is so hard to kill off, it came before symbolic GD&T. I believe, an attempt was made around the ’82 standard to remove it and it’s poor cousin symmetry, completely.
Some may have the excuse of being too young or new to all of this. I would think people who are interested in education should be more careful. Are we interested in education and truth it feels morelike quash the history stuff we don’t like and indoctriinate and brainwash.
To sit and criticize the work of people who were working “in the trenches” and "according to the law of the time" is. in my view, very narrow-minded. I prefer to point the finger at the management structure that chooses to perpetuate the old way and doesn’t value updating to modern practices, that is where the problem lies. The people using this were probably the best and brightest of the time trained by their experts in that “new fangled” GD&T. We will see how people will feel about our “you can’t do that it is not a feature of size” stuff, 50 years from now.
My copy of MIL-STD-8 (GD&T's history, before ’82 and ’73 and yes, even ‘66) says this is a very correct call out. You are diven no context here to judge it against. Isn’t it then just dependant on what standard is being referenced? Basically the TIR (total indicator reading) reference was their way of saying cylindrical zone kind of like DIA, they hadn’t thought of a symbol for that yet, I guess.
The single runout arrow used to mean total runout at that same time, if you wanted circular it was noted beneath the callout as “CIRCULAR”, then, I believe in ’66 they flipped it around and you had to write “TOTAL”, how about that for confusion. If they meant circular runout they could have just said it. I know it is what is popular now because it is easier to check, but it still doesn’t tell me is it out of round or eccentric if that is what I need to know.
The standard makes clear the version of the standard applied should be noted for just this reason, to apply modern definitions to an older drawing is the error or to pretend that history did not exist is the error.
Frank
bryjarmoc - what standard if any is called out on the print?
mfgenggear & fsincox actually make a reasonable point. If an older spec is referenced then perhaps dgallup is being a bit harsh.
However, I think I've seen vaguely similar notation on a drawing which stated "ASME Y14.5M-1994" in the title block, in this case dgallup may be a bit fairer.
Perhaps this should serve as a reminder to us that when posting questions we should state what standard is in force (if known), and when answering questions with out this info, we should ask what standard applies.
KENAT,
I don't mean anything personal to anyone. The disconnect between the “real world” or “the trenches” I see day to day and the views of the committee and here almost shocks and greatly saddens me. Am I the only one out here that is still working with the '82 standard with a general mentality level of maybe '73 or '66? I doubt it. I think it is very similar to our government and us. The standard needs to be enabling to make your job easier not a bunch of petty rules that make it harder to follow.
I know rules need a definition that was the problem with the old way, it was not consistent and no one was sure exactly what was meant. However, to have tools in a tool box and say: "wink, wink you can't use them" is not enabling and is ridiculous. I like the ISO definition of concentricity it can be applied to squares or a hex that is enabling. One of the reasons I like the ISO is because it lays out general concept and lets go, I know that scares people but if you look at history much of the blame really would have to fall on the standard itself because they changed, not the people who try to use it and keep up.
I was the one who kind of ragged on the original callout, but simply due to experience I would be surprised if the OP's callout is really taken directly from a 40-year-old print.
Almost 100% of the time, when I see concentricity on a print, it's a case of the designer thinking that the word concentric sounds good, but he doesn't understand the full ramification of the symbol. (If it's an ISO drawing the interpretation is different, it still would have nothing to do with TIR).
So I'll accept the basic premise that we shouldn't judge too harshly -- mea culpa. But now we're all dying to see what the title block says for that drawing!
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
Maybe I was too harsh if it really is a 50 year old print. However, I work for a company that has bought up a number of smaller firms. I see this kind of stuff on their drawings every day. Parts that are over constrained, under constrained, meaningless GD&T, meaningless material specs, no indication of any kind of standards, etc. etc. It is not the work of the "best & brightest of their day". It is the work of the untrained & uncaring doing not quite enough to get by. Truly frightening. But they also never did an FMEA, suitable qualification testing or any of the other engineering a responsible company would do.
John,
I mean nothing personal; I will not be too surprised if the generic title block says 1994, either. It is what the world of CAD or Mylar copying and “Just use this as a reference” has brought upon us. This is combined with a general attitude that “it is not that important anyway”. I am constantly battling with this issue of old drawings showing position callouts to no datum reference, as was also common “in the good old days”, COMPLETELY “by the book”. The management perspective as I stated above is “it was OK before”. I am jealous of you who can start all over, fresh each time. I don’t believe it is true in the "real world" so to speak, though. I believe that is why there is a large disconnect, do you not percieve it too?
I believe you supported me when I supported the use of a cone as a datum, as is now shown in the 2009 standard, I thank you for that, if you did not that is OK too. I suspect though the "caliper people” are going to be in no hurry to adopt that, fortunately I no longer have to wait for them. I was using composite position with secondary datum references before ‘94’s blessing, because I needed a way to specify that requirement even though it was not yet generally accepted or “in the book”. I had to add a note to say what I intended to each one. Someday someone will look back and say, “why did this fool go through all of this trouble to do this, it is what it means anyway”.
That is the perspective I felt needed to be made here.
One of our clients does work to the 82 standard for some projects (required by contract) as well as the 94 standard (the first note on the drawing refers to their drawing interpetation standard that in turn refers to the appropriate ASME Y14.5 standard). I do see alot of examples of parts where the tolerances etc were just copied from the reference without thinking about what is required. (I have been guilty of the myself on occasion.)
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
Bryjarmoc,
In answer to your original question, I believe it is roughly equivalent of saying: "concentric to a cylindrical zone of .002 to the datum referenced". As was stated earlier this is an very old way of doing it and I would not recommend using that current method on a new print. As to whether you want concentric at all, for your application, it will depend on the application.
I will let others explain why you should not choose it.
Frank
