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  1. #21
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    Quote Originally Posted by implmex View Post
    If the student could be billed in beers...

    Hell, I'd retire on that part.

  2. #22
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    The majority of the parts I deal with, we have a general note in the title block that indicates "All diameters are concentric to a common center line within .005 T.I.R.".
    Since almost everything is round, it pretty well covers 99.9% of the stuff I design and is built. Yes, We, I, do work with the shops with the parts and they know where they can turn a part around to do the second operation of finishing the OD or ID or both and keeping the concentricity within the required tolerance. Generally, the critical OD's or ID's are all machined in the same setup without question. The only time I recall concentricity being an issue is when an operator uses too much chuck pressure or fails to use a plug on the ID of an part and wind up with egged shaped parts. Ken

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    I have two parts in an assembly with this situation. Part "A" has a deep drilled bore with a step smaller at the bottom, likely to be drilled from the other end. Part "B" is a stepped shaft that fits the bore. I put the GD&T on the print for concentricity, but we also made sure both parts are made at the same supplier and added a note saying that parts "A" and "B" must assemble and rotate freely without binding.

  4. #24
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    Quote Originally Posted by mhajicek View Post
    I have two parts in an assembly with this situation. Part "A" has a deep drilled bore with a step smaller at the bottom, likely to be drilled from the other end. Part "B" is a stepped shaft that fits the bore. I put the GD&T on the print for concentricity, but we also made sure both parts are made at the same supplier and added a note saying that parts "A" and "B" must assemble and rotate freely without binding.
    Yes! That is the best way to make assemblies IMO. I once worked with an engineer when I was prototyping engine stuff. Had some silly tolerance on one part like +.0002/-0.0 and the mating part -.0002/+0.0

    When I questioned it (was something we were trying to farm out because we did not have the capability. Well he couldn't understand why we were getting all these no-quotes (was one of each piece). So I looked at it, asked where it fit and what it did, then suggested he dimension one part +/-.001 and the other part to be a slip (or press don't remember) fit to the first one. TA-DA had the part made really easy then, and probably cheaper too.

  5. #25
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    I did 3 of the 5 years of a mechanical engineering degree, and since I already had one degree I never finished. I honestly feel the program did more harm than good for these kids. Their ignorance was astounding, and that isn't their fault. Engineers in the past worked up through the ranks, they didn't start as engineers.

    Anyway, to my point... putting an ASME or DIN standard on a print, is asking for additional trouble in my opinion. You are far better off communicating directly to the piece being made.

    I recently did a part for a Tier 1 manufacturer, the print was horrible, only a couple dimensions had tolerances. After looking at the print for awhile, I realized there was a DIN standard tucked in a note. It was an old standard from the early 80's. But what it meant was, a diameter that had a .0002" tolerance was right next to a hex that had a .010" tolerance. Since there was no callout, only a centerline, the hex could have been offset .005" to one side, and still "technically" been made to print. Would the part have worked? No idea...

    Remind your CEO that with the reworks, the details will cost twice as much after being manufactured in Mexico.

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    Quote Originally Posted by Fal Grunt View Post
    I did 3 of the 5 years of a mechanical engineering degree, and since I already had one degree I never finished. I honestly feel the program did more harm than good for these kids. Their ignorance was astounding, and that isn't their fault. Engineers in the past worked up through the ranks, they didn't start as engineers.

    Anyway, to my point... putting an ASME or DIN standard on a print, is asking for additional trouble in my opinion. You are far better off communicating directly to the piece being made.

    I recently did a part for a Tier 1 manufacturer, the print was horrible, only a couple dimensions had tolerances. After looking at the print for awhile, I realized there was a DIN standard tucked in a note. It was an old standard from the early 80's. But what it meant was, a diameter that had a .0002" tolerance was right next to a hex that had a .010" tolerance. Since there was no callout, only a centerline, the hex could have been offset .005" to one side, and still "technically" been made to print. Would the part have worked? No idea...

    Remind your CEO that with the reworks, the details will cost twice as much after being manufactured in Mexico.
    We had some dies built in Mexico many moons ago. Talk about horrible!

    Un-hardened punches/dies, shit work on everything... they were cheap though.. haha..

  7. #27
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    Ours weren’t quite that bad, but the number I heard, including original purchase price, freight, duties (etc), labor for inspection after the dies made bad parts, disassembly, rework, new details, then reassembly, tryout, all added up to double the cost.

    That doesn’t include the time setting up the die in the press, the bad parts it made, etc

  8. #28
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    To partially answer the OPs original question, IF you call out ANSI 14.5 on your drawing, and there are no other callouts for concentricity or runout, the standard has what is referred to as "Rule 3" . This states that at maximum material condition, all features must have perfect form in the absence of any other callouts.

    SO. . . . if all your diameters are at max size they must be perfectly round and no runout. As they deviate from max size, out of roundness and runout are allowable up to the perfect form envelope.

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    People will always argue what is a passable part which is why we get more and more drawing rules to the point a normal human can't know or understand them all.

    It all works best when the engineer and the people or shop making the parts communicate about function.
    But now we have computers and people don't talk to each other or bother to understand how and what the other is doing.

    Just throw it over the wall and hope for the best.
    Then when it does not fit or fails in use you can discuss this symbol or that standard forever while trying to place blame.
    I'm sure many of us have been backed into that corner. It's not productive.
    Bob

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  12. #30
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    Quote Originally Posted by CarbideBob View Post
    People will always argue what is a passable part which is why we get more and more drawing rules to the point a normal human can't know or understand them all.

    It all works best when the engineer and the people or shop making the parts communicate about function.
    But now we have computers and people don't talk to each other or bother to understand how and what the other is doing.

    Just throw it over the wall and hope for the best.
    Then when it does not fit or fails in use you can discuss this symbol or that standard forever while trying to place blame.
    I'm sure many of us have been backed into that corner. It's not productive.
    Bob
    yeah +1,

    Failure to communicate is not an excuse.

    If it's small scale why leave anything to chance down to the interpretation of an obscure hieroglyph.

    (I always tried too figure out what visual "language" the machinists I worked with understood and "Convert" accordingly in terms of refences, "form tolerances" and datums etc.).

    Also best to work with the folks that make your parts (if you can). [Captain Obvious]. ~ But not every outfit / organization permits that but presumably large outfits have made some efforts at internal standardization ? OP seems to be working locally/ smaller (maybe).

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    I didn't read all of the replies, so it may have been stated before.

    Does not a T.I.R. callout (of whatever amount deemed necessary) accomplish the requirement of the following:
    Concentricity
    Collinear axial runout
    Roundness

    Prints from some of my customers have a TIR of 0.002" (or) 0.005" maximum.
    TIR = Total Indicated Runout

    Doug.

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    Quote Originally Posted by Joe Miranda View Post
    If it's a turned part, concentricity is going to be as close as the machine spindle runs out. GD&T has not been the help to industry that the engineering community had hoped for. Notes on the drawing are usually much more meaningful than GD&T can EVER be. A note that says diameters "A,B &C" must be concentric within +/- xxx is much more helpful and meaningful.
    Until the job goes to INDIA...then you'd better have filled the drawing with every GD&T symbol you can find.

    Make up some more if you find a few sq. inches of deserted drawing area.

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  16. #33
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    Quote Originally Posted by Dan from Oakland View Post
    To partially answer the OPs original question, IF you call out ANSI 14.5 on your drawing, and there are no other callouts for concentricity or runout, the standard has what is referred to as "Rule 3" . This states that at maximum material condition, all features must have perfect form in the absence of any other callouts.

    SO. . . . if all your diameters are at max size they must be perfectly round and no runout. As they deviate from max size, out of roundness and runout are allowable up to the perfect form envelope.
    That's Rule #1, but its absolutely right. If no symbols are present aside from size, its perfect form at MMC. Create a Max Material Boundary and stay within that, while staying within your diameter/length tolerances obviously. This covers your entire form. GD&T is very clearly laid out in ASME Y14.5

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    GD&T is great if everybody in the chain fully understands it. Well, that leaves me out! IMO, concentricity is a call-out that should almost never be used. It doesn't mean what everybody thinks it means, and it's hell for QC to check.

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    Quote Originally Posted by Conrad Hoffman View Post
    GD&T is great if everybody in the chain fully understands it. Well, that leaves me out! IMO, concentricity is a call-out that should almost never be used. It doesn't mean what everybody thinks it means, and it's hell for QC to check.
    Understand where your coming from....however, how would you Gd&T a shaft with 2-3 bearing fit's like a spindle ?

  19. #36
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    My preference would be a note, but I think a GD&T runout call-out would be the place to start.


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