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    Quote Originally Posted by SeymourDumore View Post
    Oh, you have gotta be kiddin' me!
    NOTHING in that article talks to the fact that Nominal means size!
    Your original quote from the article literally says nominal size. The majority of the things in the article are talking about the size of them. None of them talk about color. Stop trolling. And in your example they are all 1/2” nominal!

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    Quote Originally Posted by SeymourDumore View Post
    Bob, read the "Quote of the Day", highlighted with big, bold red letters in post #63.
    And it is so wrong IMO on one sided.
    If you ran the old boards or the new CAD for me and tried this ....... Call Marvin here in Michigan.
    There are standards that go way back into paper.

    I do hate one sided tolerances as the question is always to hug the side or go for mid.
    If you have size control at 10-20% of the entire range (which I would hope all can) what is a better part? What should be the target?
    Let's say that you know you can do +/- .001 all day long and are very sure of that and have all the stupid SPC and CP bullstuff to back it up.
    The print is 3.000 +0.000/-0.010, so you have miles to play and ship good parts. Where do you run and why?
    Should the person making the model make this decision for me?
    Bob

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    Quote Originally Posted by CarbideBob View Post
    I would expect a bearing bore or shaft for a bearing to be modeled at the quote "nominal or basic" and handle the one sided manufacturing offset needed on my side when making.
    I don't need weird numbers that make you wonder WTF about the model and if the import scaling is bad.
    Ja, I think this is an area where blueprints convey the intent more clearly than models.

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    Quote Originally Posted by JCByrd24 View Post
    And in your example they are all 1/2” nominal!
    And how did you figure that?

    Would you use the same logic when you see a .3145-.3130 callout?

    Look, you're stuck in your own world and your own definition of it . That is all fine, and you're welcome to it.

    Nonetheless, the article ( initial snippet notwithstanding ) does not refer to size, rather value. Period, The End!

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    Quote Originally Posted by CarbideBob View Post

    I do hate one sided tolerances as the question is always to hug the side or go for mid.
    I don't have that problem.
    If the customer is someone I know, I may ask if they want me to hold a closer tolerance than what is called for.
    Otherwise, I just shoot middle, stay consistent and call it a day.

    Nonetheless, when MY shop drawing is on the machine, nominal means middle with a symmetrical plus/minus and the guys better fucking hold to it
    regardless of what the original B/P says.

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    Quote Originally Posted by SeymourDumore View Post
    .....
    Nonetheless, when MY shop drawing is on the machine, nominal means middle with a symmetrical plus/minus and the guys better fucking hold to it
    regardless of what the original B/P says.
    I think this is the safe rule but often I'll see some think they should bias it to one side.
    Myself, middle and no worries about ever touching that edge.

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    Quote Originally Posted by EmanuelGoldstein View Post
    Ja, I think this is an area where blueprints convey the intent more clearly than models.

    True, they do.
    BUT!!!

    Nowadays you're expected to quote and work from a solid model instead of a B/P.

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    Quote Originally Posted by CarbideBob View Post
    There are standards that go way back into paper.

    The print is 3.000 +0.000/-0.010, so you have miles to play and ship good parts. Where do you run and why?
    Should the person making the model make this decision for me?
    Bob
    LOL, I looked at that & thought it looked like an edge break on a SAE heavy blueprint… In that case 1 rev with a file or a short bump with a 45 tool gets it done.

    I can only say what I did when I did generate drawings & details. I fixed the desired size & called out the plus/minus (in CAD too). When I really did fix a number like 3.00” +0/-.010 was if the detail didn’t have anything it mated to, or close to it (like between bearing diameters), and called it nominal if asked because usually we worked to everyday size fractions here in the US. Being able to scale (or caliper) a near meaningless feature is wonderful and speedy.

    Quote Originally Posted by SeymourDumore View Post
    True, they do.
    BUT!!!

    Nowadays you're expected to quote and work from a solid model instead of a B/P.
    Not sure what to make of that^. And pretty sure if something goes pear shaped & you don't have a paper record (detail) your insurance is worthless...

    Now to the semantics, there are times basic and nominal get folks shorts in a bunch. A “basic circle” (B.C.) on a detail is a description, it has no size, no tolerance. It’s a PERFECT circle, I’ve never made one and will never know anyone that has. All the other crap called out on the detail regarding the basic circle we have done. Patterns on a specified angle of rotation, concentricity, sizes, ovality, all of it. Nominal is much the same.

    Good luck,
    Matt

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    Ohhh great!!! Now we can discuss the theory of "perfect circles" thanks Matt.

    Just kidding please....R

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    Quote Originally Posted by matt_maguire View Post

    nowadays you're expected to quote and work from a solid model instead of a b/p.
    not sure what to make of that^. And pretty sure if something goes pear shaped & you don't have a paper record (detail) your insurance is worthless...
    Matt

    How'bout getting an RFQ for a part with a skeleton of a blueprint outlining ONLY the critical dimensions and tolerances of said part, AND a fully developed solid model of the said part.

    BUT then...

    The RFQ requires that critical dimensions and tolerances are as-stated on the supplied B/P, UOS all dimensions to be "queried" from the solid model as-supplied.

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    Quote Originally Posted by SeymourDumore View Post
    True, they do.
    BUT!!!

    Nowadays you're expected to quote and work from a solid model instead of a B/P.
    Depends on your industry. Last place I worked the print (paper) was the bible and solid was "reference only" .... which is why I state solid being modeled to exactly the mean is kind of a moot point.

    Now where I work the solid model is a 'nicety' but I always refer back to the print. If there is a discrepancy, I go ask someone.

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    Quote Originally Posted by CarbideBob View Post

    The print is 3.000 +0.000/-0.010, so you have miles to play and ship good parts. Where do you run and why?
    Should the person making the model make this decision for me?
    Bob
    We've had the discussion many times here.
    The "designer" side say the drafty wanted 3.000 so aim for that.
    The "bitmakers" side say that tolerances are there to be used, so aim for mid.

    Tolerances are there to be used - don't scrap off acceptable parts because you're not near top or middle etc.
    Half a thou up from bottom is still in!

    Some Caddys i've spoken to say they model on min for FEA (strength) testing.
    Others say they model on top/nominal for weight analysis.
    All of these that i spoke with didn't understand or know why it was important to model on nominal from a manufacturing side.

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    Quote Originally Posted by barbter View Post
    We've had the discussion many times here.
    The "designer" side say the drafty wanted 3.000 so aim for that.
    The "bitmakers" side say that tolerances are there to be used, so aim for mid.

    Tolerances are there to be used - don't scrap off acceptable parts because you're not near top or middle etc.
    Half a thou up from bottom is still in!

    Some Caddys i've spoken to say they model on min for FEA (strength) testing.
    Others say they model on top/nominal for weight analysis.

    All of these that i spoke with didn't understand or know why it was important to model on nominal from a manufacturing side.

    Good points! Not every solid model we (machinist/programmer) get is specifically made to machine from. I used to work at a place where I think the primary purpose for solids was FEA and such. I had to use the print to make a good part.... (including ISO limits and fits whether you agree with them or not)

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    Quote Originally Posted by SeymourDumore View Post
    And how did you figure that?

    Would you use the same logic when you see a .3145-.3130 callout?

    Look, you're stuck in your own world and your own definition of it . That is all fine, and you're welcome to it.

    Nonetheless, the article ( initial snippet notwithstanding ) does not refer to size, rather value. Period, The End!
    Real versus nominal value - Wikipedia

    Here's the link for the third time. The word size appears 25 times on the page and you're saying it doesn't refer to size....I don't think it's me who's stuck in my own world.

    Regarding your example, I didn't figure anything to come up with 1/2" nominal, and that's the point of anything "nominal", it shouldn't be used for figuring anything because it's not a precise value. A 12V battery rarely measures 12.0 volts. But it's still widely known as a 12V battery. That's nominal. So for your second example of .3145-.3130 (should be .3130-.3145) I wouldn't apply any logic because it doesn't matter what the nominal size is when you've got the limits right there in front of you. I suppose if that's a pin I was making might want to know what size stock to start from and a little math tells me it's really close to 8mm, so maybe I'd order 8mm nominal rod. I'm not calling up McMaster and ordering "7.9mm-8.1mm" rod. (I also realize if that's the tolerance of the 8mm rod it likely isn't what I should actually order for that part).
    Last edited by JCByrd24; 12-18-2019 at 12:52 PM.

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    The OP wrote in his first post: "I do not know any CAM software, how it works or how much work these different cases put on the machinist/programmer. ------So that is essentially my question, what makes it easier on others? ------I know if someone is measuring it is easier to see limit dimensions as that is the output on the caliper without any math."
    (I don't know how to bold or underline without jumping through hoops in another program).

    See, he's asking. A reasonable and admirable thing. What makes it easier on others?
    Many here as well as myself have put forward examples about how modeling to extremes or even out of tolerance (the OPs first example) is bad for CAM manufacturing. Seems like many others here don't care.

    Why? Is there a REASON why it's BETTER to model to extremes or out of tolerance? The FEA reason is possible. Or tolerance stackup.
    However, SolidWorks does this if you build the tolerance into the model and not just the print!

    So, please, someone please help me. When is it BETTER? We've given many reasons why it's worse.

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    Quote Originally Posted by Chris59 View Post

    So, please, someone please help me. When is it BETTER? We've given many reasons why it's worse.
    It is only "better" if it suits the CAD man (FEA etc).
    It is NEVER better for bitmaking.

    Here's another way of looking at it - plating allowances on threads:-
    What's clearer, a drawing which says (for example)
    7/16 -20 UNF 2B
    and a note in the drawing border saying "Nickel plate to Blah Blah Blah"

    Or...
    7/16-20 UNF 2B
    Pre-plate Effective Dia = .xxx/.xxx Dia (where .xxx are the detailed max and min sizes to make to)

    What's going to produce less scrap?
    What's easier for the guys to make, time and time again for the length of the product life?

    You will NEVER beat detailing the sizes you want on a print and it's lazy and bad practice to do anything otherwise IMHO.

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    Quote Originally Posted by barbter View Post
    It is only "better" if it suits the CAD man (FEA etc).
    It is NEVER better for bitmaking.

    You will NEVER beat detailing the sizes you want on a print and it's lazy and bad practice to do anything otherwise IMHO.
    I think we agree 99%. I just want to make sure we are on the same page. Threads and plating are a problem we have encountered many times and I/we don't have a good answer. It's a case by case thing.

    To be clear though, I also want the print detailed.

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    Quote Originally Posted by Chris59 View Post
    The OP wrote in his first post: "I do not know any CAM software, how it works or how much work these different cases put on the machinist/programmer. ------So that is essentially my question, what makes it easier on others? ------I know if someone is measuring it is easier to see limit dimensions as that is the output on the caliper without any math."
    (I don't know how to bold or underline without jumping through hoops in another program).

    See, he's asking. A reasonable and admirable thing. What makes it easier on others?
    Many here as well as myself have put forward examples about how modeling to extremes or even out of tolerance (the OPs first example) is bad for CAM manufacturing. Seems like many others here don't care.

    Why? Is there a REASON why it's BETTER to model to extremes or out of tolerance? The FEA reason is possible. Or tolerance stackup.
    However, SolidWorks does this if you build the tolerance into the model and not just the print!

    So, please, someone please help me. When is it BETTER? We've given many reasons why it's worse.
    Semi-educated guess here. Modeling to the low limits and testing FEA for critical features so you know they work at the low end (mass, rigidity, bending, etc). Modeling to the high end for weight, mass, interference, etc...

    In a perfect world, the engineer/cad guy would make the model back to mean before passing off for manufacturing, but we all know how that works.

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    Quote Originally Posted by Chris59 View Post
    So, please, someone please help me. When is it BETTER? We've given many reasons why it's worse.
    It's better if you write articles for a magazine.

    It's worser if you have to make parts.

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    I just realized work has a copy of ASME Y14.5 2009 Dimensioning and Tolerancing, some further definition from that document:

    1.3.56 Size, nominal: the designation used for purposes of general identification.

    1.6 TYPES OF DIMENSIONING
    Decimal dimensioning shall be used on drawings except where certain commercial commodities are identified by standardized nominal size designations, such
    as pipe and lumber sizes.


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