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  1. #61
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    It seems people are talking past each other. We have the same problem between the machinists and the engineers.
    My friend here got me saying "hey we can make whatever you design, if it costs every last penny our company has".

    See, the deal is, if we have to adjust the model on the shop floor (and we do frequently), then that costs the company money and potential for error.

    If we have to manually adjust the posted G code (to use a different geometry offset for the finishing tool on one feature that is not modeled the same as the other features) then that costs money and potential error.

    If the print that the lathe guy works from (no CAM, he uses Mazatrol on the lathe) has a feature that interfaces with a 3D milled feature, then we can have mismatch. Happens more than I like. Well, once is more than I like.

    Before I write a book (too late?), we're all trying to make money and minimize errors. So model to the mean.

    Look at it this way: modeling to the mean doesn't hurt but modeling to extremes can.

    My two cents.
    Chris

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    Quote Originally Posted by Chris59 View Post

    If the print that the lathe guy works from (no CAM, he uses Mazatrol on the lathe) has a feature that interfaces with a 3D milled feature, then we can have mismatch. Happens more than I like. Well, once is more than I like.
    I gave your post a like, so don't take it wrong. But get used to the above happening, regardless of whether it's been modeled to your satisfaction or not. Unless you are doing all the Turning and Milling in a single, multi-tasking Machine----even then?? Sometimes.

    R

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  4. #63
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    Quote Originally Posted by Chris59 View Post
    Look at it this way: modeling to the mean doesn't hurt but modeling to extremes can.


    Chris
    There, I've made the quote of the day visible!

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    Quote Originally Posted by CarbideBob View Post
    I think a 2x4 is a great example of nominal dimension.

    As a kid I actually thought that they should be 2 x 4 inches and the stuff in my hand must be something else altogether.....
    Someone should have explained that 2x4's are 2" x 4" -- rough. Sometimes in an old house you'll find walls built with 2x4's from before they were commonly finished to be smooth. Makes you wonder why people want finished-type lumber ? Nominal is easier to divide by 2, sturdier, get a little more soundproofing, makes a nicer wall. Nominal is cool

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    Quote Originally Posted by litlerob1 View Post
    You post a link to anything that backs you up. Sorry, but your information is not correct or accurate.

    Definition of the word in context of Engineering.

    The aeronautical sense of nominal derives from engineering where the nominal value is the specified dimension and the reference point for tolerances. ... (engineering) A permissible deviation from a specified value, expressed in actual values or more often as a percentage of the nominal value.

    But even the Web consists of conflict, because the very nature of the word is relative to the environment, the conversation, the background and the teaching chain.

    R
    Teach is right.

    Here's your article

    Real versus nominal value - Wikipedia

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    Quote Originally Posted by Chris59 View Post
    It seems people are talking past each other. We have the same problem between the machinists and the engineers.
    My friend here got me saying "hey we can make whatever you design, if it costs every last penny our company has".

    See, the deal is, if we have to adjust the model on the shop floor (and we do frequently), then that costs the company money and potential for error.

    If we have to manually adjust the posted G code (to use a different geometry offset for the finishing tool on one feature that is not modeled the same as the other features) then that costs money and potential error.

    If the print that the lathe guy works from (no CAM, he uses Mazatrol on the lathe) has a feature that interfaces with a 3D milled feature, then we can have mismatch. Happens more than I like. Well, once is more than I like.

    Before I write a book (too late?), we're all trying to make money and minimize errors. So model to the mean.

    Look at it this way: modeling to the mean doesn't hurt but modeling to extremes can.

    My two cents.
    Chris
    You're spot on.
    In my experience, design/CAD jockeys
    a) don't understand the necessity of modelling to mean but are too proud to ask
    b) just don't care

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    Quote Originally Posted by Rewt View Post
    Always always always always create the model to perfect form. You can call out the tolerances in the drawing however you want (we prefer symmetric bilateral). The point is some CAM guy is going to, at some point, pull the model in and never look at the drawing. Don't laugh, I've seen it happen.

    Drawings and models are a form of communication, your goal is to communicate as clearly as humanly possible. Having someone do extra math is just not good practice.

    Seeing 5.000 -0.016/-0.032 drives me up a wall. Yes the dim is 5 nominal. Is the part going to be used nominally? No. Then write the damn thing 4.976 +/-0.008 and be done with it.
    +1 billtrillion
    Model mean
    And write the limit on the print to lessen errors/mistakes/dyslexia

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    Quote Originally Posted by Rewt View Post
    Teach is right.

    Here's your article

    Real versus nominal value - Wikipedia
    I believe that TMP and I were/are on the same page.

    From your article;

    "The distinction between real value and nominal value occurs in many fields. From a philosophical viewpoint, nominal value represents an accepted condition, which is a goal or an approximation, as opposed to the real value, which is always present."

    Which is exactly why we shouldn't be using the word across different environments.

    R

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    Rob/Seymour...please read/quote the other 90% of the article linked and not just the philosophical first two sentences. It is peppered with real examples, including both the 2x4 example and the pipe example. The normal accepted use of the word nominal is not that complicated or philosophical.

    If you really want to get philosophical on it, you are interpreting your quoted section backwards. It is stating that the nominal value is the entire range of acceptable conditions (within tolerance) because the real (target/mean) value is impossible to measure finitely.

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    Quote Originally Posted by JCByrd24 View Post
    Rob/Seymour...please read/quote the other 90% of the article linked and not just the philosophical first two sentences. It is peppered with real examples, including both the 2x4 example and the pipe example. The normal accepted use of the word nominal is not that complicated or philosophical.
    Perhaps you should re-read the article and quote THE line that contradicts what I or Rob is saying about the word "Nominal"
    Here is a hint:

    Nominal sizes may be well-standardized across an industry, or may be proprietary to one manufacturer.
    IOW, in MY shop, in MY environment and for OUR purpose, the word Nominal is used as the median or target ( let it be dimension or whatever else )
    because that is what I say it means.

    I really don't understand why is it so hard to grasp, specially when you quoted the Wiki link!

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    I don’t see what point you’re trying to make. It doesn’t say the word nominal may be standard or proprietary, it specifically says sizes. You seem to think the word can mean anything you want it to and Rob seems to think the word is too complicated to use properly in any context. Am I misunderstanding either of you?

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    Quote Originally Posted by JCByrd24 View Post
    It doesn’t say the word nominal may be standard or proprietary, it specifically says sizes. You seem to think the word can mean anything you want it to and Rob seems to think the word is too complicated to use properly in any context. Am I misunderstanding either of you?
    Line1:

    The distinction between real value and nominal value occurs in many fields. From a philosophical viewpoint, nominal value represents an accepted condition, which is a goal or an approximation, as opposed to the real value, which is always present.
    Where does it say that the word "Nominal" specifies size?
    In fact it says that it represents an accepted Condition!

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    I believe the "accepted condition" refers to things such as "All systems nominal" meaning everything's working within specification.

    YouTube

    and

    YouTube

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    We've had confusion along these lines in our shop before, and the best I can resolve it is that you can't smear engineering and machining together. Even if it's one guy doing both, they have to be considered separately, or once a second individual comes in the mix (sometimes that's just the customer) it gets really confusing really fast.

    In this case, The engineer (even for those who are not "engineers") Is the guy who decides the tolerances and dimensions. He doesn't care how the part will be made, he just knows that a .500" shaft will not fit in a .500" hole. He SHOULD know that +/-.0001" tolerances are not always necessary and can kill needless time and resources, but it's also up to him to supply clear dimensions to the machinist. Even if it's crayon'd on a napkin, it's got to have all the relevant information.

    The Machinist doesn't care what the dimensions are, he's just trying to achieve them. If there's a problem on the print, He can go back to the engineer for clarification, but it's not his responsibility to change things by himself. He tries to hit between the tolerances however they are written. If he's drilling a .500" hole, he shouldn't care how many .00005" it's off, or if a .495" hole would be "better." If it comes out between .4995", and .5005", he did his job.

    When the engineer decides to let the machinist call out tolerances = problems.
    When the machinist decides that a tolerance is too loose/tight = problems.

    Each is responsible for their own job, but they should be working together to make the company money. If they can't communicate, that's not a tolerance problem, that's a business problem.

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    Understand this as a fact, not an opinion.

    Lets say for example, we are Turning a 1" bar of 304L down to .875" +-.005". The "Target is .875" which is Nominal. The 1" bar is also Nominal. And when the Machinist pulls it off the Machine and measures it, he get .8763"(in tolerance) that is Nominal. When it goes to QC and retard inspects it and gets .8764" that is also Nominal. Every number, value, integer, digit between 0 and 9 is Nominal TO ITSELF.

    That's why using the term is stupid and self defeating, UNLESS it is a Nominal and accepted definition across the environment. It is NOT here, so quit!!!

    R

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    Quote Originally Posted by SeymourDumore View Post
    Line1:



    Where does it say that the word "Nominal" specifies size?
    In fact it says that it represents an accepted Condition!
    Your exact quote (the first time) says nominal size!!! Everything in that article talks to the fact that a nominal size has nothing to do with any type of actual size. It’s a trade size, or size as ordered, or a size by name. Then you quote a totally different line. You guys are all over the map. Learn what nominal freaking means, its not that freaking hard! You and your shop are using it wrong, by your own definition!

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    Quote Originally Posted by litlerob1 View Post
    Understand this as a fact, not an opinion.
    Lets say for example, we are Turning a 1" bar of 304L down to .875" +-.005". The "Target is .875" which is Nominal. The 1" bar is also Nominal. And when the Machinist pulls it off the Machine and measures it, he get .8763"(in tolerance) that is Nominal. When it goes to QC and retard inspects it and gets .8764" that is also Nominal. Every number, value, integer, digit between 0 and 9 is Nominal TO ITSELF.
    That's why using the term is stupid and self defeating, UNLESS it is a Nominal and accepted definition across the environment. It is NOT here, so quit!!!
    R
    That is a confusing concept. Interesting thinking.
    I do not know why people need models built to mean or middle dimensions.
    You comp everything in this world. It's not like your 1/2 inch endmill is made to or will cut .5000.
    Heck many buy inserts with a M in the third letter. +/-.005 and actually +/.0075 over the tip is fully in spec. I'm sure many are making parts closer than .010-.015 in diameter on their lathes with such.
    Show of hands, how many have ever bought an A tolerance insert and why? Crazy price tags and yes I do make them for special apps so they do exist.
    Normal people just comp at the machine, in the CAM or a combination.

    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.
    Bob

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    Quote Originally Posted by JCByrd24 View Post
    Everything in that article talks to the fact that a nominal size has nothing to do with any type of actual size.
    Oh, you have gotta be kiddin' me!
    NOTHING in that article talks to the fact that Nominal means size!
    Nominal can be anything! A simple value which does not even need to be a numerical value!
    It can be a color, material, a unit of measure or just about anything that is accepted and agreed upon.

    But since you're all hung up on the fact that "nominal" does refer to size then please tell me what is the nominal size
    of a drilled hole that is defined ( called out on the print ) as:
    .499-.497 DIA

    Now contrast the same hole being called out as:
    .500 DIA -.001/-.003

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    Quote Originally Posted by litlerob1 View Post
    Understand this as a fact, not an opinion.

    Lets say for example, we are Turning a 1" bar of 304L down to .875" +-.005". The "Target is .875" which is Nominal. The 1" bar is also Nominal. And when the Machinist pulls it off the Machine and measures it, he get .8763"(in tolerance) that is Nominal. When it goes to QC and retard inspects it and gets .8764" that is also Nominal. Every number, value, integer, digit between 0 and 9 is Nominal TO ITSELF.

    That's why using the term is stupid and self defeating, UNLESS it is a Nominal and accepted definition across the environment. It is NOT here, so quit!!!

    R
    And your opinion is way off what the rest of us know as fact. The concept of nominal is not hard. Learn it.

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    Quote Originally Posted by CarbideBob View Post
    I do not know why people need models built to mean or middle dimensions.

    Bob, read the "Quote of the Day", highlighted with big, bold red letters in post #63.

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