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Thread: Machinists, get ready to shoot me

  1. #21
    Insider Ydna's Avatar
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    It gets tricky for the reasons you're saying, and you're correct that .850 plus-minus 0.01 could be misinterpreted as 0.015....but if you want to avoid it then just make all the callouts use three decimal places. Some drafting purist from 1995 might get angry, but the correct information would still be conveyed so who cares. Any specific dimension with a tolerance associated with it will automatically override the general tolerance information so you can make it whatever you want. The only thing is it might get confusing if you have a lot of tolerance windows all over the board, but hey at least everything is right there in plain view...

  2. #22
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    At one of my old companies, we did a CTF (critical to function) callout on the dimensions that had to be verified on every single part. That designation also bolded the dims and noted that they were subject to the toleranced provided and not the general tolerance. We had to do this for low cost manufacturers (overseas) to ensure workable quality. Ydna is far more knowledgable, but I am just sharing my experience.

  3. #23
    Insider PBSteve's Avatar
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    Great, thanks guys.

    It's kind of strange when I think about it. If your tolerance is 0.01", the measurement uncertainty can contribute an additional 50% beyond the stated tolerance. If your tolerance is 0.05", the measurement uncertainty can only contribute an additional 10% to the tolerance. And that happens with any positional numeral system, regardless of what base you choose - but given a specific number, your choice of base affects how much measurement uncertainty will contribute.

    Seems like a bug without a feature.
    Afflict the comfortable and comfort the afflicted
    I work for the company building the Paragon...once we figure out a name

  4. #24
    Quote Originally Posted by PBSteve View Post
    Seems like a bug without a feature.
    pretty much sums up drafting.

    many many many ways to get it wrong, really only one or two ways to get it right.
    social conservatism: the mortal fear that someone, somewhere, might be having fun.

  5. #25
    Insider PBSteve's Avatar
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    Yeah, I mean I'm pretty frustrated with all of this.

    For example I don't really care about most static o-ring glands. Crush the ring, make it seal, done. Dynamic rings are critical. Some glands have critical positions, others can be +- .05 for all I care. But then there's two spots for general tolerances, and like Andy mentioned on more complex parts if you actually include all that information on a 2D print you end up with tolerance windows all over your print and everything's there, but nothing's clear.

    There's just so much information I don't see why we're not building it into the CAD model and ditching 2D prints altogether. Point, click, boom all the dimensions and tolerances for that specific feature are right there.
    Afflict the comfortable and comfort the afflicted
    I work for the company building the Paragon...once we figure out a name

  6. #26
    right? 3d prints for sure.
    social conservatism: the mortal fear that someone, somewhere, might be having fun.

  7. #27
    Insider Ydna's Avatar
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    I think it's just aversion to change. People don't think with electronics, they still think about physically printing off big dumb sheets and carrying them around. It's the lowest common denominator. It likely also makes things easy for legal issues, being as it's a legal document and all.

    But then again autodesk could come out with something like that next year, but it would be essentially worthless for most people...unless you update to their 2019 suite and happily pay $200/month for the subscription service. And have it not work the first year (lol). I'm a huge autodesk fan but even I refuse to ditch my perpetual license...

  8. #28
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    Many big companies are doing CAD files only. As long as you have a proper PLM suite like teamcenter then it's electronically documented. My old company integrated that into SAP to essentially automate the route sheet process and it added standard view visualization and some dimensions to the .pdf traveler. Not sure how they did all that, but it worked wonders for forecasting shop load. The manufacturing engineering group got the 3d file and did the machine programming and could provide cost information before anyone in the machine shop saw it.

  9. #29
    CAD only is tough for communicating tolerances though. i know it sometimes is possible, but sometimes its also not.
    social conservatism: the mortal fear that someone, somewhere, might be having fun.

  10. #30
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    I didn't work in the manufacturing engineering group, but they had some big book of standards that they went off. Not sure if that was internal process or some mil-std/ spec. Before I went to work for the big company, I worked for a smaller company that was awarded manufacturing of some of the big company's parts. I seem to recall them sending something like a multi-layer autocad print where the layer indicated tolerances or something. I know they never sent us a proper print. We had to turn around and model the parts in 3d so we could send the parts to the CAM programmer who checked our model against the original file. It wasn't efficient at all.

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