Profile and parallelism call out on flat surface
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    Default Profile and parallelism call out on flat surface

    How do I interpret the following call out for a surface that is parallel to the datum?

    parallel to datum A .003 with an additional .002 profile call out.
    Datum A is defined by .004 profile call out.

    Wouldn't the .002 profile call out negate the .003 parallelism?

    Does the tolerance of the datum come into play at all?


    I Don't think I have seen a call out this way before, if I have the tolerance has been big enough I haven't had to take notice of it.

    Thanks guys

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    Can you post an image of the GDnT? Sounds goofy but can't really say without more detail.

    I've seen a LOT of bogus callouts.

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    Ask your customer.

    They're the one who ultimately determines whether or not your product meets spec.

    - Leigh

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    This is the call out for two parallel surfaces.

    Sent from my SM-J337V using Tapatalk

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    You are allowed .003 both surfaces simultaneously parallel to A

    You are allowed .002 profile both surfaces without reference to any datum. Think of as a flatness spec both surfaces simultaneously.

    .004 profile on your datum A likely could simply be considered a flatness spec. .004 magnitude could potentially cause you trouble meeting the other two specs. Rocking datum. Are there A datum targets?

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    Has to be parallel within .003 of datum A, but the irregularity or waves in the surface cannot exceed .002

    They are just using the profile tolerance as a refinement of the parallel callout. Its a volume between two surfaces tolerance, with two hypothetical boundaries, can be on an angle of .003 but the peaks and valleys of the surface cannot exceed .002

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    Quote Originally Posted by yoke View Post
    This is the call out for two parallel surfaces.

    Sent from my SM-J337V using Tapatalk
    Dumb callout. Parallelism is a tolerance of form. So those surfaces could be anywhere within the size tolerance limits. Profile can be used to locate a feature, but not without datums. So the profile is nothing more than a refinement of the parallelism. I would treat it as a flatness.

    I think the prevalence of CNC machines and 3d cad software has given rise to engineers who no longer understand or feel they need to know GD&T or even basic drafting. I think they are also confused about reasonable tolerances, understanding what they really need, flexibility of parts, finish thickness etc etc

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    Quote Originally Posted by AdamC View Post
    I think the prevalence of CNC machines and 3d cad software has given rise to engineers who no longer understand or feel they need to know GD&T or even basic drafting. I think they are also confused about reasonable tolerances, understanding what they really need, flexibility of parts, finish thickness etc etc
    The worst I’ve seen was a fuel cell compression plate, roughly 20” lo g dog bone shaped with 3d surfaced ports. Pretty much the only tolerances on the part were various profile tolerance GDT callouts and nary a dimension to be seen.

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    Quote Originally Posted by AdamC View Post
    Dumb callout. Parallelism is a tolerance of form. So those surfaces could be anywhere within the size tolerance limits. Profile can be used to locate a feature, but not without datums. So the profile is nothing more than a refinement of the parallelism. I would treat it as a flatness.

    I think the prevalence of CNC machines and 3d cad software has given rise to engineers who no longer understand or feel they need to know GD&T or even basic drafting. I think they are also confused about reasonable tolerances, understanding what they really need, flexibility of parts, finish thickness etc etc
    Yeah, I thought the profile should have a datum call out to mean anything. There is no feature to feature size on the drawings.

    This is an experimental-in-nature part so if they get the results they want they will relax the drawing to whatever we are able to make.


    Thanks everyone for your feedback.

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    Quote Originally Posted by AdamC View Post
    Dumb callout. Parallelism is a tolerance of form. So those surfaces could be anywhere within the size tolerance limits. Profile can be used to locate a feature, but not without datums. So the profile is nothing more than a refinement of the parallelism. I would treat it as a flatness.

    I think the prevalence of CNC machines and 3d cad software has given rise to engineers who no longer understand or feel they need to know GD&T or even basic drafting. I think they are also confused about reasonable tolerances, understanding what they really need, flexibility of parts, finish thickness etc etc
    Yes and yes!

    A few years back I worked with some really smart engineers (no sarcasm intended), but they could not understand why a 1/8" rad in a pocket 2" deep was a bad idea.

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    If it's profile to datum A, that is correct. Simple profile (to itself, basically), no.

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    Quote Originally Posted by Kai Kendall View Post
    If it's profile to datum A, that is correct. Simple profile (to itself, basically), no.
    My company thinks profile with no datum means the surface must best fit match the drawing/model within the tolerance specified, but the surface can be anywhere.

    We use it where there is no clear or useful datums. We don’t build cars but imagine a surface profile on a car windshield.


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