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Re: Profile of Surface interpretation
Re: Profile of Surface interpretation -- Art H	Post Reply	Top of thread	Forum

Posted by: Kelly_Bramble ® 04/05/2006, 10:59:18 Author Profile eMail author Edit

Without specified datums, the profile of surface tolerance zones are equaly disposed about the true profile (as given on the drawing). However, the tolerance zones are free to move as a system, left, right up or down relative to the true surface profile. I think you both are right..

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Re: Profile of Surface interpretation
Re: Re: Profile of Surface interpretation -- Kelly_Bramble	Post Reply	Top of thread	Forum

Posted by: traingdt ® 04/10/2006, 19:37:43 Author Profile eMail author Edit

For the bilateral vs. unlateral idea, you can think of it this way: the profile is indeed equally disposed around the radius of curvature, but the center of that radius may float, since no datums are mentioned. Without datums, profile only controls form, not location or orientation. So as Kelly said, you're both right in a sense. John-Paul Belanger

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Re: Profile of Surface interpretation
Re: Re: Profile of Surface interpretation -- traingdt	Post Reply	Top of thread	Forum

Posted by: traingdt ® 04/10/2006, 19:43:11 Author Profile eMail author Edit

I forgot to mention something in the Y14.5 standard that may help you. See Fig. 6-18. There we see a unilateral profile as far as form (shape) goes, but the location to datum A is bilateral around 40 mm. I guess that's the opposite of your situation, but hopefully it helps illustrate the different aspects of profile. John-Paul Belanger

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Re: Profile of Surface interpretation
Re: Re: Profile of Surface interpretation -- Kelly_Bramble	Post Reply	Top of thread	Forum

Posted by: Art H ® 04/05/2006, 14:02:53 Author Profile eMail author Edit

Thanks for the reply Kelly. By saying "the tolerance zones are free to move as a system, left, right up or down relative to the true surface profile." you are telling me that no matter where the location of the surface is the tolerance zone will move "as a system" with it, maintaining an bilateral and equally disposed tolerance zone at that location. Am I correct in understanding your response? Reason being is the vendor is arbitrarily moving the tolerance from a bilateral and equally disposed tolerance zone to a unilateral tolerance zone to suit his ability to produce the part. This will essentially double my tolerance zone from a .001" to a .002" tolerance zone for example. Is this a common practice when dealing with this form control?

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Re: Profile of Surface interpretation
Re: Re: Profile of Surface interpretation -- Art H	Post Reply	Top of thread	Forum

Posted by: Art H ® 04/10/2006, 15:05:29 Author Profile eMail author Edit

Thanks for the help last week Kelly. It's good to hear other interpretations. Is there documentation that supports this interpretation? All I have here is ASME Y14.5M-1994 (reaffirmed 1999)and it does not agree with this interpretation. If I am to use this interpretation or at least agree to it I would like to have documentation to support it. Again thanks for your help. Art

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Re: Profile of Surface interpretation
Re: Re: Profile of Surface interpretation -- Art H	Post Reply	Top of thread	Forum

Posted by: Kelly_Bramble ® 04/10/2006, 19:49:14 Author Profile eMail author Edit

First, to ensure we are on the same page, I suggest you attach a picture to this forum of the specific example/application you are reffering to. I don't know if you have a copy of my book "Geometric Boundaries" /geometric_boundaries.htm, however if you do, look on pages 8.9 and 8.10 for application specific examples. Within ASME Y14.5M - 94, see 6.5.6.1, and accomplying figure 6-20 for a example of a Profile of Surface tolerance specification which does not reference a datum. A specific example of a Profile of a Surface tolerance, which is established Bi-lateral (relative to the drawing graphics), and allowed to float as a system, is at 6.5.9.1.1, and accompanying figure 6.25. This is an example of composite profile tolerance, where the tolerance boundary given within the lower horizontal frame of the feature control frame is allowed to float as a system - up, down, left and right. This tolerance boundary must allways fall within the tolerance boundaries defined by the upper horizontal frame of the feature control frame, as well, as be perpedicular to datum A. Esplained differently. you have a outer and inner tolerance boundary established bi-lateral relative to the drawing graphics, which are best-fit to the manufactured surface. This tolerance zone is oriented perpendicular to datum A, and must always fall within the static tolerance boundaries defined by the upper horizontal frame.

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Re: Profile of Surface interpretation
Re: Re: Profile of Surface interpretation -- Art H	Post Reply	Top of thread	Forum

Posted by: Kelly_Bramble ® 04/05/2006, 14:32:36 Author Profile eMail author Edit

Art, the tolerance zones are defined initially as being equally disposed about the true profile. Datum references specify a relationship relative to the defined features. Since there are not any datums, then the tolerance boundaries are not bound in terms of orientation or location/distance relative to a datum / datum reference frame. So, yes after they establish the inner and outer tolerance boundaries, then they are free to move the tolerance boundaries around for a "best fit" with respect to the surface feature. The only way to lock down the location of the profile of surface specification, is to relate the tolerance to a datum or datum reference frame. BTW, the tolerance zones may rotate, as well, as move left, right, up, and down. Modified by Kelly_Bramble at Wed, Apr 05, 2006, 17:54:27

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