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True position with a diameter of 0?
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Dimensioning & Tolerancing GD&T Forum
Posted by: billtheenemy

11/23/2010, 10:42:46

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Hi,

I have a question about GD&T. The first line of the tolerancing block is clear enough, but what on earth does the second line mean? (please see attached .jpeg)

Thanks,
Bill


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: True position with a diameter of 0?
: True position with a diameter of 0? -- billtheenemy
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Dimensioning & Tolerancing GD&T Forum
Posted by: Kelly Bramble

11/23/2010, 10:51:40

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This is called a "Composite Feature Control Frame".

The upper horizontal frame orients and locates the related features to the specified datums.

The lower horizontal frame locates your pattern of features to each other by more more than 0 at MMC or .002 at LMC, however the tolerance boundaries are ONLY ORIENTED to the specified datums (if specified).

In this case the lower frame does not have any datums spcified so it only locates the pattern of features to each other 0 at MMC and .002 at LMC.

Another look: If you have hole feature and they are manufactured at Dia. .5000 the hole features must located to each Basic by not more than .001.

The Circle M means Maximum Material Condition - and gives you a variable sized (bonus tolerance) tolerance boundary dependent on the as-manufactured size of the related features.

You should consider getting a GD&T book BTW:







Modified by Kelly Bramble at Tue, Nov 23, 2010, 10:56:14


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: : True position with a diameter of 0? -- Kelly Bramble
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Dimensioning & Tolerancing GD&T Forum
Posted by: billtheenemy

11/23/2010, 12:50:01

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Kelly,

Thanks for your reply. I have access to a GD&T book in the office, but will probably need to get one for my own use.

I'm still not sure I understand what you mean. What do you mean by "pattern of features?" I can't post a picture of the part (it is sensitive material), but there is a through-hole. A slot interrupts the through-hole, which is not visible in this view.

-Bill








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Posted by: Kelly Bramble

11/23/2010, 18:28:04

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A pattern of features would mean that there are more than one feature (hole) to be tolerance controlled.

In your case it appears that the pattern of features is the coaxial(?)hole features separated by the slot. The tolerance given by the lower horizontal frame is meant control the relationship of the two holes to not vary relative to each other by more than 0 at MMC, .001 at Dia. .500, and .002 at Dia. 501.








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Posted by: billtheenemy

11/23/2010, 18:46:41

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Ok, that makes sense. Thanks a lot. You have been very helpful.

-Bill








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