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GD&T for assembly 3

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mousepotato

mousepotato

Mechanical
Jul 1, 2003
62
Hi guys,

I work as a designer with sheet-metal parts. I would like to know if there is a difference between
1. GD&T for Assembly,
2. GD&T for Manufacturing and
3. GD&T for Inspection.

If there are differences, how can you differentiate between the drawings for these?

I also wondered if somebody can share a very well constructed drawing of a sheet-metal component with
1. An important functional profile (like a CAM/Follower) and
2. With atleast 4 datums and
3. Many flanges at different angles and lengths and
3. A number of slots and holes at different angles in these flanges.

Any help would enlighten me and whole-heartedly appreciated.
Thanks in advance.
 
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GD&T is supposed to be for defining functional requirements, deviations from that, are compromises done to solely assist those various groups.
Frank
 
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Why are at least 4 datums a requirement here? It's not wrong to have four datums specified on a part (but definitely NOT in a feature control frame) but I don't understand why that has to be a requirement if three datum is sufficient.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
 
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Fundamentally the GD&T is the same regardless of user or process so no real difference for your 3 classes.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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Regarding the first part of question i guess mousepotato might be asking about datum feature precedence in the feature control frame.Datum feature precedence is for manufacturing sequence or for inspection or for assembly or for all three.
 
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Datum precedence is absolutely not for manufacturing sequence. It is solely for inspection setup. That is all. I'm sure that such an absolute statement will meet with resistance. Absolutes usually do around here.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
 
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Well I'd go further still and say the datum precedence should be derived from functional considerations.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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@KENAT

Wouldn't the world be a beautiful place if that was considered more often...

_________________________________________
Engineer, Precision Manufacturing Job Shop
Tool & Die, Aerospace, Defense, Medical, Agricultural, Firearms

NX8.0, Solidworks 2014, AutoCAD LT, Autocad Plant 3D 2013, Enovia DMUv5
 
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I agree with that statement Ken. I was talking about precedence once it's been established.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
 
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Any drawings? Anyone? Just to refer....thanks in advance.
 
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Mousepotato,
A tolerance can certainly be applied to an assembly. In that event the tolerance appears on the assembly drawing and dimensions are not generally required. For example, if two cylindrical feature are to be assembled coaxially then a positional tolerance can be applied if datums are assigned to the two diameters in the assembly drawing. In any event, the tolerance is intended for inspection, manufacturing, and engineering BUT, as with drawings in general, it delineates an end-item, functional requirement for engineering and inspection purposes that manufacturing must satisfy at the assembly level.

Tunalover
 
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mousepotato,
I will not help you with the second part of your original question, simply because I do not have access to any sheet-metal component drawing, but I think the attached file may interest you when it comes to differences between GD&T for assembly (function), manufacturing and inspection. These are four pages taken from Alex Krulikowski's book "Advanced Concepts of GD&T". In my opinion the example being discussed there very nicely emphasizes the importance of functional approach to dimensioning and tolerancing.

 
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Star to pmarc for sharing this file.Excellent piece of information.Thanx pmarc.
 
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