Composite FCF with three callouts

[LargeNCharge86]

I'm having a tough time figuring out how best to call this out.

I have three weld studs welded to a bracket. I need to control:

2.0mm perpendicularity of each stud to datum A
1.5mm TP of the stud pattern to A, B & C
0.5mm TP of the studs to one another.

How can I call this out correctly? I feel like it's not right to have this as three lines in one FCF.

 

[mkcski]

LargeNCharge86

Given your requirements, the perpendicularity is a refinement of the position to A,B,C. so the perpendicularity tolerance must be less than the position tolerance. Since this is a pattern of features, I suggest something like that shown in Y14.5-2009 figure 7-44 on page 140. The upper FCF would be A,B,C the middle FCF would be just datum A, and the lower frame would have NO datums. The tolerances must decrease smaller form top to bottom.

Certified Sr. GD&T Professional

 

[mkcski]

LargeNCharge86

Sorry, I meant figure 7-45 (not 7-44).

Certified Sr. GD&T Professional

 

[pylfrm]

LargeNCharge86,

Sounds like the following composite position tolerance would do the job:
[tt]
| diameter 1.5 | A | B | C |
| diameter 0.5 | A |
[/tt]
The upper segment controls position of each stud with respect to the datum features. As a side effect, it also ensures the perpendicularity error is 1.5 or less, so there is no need to explicitly apply your larger tolerance.

The lower segment controls position of the studs to one another. Because I included the reference to A, it also controls orientation. This is usually required required in the scenario you describe, but if you really mean what you said, then the lower segment should have no datum feature references at all.


pylfrm

 

[mkcski]

LargeNCharge86:

No one has mentioned this, but be sure to consider the use of MMC material condition modifier if the design allows.

Certified Sr. GD&T Professional

 

[drawoh]

mkcski,

How would MMC (MMB?) affect the position of a stud?

--
JHG

 

[mkcski]

drawoh:

There appear so be not FOS datums, MMB is not applicable. But MMC could be considered for a external FOS - a stud.

Certified Sr. GD&T Professional