Datums Defined by Targets - Can Have Modifiers?

[pmarc]

It is allowed to have datum callouts specified at MMB even if datum targets are used to establish a datum. If you are trying to establish datum axis based on e.g. 2 sets of 3 datum target points you can defined them on RMB (RFS) basis or MMB (MMC) basis.

Y14.5M-1994 did not specifically offer such possibility. Paragraph 4.6.4 is only mentioning RFS option.

Y14.5-2009 introduces MMB option in paragraph 4.24.10.

 

[MechNorth]

As pmarc indicated. It was a good addition to '09.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[Madhu454]

I was not aware of this. I have only 1994 std with me.
Thanks for the clarification.

 

[dingy2]

Madhu454:

I agree that 4.24.10 does reflect that MMB is applicable in the situation shown. In figure 4.51, we have a positional tolerance on a hole shown on a cylindrical part. MMB can be used on the datum structure and it does make sense.

We had a solid feature illustrated in 4.24.10. If we have a datum target structure on a non-feature such as shown in fig. 4-39, page 79, of the 94 standard, could we still use MMB? I don't think so.

I guess we would really have to see your drawing to positively state that MMB can be used in your situation.

Dave D.

http://www.qmsi.ca