4 Datums Referenced in a Print (Drawing) Feature Control Frame

[Mr. Friend]

I am new here. I received a print that has 4 datums reference in a feature control frame. The FCF looks like thus: A/B/C/D
I thought I was pretty good with Y14.5-1994 & 2009. Is this legal?

 

[Stijloor]

I am new here. I received a print that has 4 datums reference in a feature control frame. The FCF looks like thus: A/B/C/D
I thought I was pretty good with Y14.5-1994 & 2009. Is this legal?

Just to make sure we understand your question:

Is it A B C-D?
Or contained in multiple FCF's?

Can you describe it in more detail?

 

[David DeLong]

Four separate datums are not legal but I have seen it in the past. If you have, like Stijloor stated, a C-D which is only 1 datum using 2 features, then it is legal.

 

[Mr. Friend]

Thank you for the response. There is no datum marriage (i.e., E-H). The print asks for the surface profile of a feature to be within .010 of G, D, E, and H. Essentially, primary G (plane) halts the translation of Z and rotation about X. Secondary D (plane) halts rotation about Z. Tertiary E (hole) halts translation along Y. The forth datum, datum D, is a the center of an elongated hole, and is located within the datum G feature, perpendicular to G.

So we have to be within .010/G/D/E/H/

 

[Paul F. Jackson]

In the 2009 Standard Customized datum reference frames are introduced where datum features may be restricted from constraining degrees-of-freedom that they may otherwise be capable of in their hierarchical designation. It is necessary to label the axes in the drawing to decipher the rotations or translations that have been released or transferred to another feature.

So yes it is legal to have four datum features and possibly more when constructing a customized datum reference frame.

CMM programmers sometimes errantly create a customized datum reference frame by moving the coordinate reference to some intersection point of features other than those that the coordinate system was created from. This new tool will enable that practice when necessary.

Paul

 

[Jim Wynne]

Technicalities aside, your customer might not want to give any ground unless there's something in it for them. If you were to explain the redundancies to your customer and hint that the additional unnecessary inspection time might result in the piece price being revisited, you might get their attention.