Datum Target Lines: Not sure what this means

[Saladsamurai]

Hello All,

Perhaps I could have some guidance on this. I have created a sketch below that replicates something that I have on a Drawing. I am a little confused about the use of the datum target lines (DTL's) "A" and how to interpret them. Furthermore, I am not sure what to call this particular use of them so that I can better search them online (is there a specific name for this use of DTL?). I have looked in ASME 14.5, but I am coming up short (that might be due to my inexperience at this).

Can anyone offer any insight or references to this usage? I can see that they are trying to set up a datum plane, but I am not sure exactly how. What exactly are they telling the inspector to do? Why do we need 4 DTL's?

Thanks for your time.



Using NX 7.5.3 & Teamcenter 8

 

[MadMango]

Looks like fixturing in two 90deg V-blocks.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[Saladsamurai]

Hi MadMango.

I think you are correct. I just found the section on "Equalizing Datums" pg 73 in ASME 14.5-1994 (but it looks like they removed this section from the 2009 standard...not sure why?). So, since we are showing 4 DTL's, we need 2 V-Block Knife-edge equalizers correct? I am still unclear on why we need 2 equalizers.

Using NX 7.5.3 & Teamcenter 8

 

[axym]

Saladsamurai,

I would agree that 2 V-shaped equalizers are appropriate. They could be knife edged, but could also be round pins.

Two equalizers are necessary to stabilize the part. I would imagine that these datum targets are defining the secondary and tertiary datums, and not the primary. The line down the centerline of the two equalizers would be one axis (say the Y) of the datum reference frame.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[Saladsamurai]

Hi axym,

Yes; you are correct. "B" (not shown) is the primary and it seems that 2 equalizers make up the secondary and tertiary as you have stated. It makes sense now. Thanks again folks.

Using NX 7.5.3 & Teamcenter 8

 

[DaSalo]

The key is that the alignment of the two v blocks is relative to an implied 0 position and 0 angle. So they are telling you to use two Vblocks that are perfectly in-line with each other and perfectly oriented to each other. Without the implied 0's the axis doesn't get correctly established down the major axis of that ellipse.

CATIA V5 R20
PC-DMIS 2011 MR1