×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Datum Target

Datum Target

Datum Target

(OP)
I have a print that has datum targets sitting next two linier dimensions. two pins in an assembly same size on a coaxial line. pin diameter is ref position to A datum targets are A1 and A2. this to me is not a valid way to apply the datum targets

this is what I understand to be correct
Datum targets are attached by a solid or dashed line to point, line or phantom line of the desired shape

RE: Datum Target

Any change at attaching a sketch?

Certified Sr. GD&T Professional

RE: Datum Target

Woops. Any "chance" at... (typing and edit skills were off-line)

Certified Sr. GD&T Professional

RE: Datum Target

(OP)
Here is a quick sketch of how they applied the datum target

RE: Datum Target

Sketch did not attach.

Certified Sr. GD&T Professional

RE: Datum Target

Got it. Will respond this afternoon.

Certified Sr. GD&T Professional

RE: Datum Target

rje2019:

From a symbology standpoint, paragraph 4.24.1 in Y14.5-2009 defines what is allowed. Your sketch, which has direct contact with the "balloon", does not meet the requirement. So I agree with your statement "Datum targets are attached by a solid or dashed line to point, line or phantom line of the desired shape"

I also have concerns with the application of the position tolerancing. Not knowing the design requirement and what someone is attempting to communicate with the symbols, I cannot offer commentary. But does figure 4-24 in 2009 mean anything?

Certified Sr. GD&T Professional

RE: Datum Target

(OP)
ok Thanks for confirming first part

their intention was to establish a datum A thru the pins( they are fairly far apart) as called out the feature frame is referencing datum A that it creates, which make is not valid. I was planning on recommending two options. left side diameter becomes datum A and right side positions to datum A and becomes Datum B. then future frames use A-B. the other is what you listed, standard 4-24, 7.6.2.3 position no datum reference becoming datum A. that last option they should understand a little easier

RE: Datum Target

rje2019:

Your datum B positioned to datum A approach is Ok. But... caution should be used since the projection of datum axis A across the "long" distance to the pin on the other end may not offer desirable results. I might recommend controlling the datum A feature perpendicular to a planar feature (I call it datum C) and then controlling the datum B feature using position to C and A (secondary).

Certified Sr. GD&T Professional

RE: Datum Target

Datum D is not valid - datums are derived from physical features (datum features) and not from theoretical points/lines/planes or the intersection with theoretical points/lines/planes.

That being said I'm not even sure what you're trying to accomplish with that or what intersection you would be referencing since datums B and C look to be coplanar.*

*Edit - looks like theres two datum features referenced as "B", a 24.00 width and a 2.00 diameter, this would need to be fixed. Regardless my first statement still applies.

RE: Datum Target

rje2019:

It look like you "missed" my example. I was thinking: the left face of the 24.00 width would be specified as datum A. The 2.00 hole on the left would be perpendicular to datum A and be designated datum B. The 2.00 hole on the right face would be positioned to A primary and B secondary and could be specified as datum C. Hole XXX would be positioned to B-C. Note: There may be other relationships between part features that impact the final GDT tolerancing schema. I would need an in-depth understanding of part function to even attempt an approach. And this is beyond the purpose of this format for me.

Certified Sr. GD&T Professional

RE: Datum Target

Also this seems to be a very similar scheme to what you posted previously (https://www.eng-tips.com/viewthread.cfm?qid=451052) and my suggestion at the end of that thread (which remains unanswered) still applies about referencing features of a common size as a pattern (ie: 2x dia 2.000) as a single datum.

RE: Datum Target

chez311: Thanks for the input. I didn't follow the other thread you mentioned.

Certified Sr. GD&T Professional

RE: Datum Target

(OP)
Mkcski Ok I stand corrected with your example and yes this is a more complex part there is a lot going on with it

chez311 yesterday I had to ask what they intended with D. they were looking at datum D as the last step to the degrees of freedom. A axis, B datum on 24.00 and D. thier example C already does this.
yes one of the options is two datum features single datum axis. have not heard back on what they think of that yet

RE: Datum Target

rje2019,

There is no need to specify a datum D as the intersection (nor is it allowed) of B (on the 24.00 width) and C. If referencing B|C in a FCF the width datum feature establishes a centerplane which is orthogonal to the 2x orthogonal planes established by C at the point shown.

Quote (rje2019 2 Apr 19 20:08)

yes one of the options is two datum features single datum axis. have not heard back on what they think of that yet

Something to keep in mind - if it as shown first dia 2.00 is datum A and second dia 2.00 is datum B referencing A and then referencing the pair as A-B on other controlled features you are adding an additional step which results in stacking of tolerances. This becomes a little more ambiguous when utilizing MMC/MMB but you will certainly see the effects at RFS/RMB.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

eBook - The Future of Product Development is Here
Looking to make the design and manufacturing of your products more agile? For engineering and manufacturing organizations, the need for digital transformation of product development processes just became more urgent than ever so we wanted to share an eBook that will help you build a practical roadmap for your journey. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close