Hole Position Tolerance Question 1

[T105]

Hello,

In the attached jpeg, There are two datums defined for the position of the Diameter 5 holes. The GDT box defines the position of the holes with respect two Datums A, B and C.

There is no defined relation for the location of Dia. 5 holes with respect to Datum C (dia 3 hole). How are the location of the Dia 5 holes effected wrt to Datum C? How should the tolerance table for these holes shape up with respect to changes in the datums?

Best regards

 

[dingy2]

Datum C is only used for anti-rotation about datum B. All dimensions come from the centre of the part which is created by datum B. I see that datum C is also in alignment with two (2) of the positional holes in question so there definitely is a relationship.

This drawing is one of the better ones out there and it reflects that the Designer has a relatively good understanding of GD&T.


Dave D.

http://www.qmsi.ca

 

[T105]

Thank you for your response.

What I understand from your explanation is the Datum C only relates the orientation of the two holes. It does not express any relation with respect to dimensions.

In the attachment, there is a slightly modified orientation of the holes. What do you say about this version. Is it correct in terms of meaning usage considering the tolerance of the holes with respect to Datum C?

 

[dingy2]

Both drawings are good except the last drawing required a theoretical dimension to the hole shown as datum C.


Dave D.

http://www.qmsi.ca

 

[CheckerHater]

Actually Datum C on the original drawing locates all 4 holes.
It's just the basic angle dimensions are "invisible"; 0 deg and 90 deg basic angles are usually IMPLIED.
From the appearance of the dimenssions the drawing is coming from ISO country. Does anybody know if there is big difference between ISO and ANSI/ASME when it comes to implied angles?

 

[KENAT]

Yep, in both datum C appears to to be the 'clocking' datum for the 4 holes.

The drawing is indeed taking advantage of implied 90°.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[pmarc]

Generally saying there are no significant differences between ISO and ASME in terms of implied angles. If we are talking about patterns of holes, ISO does not have SEP REQT note for 'separate requirements' concept - it uses more descripitive texts under the FCF. ISO 5458 deals with this thread.

 

[CheckerHater]

Thank you pmarc,

It was my general impression, but it is always better if someone knows for sure.

 

[T105]

Thank you very much for all the answers.

Best regards,
Oykun