Datum shift with two feature

[Sa-Ro]

If datum A is produced at MMC, then no datum shift available for dia 10 and dia 5 holes.

If datum A produced at LMC 20.1, dia 10 and dia 5 hole position tolerance may shift by 0.1 per side.

Actual part:
Dia 20 hole:
Hole size 20.1

Dia 10 hole:
Hole size dia 10
Produced at 25.15( 25 basic + 0.05 position tolerance per side + 0.1 datum shift per side) - maximum possibility

Dia 5 hole:
Hole size: dia 4.9
Produced at 25

In this condition, though datum shift is available. The dia 5 hole will not allow to move.

How can I represent in my drawing?

Can I use datum shift in this condition?

Note:
I am drafting a rear flange component which is having 10 holes and one slot.

Before going to that component, I am splitting my doubts as simplified for me to understand.

 

[chez311]

I would take a look at the below thread especially CH's post on (17 May 18 14:59) the figure i think does an excellent job showing what datum feature shift is and is not, and it looks very much like your sample case.

https://www.eng-tips.com/viewthread.cfm?qid=439000

 

[Sa-Ro]

From CH post, my understanding

Though datum modifier applied, it can not be used for multiple features at simultaneous requirement. Only positional tolerance can be used.

Here is my flange component (partial).

Now, the dia 28 TP can shift, 0.6 total (0.3 either side) in horizontal from datum B and 0.4 total (0.2 either side) in vertical from datum C wrt datum ABC.

Dia 6.6 hole horizontal position controlled by datum B and vertical position controlled by datum C.

Dia 6.6 TP is allowed to shift 0.1 total (0.05 either side) in horizontal from datum B.and 0.4 total (0.2 either side) in vertical from datum C.

Though datum C allow 0.4 total tolerance in vertical, Datum B restrict to 0.1 total tolerance.

How to handle this?

Shall I consider, Though datum C allow 0.4 total tolerance in vertical, precedence datum B override the datum C tolerance and dia 6.6 hole TP can shift by 0.1 total tolerance only?

or if any other feature restricting 0.4 tolerance from datum C, the maximum movement can be considered for vertical datum shift?

Is there any possibility to limit the datum shift like one available in geometrical tolerance?

 

[Tarator]

Sa-Ro,

I am not sure what your intent is. Maybe if you could share the mating part(s), it would be easier to see the design intent, so appropriate datum feature selection can be done.

Datum shift would allow you to accept more parts (good for production) if "centering" is not critical for you. If the pin (mating part) that goes into the hole D is not interference fit, there would be a play in the assembly. Typically, M datum feature modifier would represent a more realistic assembly scenario.

Here could be a possible solution to give you an idea based on my assumption:

You would only need 2 datum features (A and D) to control 4 holes and the perimeter of the part. Simultaneous Requirement would apply.

 

[Sa-Ro]

I have updated my drawing and completed the part.

Tomorrow I will share the part drawing.

 

[Sa-Ro]

@ Tarator

Please visit:

https://www.eng-tips.com/viewthread.cfm?qid=470328