True position callout 2

[Rwelch9]

Hi ,

Please see attached sketch.

I am looking for advice on a drawing i have .

I have 3 holes with a callout to Datum feature A

As this is just a callout to A alone , theoretically could the holes be any relationship to each other ?

The 2x Ø4mm dowel holes will have to be positionally good.

What about the Ø3mm dowel hole.

I did not add any basic dimensions etc.

I was more questioning exactly what the drawing is asking for in terms of the position of the 3 holes to Datum A

Datum B is in the print but no feature is related to it any way. Which i thought was strange.

There is no datum c or orientational control on the drawing.


Thanks

R

 

[chez311]

I have 3 holes with a callout to Datum feature A

As this is just a callout to A alone , theoretically could the holes be any relationship to each other ?

As was stated in several of your threads previously, these would be considered as part of a single pattern due to simultaneous requirements. The tolerance zones for these 3x holes would be fixed in basic location/orientation to each other, and any other feature with a position or profile tolerance to |A| unless otherwise specified.

Of course as you know, you need these basic dimensions to be specified on the drawing. I assume you left them off because this is only a sketch.

The 2x Ø4mm dowel holes will have to be positionally good.

What about the Ø3mm dowel hole.

What about it? All 3x holes have the same size tolerance specified (2x 4mm and 1x 3mm). If "positionally good" means within 0.018 to you, then you're covered. If not, you may need further refinement.

Datum B is in the print but no feature is related to it any way. Which i thought was strange.

If it is not referenced, it should be removed. Or perhaps it should be referenced and is missing from your FCF's, depending on the functional requirements its pretty common to utilize a flat mating face.

 

[Rwelch9]

Chez311

The only thing i was not sure of was if simultaneous requirements only worked with hole features of the same diameter .

So thanks for clearing that up.

I know it has been mentioned a few times on my previous posts .


Thanks


R

 

[Jacob Cheverie]

Rwelch9,

Simultaneous requirements are such that any geometric tolerances referencing the same datum reference frame (in the same order and with the same material modifiers) must be evaluated to the same datum reference frame. This means that if datum displacement is being used to optimize the result of one geometric tolerance, the displacement must be consistent in magnitude and direction while evaluating all of the other geometric tolerances meeting the criteria for a simultaneous requirement.

For example, if you had four holes with a position tolerance to A|B(M)|C(M) and datum feature B has departed from it's MMB enough to utilize datum displacement, or datum shift, it can't shift one way for one hole, another way for another hole, etc... The part may not actually mate in it's application.

 

[chez311]

The only thing i was not sure of was if simultaneous requirements only worked with hole features of the same diameter .

The only thing I would add is to take a look at Y14.5-2018 fig 7-46 and accompanying text para 7.19 - simultaneous requirements applies to position AND profile tolerances, as long as they reference the same datum features, in the same order of precedence, and the same boundary conditions. This means not only do they not have to be holes of the same size, they can be features of any size/type/shape and still be held in simultaneous requirements as long as a qualifying position or profile tolerance is used - ie: in fig 7-46 the 4x holes (0.05(M) position to |A|B(M)|) and outside contour (1 profile to |A|B(M)|).