Position tolerance, Double-D Hole

[thepete]

See picture above(which hopefully posts)

I'm trying to use GD&T (Y14.5-2009) to tolerance the flats of the D-hole. What I'm trying to describe is the flats centered on the 1.125 diameter hole.

I also have to do something similar with the shaft that fits through this hole.

Position tolerance I have doesn't feel quite right. What are your thoughts?

Thanks,
Pete

(apologies to those who've seen this in a different (wrong) section of the forum.)

 

[Belanger]

If you can live with the tolerance values to be the same (the size and the position tolerances for the entire hole), profile of a surface ("all around") is the easiest way, rather than the position symbol.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[TheTick]

You don't really need the basic .438 dim.

 

[TheTick]

Dimension the Ø.125 as vertical length tangent-to-tangent.

 

[cjccmc]

I would put the D on the 1.125 dia. As is it seems that you only want the one arc as defining feature for D.

 

[KENAT]

Picking up from where I was in thread404-351660...

You already have a control on parallelism of the straight edges to -B- from it being referenced in the position fcf for the .875 width.

Also as I said before .438 is not essential.

Posting guidelines faq731-376

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

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

 

[pmarc]

I see nothing wrong with the dimensioning of flats as long as there is true functional reason to control the flats to 1.125 diameter and not to |A|B|C|. Referencing to |A|D|B| means that design intent is to have the width perpendicular to datum plane A, centered at datum axis D and parallel to datum plane B. Quite clear.

As it was mentioned, basic .438 is not needed.

Additionally diameter symbol preceding tolerance value in positional FCF for 1.125 diameter is missing.

You should also consider applying two perpendicularity tolerances controlling mutual relationship between datum features A, B and C:
1) for datum feature B - perpendicularity to |A|;
2) for datum feature C - perpendicularity to |A|B|.

 

[CheckerHater]

Also consider applying flatness tolerance to datum feature A

 

[fsincox]

I suspect B & C are really just manufacturing datums, not important to the function!
Frank

 

[CheckerHater]

According to ASME Y14.5-2009 paragraph 4.9 datum features now “shall be controlled”, and according to sub-paragraph a) of said paragraph, form of primary datum feature is first on the list.

 

[pmarc]

According to the very same paragraph 4.9 form of primary datum feature may be controlled "indirectly by dimensions such as the size of primary datum feature of size".

 

[CheckerHater]

Since when flat surface is feature of size?

 

[pmarc]

Flat surface is not feature of size, but flatness error of the flat surface is indirectly controlled by size tolerance applied to .125 dimension through Rule #1.

 

[CheckerHater]

I agree that the size tolerance will indirectly control flatness of derived median surface or something of a kind.

However, using size tolerance to control flatness of ONE particular side you have chosen to be your datum feature introduces some ambiguity, don't you think?

 

[pmarc]

No, I do not think so.
If we assume for a moment that tolerance for .125 dimension is let's say +/-.005, allowable flatness tolerance for both sides of the plate will be .010.
What is ambiguous with that?

 

[Belanger]

CH -- flatness of a surface is indeed controlled by the size dim. It's not just the median plane, but each surface. (I can do a sketch later today if needed.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[thepete]

I'll have to make a point to follow this forum more. I think I'll learn a lot.

 

[CheckerHater]

No need for the sketch.

I am just trying to say, that you have to assume the worst, unless you actually specify flatness for one side.

Now the question is "which side?" We have symmetrical part that can be flipped over.

According to another fun paragraph, 4.8, we may have to add identifying feature to tell one from another. Good thing is we "may", not "shall", but I feel slightly uncomfortable adding non-functional feature just to satisfy requirements of the drafting standard.

 

[pmarc]

If .010 of flatness error is acceptable from functional point of view, I really see no reason of applying additional flatness tolerance - although conceptually it is quite simple tolerance to understand, in reality its verification may cause serious pain. Plus, adding it will not solve the problem of symmetrical part at all.

 

[CheckerHater]

Verifying flatness of flat part causing serious pain? I am out.