orientation or form error considered in min wall thickness stack? 1

What drawing standards are you working to, or more specifically are you invoking envelope principle?

The sketch shows asme y14.5-2009.

Position of your smaller hole is specified at RFS.
Is it the same in your textbook?

bxbzq, are you familiar with the envelope principle that is generally invoked by 14.5?

I believe that answers why your text book gets the answer it does.

Yes. The hole is positioned at RFS base. The example is from Alex's fundamental gd&t book which is based on '94.
I think '94 and '09 would not be different for case like this, would it?

envelope principle, rule #1, perfect form at MMC, not perfect form at LMC, right?
In this calculation I'm dealing with holes at LMC. Am I missing something?

ASME Y14.5M-1994 2.7.1.2(c) said:

There is no requirement for a boundary of perfect form at LMC. Thus, a feature produced at it's LMC limit of size is permitted to vary from true form to the maximum variation allowed by the boundary of perfect form at MMC.

Click to expand...

Unless I'm missing something the 'variation in form' has to be in the direction of MMC - so adding material not removing additional material.

I think the tolerance zone Ø0.4 should be zero on both of your scenario #1 1nd #2, since the bonus tolerance are automatically included in the analysis for the calculation of min distance, there is no step #4 (-0.2) on the list.

SeasonLee

I get an answer of 2.7 minimum (but see my next paragraph). As the large hole gets bigger it doesn't affect datum B, because that's created from the Related Actual Mating Envelope (to use the 2009 terminology). However, the actual hole that we call datum feature B could have a larger "sweep" around the top because as that hole departs from MMC it could tilt up 0.2 in any direction. That's why our answer is different from the textbook, Bxbzq.

The real issue is whether the person asking the question is worried about the wall thickness "X" as a consistent thickness (which is why the texbook answer didn't include the bonus tolerance on the large hole), or just the worst case at any cross-section of the hole such as at the top face or rim (which Bxbzq and I are thinking of -- Scenario #1 in the OP).

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

bxbzq,

I get 2.7mm if I treat the Ø10mm hole as having a positional tolerance. It doesn't. It has perpendicularity to datum[ ]A. It is datum[ ]B. It has zero positional error, by definition.

There is no MMC specification on the datum[ ]B called up on the Ø3.4mm hole, we must consider the Ø10mm hole to be centred on the datum. This will be fun to measure. Sloppy holes make poor datums.

The wall is...

10mm - 3.6mm/2 - 0.2mm/2 - 10.4mm/2 = 2.9mm.

It has been pointed out by Dingy that FOS[ ]datums can be fixtured if they are called up at MMC. This changes the answer.

10mm - 3.6mm/2 - 0.2mm/2 + 10mm/2 - 10.4mm = 2.7mm.

--
JHG

JHG -- while datum feature B has no position tolerance, it does gain tilt if the hole is enlarged. This tilt doesn't change datum B itself, but it does bring the rim of the hole somewhat closer to the other hole, thus reducing the distance X at that rim by another 0.2.

IOW, you're partially right that with no MMB modifier on datum B, "we must consider the Ø10mm hole to be centred on the datum." However, the Related AME of the hole is what's centered on the datum, but that doesn't consider the actual possible rim of the hole. See the sketch in the OP for Scenario #1.

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

Looks only Belanger is with me.

drawoh and SeasonLee, the ø0.4 is not position tol. However, there could be orientation and form errors when the hole gets larger than MMC. Think about this, just look at datum feature hole B itself, what is max distance from its axis (datum axis B derived from datum simulator at related actual mating envelope) to the furthest point on an actual hole at LMC size? In scenario #2, it is 5.4mm. In scenario #1, the max distance could be even greater than 5.4mm, depending thickness of the plate to calculate the allowed tilted angle of the hole. On sheet metal parts, it could be a quite big number.

kenat, are you saying only barreled or waisted shape allowed if the hole's max dia. is at LMC? Being curved hole like shown in scenario #2, there is no more material removed. It's just that, curved shape. Actual local size at any cross section equals to LMC size.

bxbzq,
Not only J-P is with you.
2.7 is what you should get in this case.
2.9 would work if the smaller hole was positioned to B only, and not |A|B|. In |A|B| case you have to take tilt of datum feature B surface into account, exactly as you have shown on Scenario #1 sketch.

I have some comments though.
Both of your scenarios show incorrect inner boundary of smaller hole. That said, if the hole is positioned at RFS and is at its least material condition (3.6), the inner boundary is 3.4, not 3.2.

Now, using your sketch #1 to create a stack-up, we will get (starting at your zero):
-0.2 -- stack-up start point -> right edge of 3.4 inner boundary;
-1.7 -- right edge of 3.4 inner boundary -> center of 3.4 inner boundary;
+10.0 -- center of 3.4 inner boundary -> center of 10.0 virtual condition;
-5.0 -- center of 10.0 virtual condition -> left edge of 10.0 virtual condition;
-0.4 -- left edge of 10.0 virtual condition -> stack-up end point
-----
+2.7

Another thing, part's thickness in scenario #1 has no influence on stack-up results. The thicker the part, the tilt angles will be smaller, but distances in stack-up direction will not change, so the result will always be 2.7

I don’t think datum feature will ever tilt outside of 10.4 (5.2 RAD).
As your perpendicularity tolerance is zero you cannot really “add” it to calculate virtual condition.
Your hole should always stay within 10.4 envelope. it looks like OP is “double-dipping”, taking 10.4 hole and tilting it another .4, while in fact tolerances are reciprocal:
You have perfect 10.0 hole which may EITHER tip 0.4 while staying 10.0, or stretch to 10.4 while staying perfectly perpendicular. Either way 10.4 envelope is maintained.
Because of that in Scenario_1 0.2 should be dropped, and in Scenario_2 5.4 should be 5.2
Just my 2 cents

CH,
If the datum feature hole is at 10.4 it can be 0.4 out of squarness. That generates outer boundary of dia. 10.8=10.4+0.4. Which means that extremities of datum feature surface can be 10.8/2=5.4 max radially from datum axis B.

This whole excercise can also be treated as a calculation of distance between outer boundaries of the holes, which centers are spaced basic 10.0 apart, and not their inner boundaries. So:
- outer boundary of datum feature hole is 10.8 (10.4+0.4);
- outer boundary of smaller hole is 3.8 (3.6+0.2).
Which gives: 10-10.8/2-3.8/2=2.7

Another term of the 10.8mm boundary is resultant condition.

pmarc,
I agree if the smaller hole at LMC, the boundary is at ø3.4, but I don't agree you call it inner bounday. Because inner boundary is a constant boundary generated by MMC minus geo tol. In this case it should be 3.4-0.2=3.2mm. Maybe related AME is correct term.

pmarc said:

If the datum feature hole is at 10.4 it can be 0.4 out of squarness.

Click to expand...

No, it cannot. Your "squareness" tolerance is zero.

In order to "tilt" something, say, 0.2, you have to BORROW 0.2 from your "size" requirement, so now your hole is only 10.0-10.2.

This is fundamental principle known as "Rule 1" or "envelope requirement".

Both size and shape are confined within the same enverope - the more of one means the less of the other.

bxbzq said:

Another term of the 10.8mm boundary is resultant condition.

Click to expand...

Resultant condition = Largest hole + Position/orientation tolerance.

Largest hole = 10.4

Position/orientation tolerance = 0

10.4 + 0 = 10.4

CH,

2.8.3 Effect of Zero Tolerance at MMC
Where a tolerance of position or orientation is applied
on a zero tolerance at MMC basis, the tolerance is totally
dependent on the size of the unrelated actual mating
envelope of the considered feature. No tolerance of posi-
tion or orientation is allowed if the feature is produced at
its MMC limit of size; and in this case, it must be located
at true position or be perfect in orientation, as applicable.
Where the size of the unrelated actual mating envelope
of the considered feature has departed from MMC, a tol-
erance equal to the amount of such departure is allowed.
The total permissible variation in position or orientation
is maximum when the feature is at LMC, unless a maxi-
mum is specified.

Also see fig. 2-12.