Tolerance Stack Question 1

[pmarc]

I just need a double check on following tolerance stack calculation. What would be the minimum and maximum distance between bottom surface of the part (datum feature C) and hole surface using worst-case approach?

 

[pmarc]

Forget about first sketch - no basic dimensions for hole were given there.

 

[ctopher]

This may help:

http://www.engineersedge.com/true_position.htm

Chris
SolidWorks 10 SP4.0
ctopher's home
SolidWorks Legion

 

[KENAT]

For us to 'double check' shouldnt' you tell us what you think it is?

I'm thinking...

X=30-1/2 max hole dia-1/2 pos tol dia - 1/2 MMC bonus tol.

However, in practice since B & C don't have physical datum identifiers it will be tricky to say which is 'X' and which is the other side of the hole on a real part.

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[pmarc]

KENAT,

Let's say there is a groove thru the upper surface of the part, so there is clear indentification which surfaces are datum features.

I am asking because I want to check if datum features perpendicularity controls should be somehow involved in this calculation. In my opinion yes, so I would add to the formula you gave perpendicularity factor.

 

[KENAT]

I suppose it depends on your definition of 'X'.

If it is the distance from simulated datum C then I think what I put is right.

If it is the distance from 'lowest point' of datum surface C then I suppose yes, you should also subtract the perp.

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[drawoh]

pmarc,

The smallest distance X occurs when you have the largest hole at lowest allowable position. I am assuming that X is located from Datum_C. This is not necessarily the same thing as the distance from the actual edge.

Note that with the hole at Ø15.2mm, your positional tolerance is Ø0.3mm.

X_min = 30mm - 15.2mm/2 - 0.3mm/2 = 22.25mm.

Datum_C is the portion of your bottom edge that touches your fixture. This means that the maximum perpendularity error will be towards your hole. This could bring your separation down another 0.1mm.

JHG

 

[pmarc]

Kenat,
I was rather thinking of distance between part features not the hole and simulated datum feature C.

For your information my original calculation was:
MAX = 22.55
MIN = 22.15

 

[Belanger]

The max is 22.55. The min is 22.25
But that's assuming you are asking for the distance from "datum C" to the hole's rim. If you are asking for the distance from "datum feature C" to the hole's rim, then the min would be 22.15 because of the perpendicularity's effect on the form of the bottom surface.

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

 

[SeasonLee]

Belanger

There is no doubt about the perpendicularity’s effect on the form, will this also effect on the max 22.55 and result at 22.65 ( 22.55 + 0.1 ). Please let me know if I am wrong.

SeasonLee

 

[dtmbiz]

SeasonLee,

I agree with Belanger because of rule #1.... Perfect form at MMC

max value: 22.55

 

[Belanger]

It's still 22.55, because the position of the hole is from datum C, and datum C is always formed by the high points along the bottom surface. So there's no additional maximum due to form; only the minimum is affected by form.

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

 

[SeasonLee]

Thanks Belanger,what you said is exactly right.

SeasonLee

 

[Belanger]

Sure, SL. Stacks are always fun, aren't they?



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

 

[BLUEHONDA]

Hello i am a bit new to this mechanical stuff and i am trying to understand how you worked this out?

Would sombody break it down for me so that i can understand each part.
drawoh, How did you get the positional tolerance Ø0.3mm from the hole at Ø15.2mm.
If you could explain i would be very gratefull.

Thank you.

The smallest distance X occurs when you have the largest hole at lowest allowable position. I am assuming that X is located from Datum_C. This is not necessarily the same thing as the distance from the actual edge.

Note that with the hole at Ø15.2mm, your positional tolerance is Ø0.3mm.

Xmin = 30mm - 15.2mm/2 - 0.3mm/2 = 22.25mm.

Datum_C is the portion of your bottom edge that touches your fixture. This means that the maximum perpendularity error will be towards your hole. This could bring your separation down another 0.1mm.

 

[ptruitt]

The attached drawing makes sense to me.

Peter Truitt
Minnesota

 

[BLUEHONDA]

Attached is the drawing I'm working with, I'm trying to find the Max and Min for Dim (X)
My Drawing could somebody explain step by step the procedure I need to go through to find the Min and Max, like I said im a new to this game so explanation for dummies please.

Thanks all very much appreciated.

 

[Belanger]

Max = 4.25 and min = 3.75, because 4 ± 0.25 is the spec for dimension X given on the print!

(FYI, the 15.15 should not be basic.)

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

 

[pmarc]

bluehonda,
J-P is right. There is nothing to calculate except of taking min and max values of 4+/-0.25 dimension.

 

[BLUEHONDA]

what would be a better way to dimension this part up then? what do you suggest the 15.15 should be if not a basic dimension.
I am trying to maintain the hole position in relation to the edge of the plate.
Also doesnt the geometrical tolerance (Hole position Ø 0.25)have any impact on dimension (X)?
Would it be better to dimension the edge of the plate to the arc of the hole?