## Tolerance Stack Question

## Tolerance Stack Question

(OP)

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?

## RE: Tolerance Stack Question

## RE: Tolerance Stack Question

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

Chris

SolidWorks 10 SP4.0

ctopher's home

SolidWorks Legion

## RE: Tolerance Stack Question

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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## RE: Tolerance Stack Question

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.

## RE: Tolerance Stack Question

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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## RE: Tolerance Stack Question

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

towardsyour hole. This could bring your separation down another 0.1mm.JHG

## RE: Tolerance Stack Question

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

## RE: Tolerance Stack Question

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

## RE: Tolerance Stack Question

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

## RE: Tolerance Stack Question

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

max value: 22.55

## RE: Tolerance Stack Question

John-Paul Belanger

Certified Sr. GD&T Professional

Geometric Learning Systems

## RE: Tolerance Stack Question

SeasonLee

## RE: Tolerance Stack Question

John-Paul Belanger

Certified Sr. GD&T Professional

Geometric Learning Systems

## RE: Tolerance Stack Question

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.

## RE: Tolerance Stack Question

Peter Truitt

Minnesota

## RE: Tolerance Stack Question

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.

## RE: Tolerance Stack Question

(FYI, the 15.15 should not be basic.)

John-Paul Belanger

Certified Sr. GD&T Professional

Geometric Learning Systems

## RE: Tolerance Stack Question

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

## RE: Tolerance Stack Question

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?

## RE: Tolerance Stack Question

Consult any simple GD&T reference book/guide for an example of this scenario.

Your answer for "X" would then be a max of 4.125 and a min of 3.875, because the given geometric tolerance is diametrical (think of the tolerance zone as being centered exactly at 4.00 so it translates to .125 in any radial direction). The max distance between the holes would be 39.25 and the min would be 38.75.

John-Paul Belanger

Certified Sr. GD&T Professional

Geometric Learning Systems

## RE: Tolerance Stack Question

I do not think you want to dimension arc of the hole from the edge of the plate. In most of similar cases position tolerance is applied to control location of holes axes relative to other features.

Why the hole position (Ø 0.25) has no impact on dimension (X)? Because you directly defined that the distance between axis of left hole and left surface of the part is 4±0.25. With your dimensioning scheme position tolerance is important only when any relationship between both holes is considered.

## RE: Tolerance Stack Question

The hole has a positional tolerance of 0.1mm diameter

at maximum material condition. It applies at the minimum diameter of 15.0mm. As you increase the actual diameter, you increase the positional tolerance. At 15.2mm diameter, the positional tolerance is 0.3mm.JHG

## RE: Tolerance Stack Question

Several people have had a go at this and given me different answers.

Is there a quick and easy method of working this out? And please bare in mind that I'm very new to this stuff, so explanation for dummies please.

Thank you all.

## RE: Tolerance Stack Question

Look to attached presentation. It is showing an example of how you could have thought about the stack I asked for a double check at the very beginning of the post. I tried to explain it as simply as I could. Hope this helps.

http

P.S.: If you are asking for a quick and easy method of dealing with tolerance stacks, I would say it really depends on one's experience, preferences and how complicated a stack is. The method I like to use (it is not the one I showed in the attachment) is really easy and consistent for me, but that does not mean it would be clear for you. First of all try to do as many stacks as possible, choose different calculation methods as described in different GD&T books (e.g. Krulikowski, Fisher or other authors) and you will quickly notice which one is most suitable for you. Additional Tolerance Stack-up training would also help for sure as you you seem to be at a beginner level.

## RE: Tolerance Stack Question

SeasonLee

## RE: Tolerance Stack Question

pmarc

Am I correct understood from your PostScriptum that stackup results can be differ and it's depend from calculation methods (e.g. Krulikowski, Fisher or other authors)?

## RE: Tolerance Stack Question

John-Paul Belanger

Certified Sr. GD&T Professional

Geometric Learning Systems