doubt about perpendicularity in diameter application. 1

[Vimalmechs]

Hi,
I got a doubt in between learning tolerance stack.I am trying to convert the dimension to dimension with equal bilateral tolerance.please refer the dimension located at square one in image. The output is 30+/_.03 or 30+/_.10 ?
Vimal.V.V.

 

[KENAT]

What am I missing here?

How can we tell you what the correct out put is when you don't appear to give input?

Posting guidelines faq731-376

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

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

 

[pmarc]

There is nothing to convert.

If we are talking about the requirements applied to the cylinder, 3 separate conditions have to be satisfied:
1. Each actual local (two point) size measurement has to be within 29.97-30.03.
2. The cylinder must not violate unrelated actual mating envelope (UAME) of dia. 30.03. This envelope is defined by Rule #1 and is not related to any datums.
3. The cylinder must not violate related actual mating envelope (RAME) of dia. 30.07 (30.03+.04). This envelope (also called the Virtual Condition) is perfectly perpendicular to datum plane A.

 

[Vimalmechs]

Kenat, what is missing in input ?.

Pmark, I am talking about RAME.the below is right based on RAME ?
Virtual condition= 30+.03+.04
Resultant condition (worst inner boundary) = 30-.03-.04-.06

Vimal

 

[pmarc]

Vimal,

If this was the point of your question, it looks like you have already answered it by yourself - neither 30+/_.03 nor 30+/_.10 is the correct output. VC=30.07, RC=29.87, so the answer is rather 29.97+/-.10.

I just still think it is a bad idea to do the conversion (not to mention that I hardly see a benefit behind it). Reason? Unlike the Virtual Condition, which is constant boundary regardless of size of the cylinder's UAME, the Resultant Condition boundary = 29.87 is valid only for UAME = 29.97. If size of UAME is greater than 29.97, size of RC boundary changes (gets bigger). In other words, the RC boundary is not a constant value, thus the output you are looking for shouldn't really be a single expression, like 29.97+/-.10, too.

 

[Vimalmechs]

Pmarc,

I am learning Worst Case tolerance stack up. That is the reason i am looking for "30-.03-.04-.06= worst inner boundary" instead of any other value.

 

[pmarc]

Vimal,
I understand you are searching for worst-case values.
My question would be what kind of stack up is this? What are you exactly trying to calculate?

I am asking, because I just can't imagine a tolerance stack that would require expressing VC and RC values in the xxx+/-yyy manner.

 

[Vimalmechs]

Pmarc,
Am trying to calculate the overall dimension as per fig. Square 2 is th FCF am concerned.

 

[pmarc]

Vimal,
Your case does not require expressing VC and RC size values in the xxx+/-yyy manner. In fact your stack(s) should not take the RC size into account at all.

Assuming you are searching for MIN and MAX "Overall" distance, here is one of the ways to think about it:

1. MAX possible "Overall" is when:
a. Size of RAME of datum feature B is 49.97 (the feature's UAME is at LMC size and its axis is perfectly perpendicular to datum plane A);
b. Size of RAME of datum feature D is 50.10 (the feature's UAME is at LMC size and its axis is perfectly perpendicular to datum plane C);
c. The larger cylinder in the male part is at its MMC size = 100.2, and its axis is off the datum axis B by half of the runout tolerance, that is 0.05 in one direction (up or down);
d. The outer cylinder in the female part is at its MMC size = 100.2 and its axis is off the datum axis D by half of the runout tolerance, that is 0.05 in the opposite direction.
Regardless of a stack template you are using, the RC size values for datum features B (49.91) and D (50.17) will not show up in the calculations.

So the answer for "Overall" MAX is: 100.365.

---
2. MIN possible "Overall" is when:
a. There is no loose between RAMEs of datum features B and D, meaning that their size is 50.03;
b. Both outer cylinders, in the male and the female part, are at their LMC size = 99.8, and the cylinders are perfectly coaxial with corresponding datum axes.

In this case everything is perfectly aligned and centered, so the answer for "Overall" MIN is simply 99.8. Notice that yet again the RC size values for datum features B and D have not been considered in the calculations.

 

[Vimalmechs]

Hi Pmarc,

Thank you for the detail explanation.

Pmarc, please refer the attachment. I am just clarifying my understanding. red dash lines are tol zone, and green are axis of feature of size.At feature MMC, the axis can tilt with in dia 2 tol zone as per square 1 and 2. And square 3 is wrong.Is it ?

 

[pmarc]

Vimal,
Why 3 is wrong? Axis is perpendicular to datum plane A, so how can it be wrong?