Confusing Line Profile Result

[[Jo...]]

Hello All,

I hope that someone can help me understand a result. I am measuring a line profile with a curve. The callout is .025" with an unequally dispose tolerance of .015 to the add mat'l side. (.025 U .015 -AB-) -AB- is fully constrained. I'm trying to understand how calypso calculates this. This is the result for the characteristic along with the min and max points:

I've been looking for how an unequally toleranced profile is supposed to be reported but have only found how to define the tolerance zones. What I think should happen would be to take the absolute value of the deviation from the side that uses the most of its tolerance, add the absolute value of the tolerance from the opposite side, and report that number. For example, for the characteristic above, the minus side is .0010" over the tolerance for that side at .0110". If you take that number and add the .0150" tolerance from the plus side, the reported number would be .0260". Why is Calypso reporting the number at .0269"? 

[[Ca...]]

Hi Joseph, 

Here's a helpful resource that will show you exactly how each of the different profile zones are calculated in CALYPSO: https://portal.zeiss.com/knowledge-base?id=415735

[[Ma...]]

Calypso doubles the largest deviation per the ISO spec. If you switch to Bilateral Two results you will see the Max and min deviations but since this doesn’t meet your requirement you may need to report out the max and min separately.

[[To...]]

Does the BETA GD&T Engine provide provide the correct solution via ASME?

Edited July 10

[[Jo...]]

Thank you

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, that explains the result. I don't really understand why it would be reported that way, but at least I understand how the calculation was made. 

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 Does that result line up with the ISO standard? I didn't mention it, but everyone seems to have realized I am working in the ASME standard. As I stated, I couldn't find anything that states how it should be reported per ASME Y14.5. My guess is that it is explained in Y14.5.1, but I don't have that standard available to me.

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 Do you know how it should be reported? I went through the example of an unequally distributed tolerance described Knowledge Base article that Caitlin provided. In each example, using the method that I described in my original post would show the true deviation from the tolerance with a single result, related to the full tolerance callout. 

[[Ri...]]

You will need to reference Y14.5.1 if you want to understand the math.

Calypso does this though:

• If it is Bilateral with equal tolerance direction, the Profile result is always whatever the largest deviation is X 2. 
• If it is Bilateral with unequal tolerance direction, the first thing Calypso does is find the tolerance nominal:
  • In your specific case, the tolerance nominal is +0.0025 above the true profile nominal
  • Now calculate what is the largest deviation from the tolerance nominal
    • In your specific case, the largest deviation is the 0.0110 deviation from the true profile nominal, which is actually 0.0135 from the tolerance nominal
  • Now multiply the largest deviation from the tolerance nominal X 2 to get your Profile result
    • In your specific case 0.0135 X 2 is 0.027 (I suspect rounding is why the result doesn't match 1:1)

Now, which one do you report to your customer, well it depends on the customer. Lol. A lot of customers would just want the Profile result, but a lot of my Aerospace customers would want both results (Profile result, as well as the Min/Max values). 

Here is a sketch. 

The black line is the true profile nominal, the red lines are the tolerance bands, and the blue line is the tolerance nominal. 

I hope this helps. 

Edited July 10

[[Jo...]]

Thank you

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 for that detailed explanation. I do now understand how Calypso is making that calculation. My question is why? I assume it aligns with the ISO standard. Again, that method of reporting a profile measurement doesn't make sense to me, but standards are what they are. Thank you everyone for your help.

[[Ri...]]

I cannot speak for the ISO standard because I don't have access to it, and honestly the ISO standard is a mess compared to the ASME standard. 

Either way - per ASME 14.5.1-2019 the math is the following:

• The actual value is t0 + 2g
  • Where t0 is the tolerance value
  • Where g is growth parameter, or essentially the distance of the actual profile to the tolerance band (this g is to be calculated from both sides of the tolerance - essentially your min/max values)
    • If the actual profile lies within the tolerance zone, the growth parameter (g) is negative. 
    • If the actual profile lies outside the tolerance zone, the growth parameter (g) is positive.
• So if your specific example, the Max deviation has a growth parameter of -0.0043, and the Min deviation has a growth parameter of +0.0010. 
  • t0 = 0.025
  • largest G is +0.0010
    • 0.025+(2*0.0010)
      • 0.025+0.0020
    • Actual value = 0.027

So is Calypso doing that? Essentially, but just in a different way. I think Calypso just takes the approach that it is easier to understand that the Profile result is always whatever the largest deviation from nominal * 2 is - the only thing to remember is that if it is a bilateral tolerance with equal distribution the nominal is the true profile, and for a bilateral tolerance with unequal distribution it is the tolerance nominal. 

Edited July 10

[[To...]]

Here's something I found that might be interesting to some.