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Wrong diameters reported

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By [Br...] ,
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[Br...]

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So as you can see in my picture below, Calypso believes this diameter to be nearly .500" big. That is not the case I've checked it on our other smaller CMM's and I know it is within the dimension.

Now this is the 3rd time I have encountered something like this where a big diameter part that I check with Calypso and it will tell me that it is VERY far off. Also, it was similar to this part where I only have a small portion of the whole diameter. This is also exactly the way my customer wants this part checked because it is how they check it at their facility.

I heard somewhere that it may be a "curve software" option that I do not have and that is why when I try to check diameters like this that Calypso can't compute the correct diameter. Is that true, or does anyone else have any idea of what this could be?

Thanks in advance!

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[Ow...]

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The attached often helps explain why you're getting the wrong results and works in getting CMMs to spit out the numbers you want. However, it doesn't accurately represent size or position without other known features or artifacts being used to verify, for which depending on the tolerance, you may not need.

(1) Measure it with single points if possible because scanning small radius's causes some bogus points at the beginning and end of the scan.
(2) Constrain the radius to measure and report the location.
(3) Constrain the location to measure and report the radius.

Small Radius limitiations on a CMM.pptx

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[Jo...]

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For sure !
In a case like this, you are trying to take a small chord length and extrapolate radius and projected center from that. It makes more practical sense when a part like this has a theo center denoted and you can use "radius measurement" to report distances from a known point (reference a feature or alignment). You can then filter out a max/min radial distance and report those.
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[Br...]

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I am measuring with single points currently, but in the slideshow I could not play the videos. How do I constrain the radius and location?
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[Ri...]

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The best analogy I have for these measurements is to go outside and measure the circumference of the earth from your parking lot. You will get a result, but it won't be a very good one.
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[No...]

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An extreme example I often used with our engineers to explain why such measurements are very unreliable if you don't constrain:

The granite table of your CMM is supposed to be flat. But it isn't entirely because of gravity. Now, is it convex or concave? Try to measure it by scanning the entire length as a circle (yeah, let's forget about CAA for now). Measure more than once. With different point densities. Compare the results. Especially the position of the center.

The same is happening in your measurement, only the effect is not as extreme and the center won't jump up and down because the curvature is defined well enough.
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[Jo...]

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Constraining the center point should come with a warning imo . It is making the assumption, that the center is exactly where it is supposed to be from the current alignment.. What that really does is give you the average radial distance. If your print defines the center from another feature, that would be my preference. For example, if a pipe had to fit at a known x,y location, would it nest inside that radius ? All "radius measurement" does, is list every point from the center. You can mask all those and only report min and max result. Even a perfect radius will show deviations if not aligned perfect as well.
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I am measuring with single points currently, but in the slideshow I could not play the videos. How do I constrain the radius and location?
[/quote]

164_58ed2f5f0f4289e13eb245a67d25151f.jpg
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[Br...]

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Okay, thanks guys the constraints helped out so I understand it better now.

ALSO, does anyone know if it is possible to have each individual point that I have on the original attachment show up on the end report??
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[SH...]

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How does gravity causes curvature to the granite table?,Newton discovered gravity,he told it is force to centre of earth. Einstein defined gravity and told gravity is a curvature in space and time co-ordinate. Granite table is supposed to be rigid and gravity act uniformly every particle of the granite .... In Newtonian physics it should be flat....
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I agree there will be a curvature but it might be due manufacturing difficulties or other metallurgical problems. In my knowledge gravity do nothing with it.
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Only if the earth is flat too 🤣 🤣 😱
(yeah, I see the flaw in this argument - the CMM portal will follow the curvature caused by the earth and not notice it - but hey, it's just an example, ok. Let's not take this too far 🙄 )

Add yes, it also has to do with the table support. Imagine we replace the granite with a mattress of the same size. According to your reasoning it should be flat too. 🤠
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https://youtu.be/rcNP7E_5Ung
Please watch the attached video,in that video feather moves in a vertical direction without air only gravity acting second case, according to your explanation the feather should be horizontal instead of vertical.So, gravity don't bend objects....
... Gravity acting through the centre of the mass of the object, it attracted towards the centre of the earth, it (gravity)independent upon geometry of the object.
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[Ma...]

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Perhaps we should consider Norbert's example but instead of gravity, we have a significant temperature differential between the top and bottom of the granite table. If the top is warmer the surface becomes convex, if the bottom is warmer the surface becomes concave. Now who wants to try and use their CMM to determine the diameter and location of this section of this sphere? 😃
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Seriously, you should read more Einstein and less Newton 😕
What you've linked to is a free-fall experiment in a vacuum. All it shows is that the behavior of a free-falling object in a vacuum is equivalent to the behavior of the same object at zero gravity (and that the mass of the object doesn't matter). So arguing about a matter of gravity by citing a zero-gravity demonstration somehow misses the point, don't you think?
And belive me, gravity does bend objects, or at least the space-time they're in, but that's a different matter....

And now, before somebody starts to fill this thread with Einstein tensors, can we all please calm down again?
I know homeoffice puts a strain on the brain, but let's pull ourselves together and return to topic, okay? 🤣 🤣
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Sorry to say that that was not zero gravity experiment, free falling is a situation in which only gravity act no other forces...ok I stop here.....
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Sorry for breaking my words, can't became silent after seeing this like statement.

We have four fundamental forces ;gravity, magnetic, strong force,weak force.

But,still NASA using Newtonian physics for 98% it's(NASA) calculations.
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[Ri...]

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Newtonian physics, yes - Newtonian gravity, no.

If there is one flaw in General Relativity, then the whole theory is wrong, but so far they have been unable to disprove it. In addition, it was reaffirmed as not being a force with the discovery of gravitational waves which would not be a result of Newtonian gravity, but a result of General Relativity.

In addition, Newton's physics worked well for small objects, and localized science, but does not work on the grand scale of things.
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