evaluating a 45° angle between planes.

[[RP...]]

We're having some trouble agreeing on an angle result.

Depending on what the other plane is, the CMM measures the angle between 43° - 47°

I'm told by the engineer that it's actually a near-perfect 45°. 

The customer uses a 3d scanner and their results are very close to my cmm results.

Is there a super secret way to evaluate angles differently?

Here's a visualization of the chamfer's profile.  I added random datums to constrain the DoF.

 

 

 

[[Ma...]]

If it's just a chamfer, then i would stick to the closest feature to this chamfer. In other words it's local angle

If part is thin it can bend by fixture force or machined features can bend via machining forces. Then chamfer is to none machining force.

So if it's chamfer of a hole - you can compare angle to plane at hole or hole itself.

[[Ma...]]

Can we see what the callout looks like on the print?

[[RP...]]

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Here's a section view.  it's about a half inch in length.

[[Ma...]]

For me this is too small to accuratelly measure.

For 0,5mm chamfer i do only one point in the middle of chamfer.
Make intersection from faces to obtain sharp corner.
Place a touch point and direction set to 45°
From that point place theoretical 3d line and intersect from both sides. Now you can measure distance from both directions.

For our usage is this fine.

[[Ma...]]

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I wouldn't try to do a profile evaluation of it... The first feature would be the top face not any symmetry or anything like that... I would either scan a line on top face and a line on the chamfer itself with 0.010" speed and 0.0175-.020" length... Then just do "Angle Between Features" characteristic...... Have the filtering on and evals be LSQ for both features.....

[[RP...]]

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I've tried line to line angle as well, and get nearly the same thing as the plane to plane angle.

I'm having a hard time understanding the cad evaluation.  Wouldn't the shape of the angle measurement be the same as angularity?  I'm also not sure why the cad eval doesn't change color when the characteristic is out of tolerance.

I'm doing grid scans on the planes.

 

[[Ma...]]

Reason I go with line to line is to avoid as much of form error as possible.... Unless features are large enough faces to be considered planes.

If you need to continue scanning the planes, then I would make sure that your planes filter out the form errors properly as well as use LSQ eval instead of Outer Tangential.

 

For CAD Eval: Once you set it click on a different characteristic and then back on the one you wanted to look at. Also make sure that you have "color gradient" turned on.

 

Angularity itself is checking the form and orientation of the face compared to the nominal angle. It is no different than checking parallelism (form/orientation at 0°) and perpendicularity (form/orientation at 90°), everything in between those two angles falls under angularity.

 

If the callout is a simple chamfer check, then doing grid scans and checking the form/profile is probably overdoing it.... I would try to picture it as if you set the part on the comparator how would you check/verify your result and then have CMM mimic that.

[[Je...]]

Hi

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.  It looks like you've really been diligent on analyzing this problem.  I like the form plots.

Regarding your two last questions:

1. "Wouldn't the shape of the angle measurement be the same as angularity?"

That's an understandable assumption.  However, no, the shape of the scanned deviations for an angular measurement are fundamentally different from those in a GD&T angularity characteristic.

The reason for this relates to the shape of the tolerance zones.  Angularity establishes a linear tolerance zone that is controlled by a basic angle driven by the datums.  In the case of your chamfer feature, the shape of the tolerance zone is two parallel planes. The .001064 deviation is the quantity of linear deviation from the center of that coplanar tolerance zone.

Regarding colors: The magnitude (farther or closer from nominal) of deviations in the angularity characteristic will assign the color gradient based on departure from the coplanar tolerance zone.

2. "I'm also not sure why the cad eval doesn't change color when the characteristic is out of tolerance."

The way that the color gradient in Calypso angular characteristic should be assigned is in an arc-shaped path relating to the angle.  However, for angle measurement, all we get is a form plot that shows us the form deviation of the two features of interest.  This is why there is no color gradient assigned, and it's all green.  This CAD evaluation is still useful; however, because it shows you how the planes are calculated according to their form error, and significant form error can be a signal for out-of-tolerance results.

I hope that answers those two questions.  Chamfers are important features that are often downplayed as "simple."  Also, the evaluation algorithm that is assigned to each of the features that construct your chamfer is very important.  Outer tangential method will be prone to rocking the planes and introduce high variation in results.  If you're using high density scanning, which appears to be the case, LSQ may give you more stable results.  Either method may be valid, but it helps to be aware of the effects.

Chamfers are also a rare case where I sometimes enable the "constraints" options in the evaluation tab of the features to prompt the characteristic to only consider deviation along vectors that matter functionally.

I'm interested to hear how this chamfer measurement problem develops for you. 

[[RP...]]

Thank you Jeff and Marcel!  I'm very grateful for both of your responses. 

I completely agree that I'm over doing it.  Typically I would also just make line scans, since it's just an angle and length measurement, nothing to it.  I've been attempting to convince my co-workers that no matter where I take the line scan, it's not 45°.

[[RP...]]

Constraining both planes in the characteristic evaluation was my issue.  It's outputting a result that the engineer can agree with. 

Like I said, my go-to scanning methods usually work.  I've never had problems measuring angles between planes before, it's cone angles I have issues with evaluating.  I was getting the same thing on the comparator and keyence too.

The customer is still 3d scanning the feature and will probably tell us it's out.  But I did what I could.

Thanks again for all the information!

[[RP...]]

I'm lost again attempting more research.

The results are in tolerance if the angled feature is constrained, but the cad eval looks warped. 

The results are out of tolerance if neither are constrained, but the cad eval looks fine.