Giving Radii a running start.

[[An...]]

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"Tangent" is not a criterion,and in reality,there is no "banana shaped" tolerance zone.
What we see here, are two formerly concentric tolerance circles that are shifted in order
to illustrate an actual profile that lies within the tolerance without having any offset
to the adjacent geometries.
It's simply a graphical thing.
In reality there is no adjacent plane that is perfectly tangent to a cylinder!

Checking small arcs only works well if you use 2D curve and profile.
The number of the nominal points is equal to the number of actual points.
The evaluation is: distance of two "opposed" points

[[Br...]]

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Yes there could be variation between the individual points where some fall inside the tolerance zone and some outside. But If you use the "Radius Measurement" Characteristic (not "Radius") it looks at each point individually. Unfortunately you don't get the Banana shape zone with this method, but it is still closer to the true tolerance zone than if you don't constrain the center point. Remember if you don't constrain the center-point, its still using least squared(assuming that's the fitting algorithm you use), plus its projecting the missing portion of the circle to create a center point.

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The tolerance zone, if no center-point is dimensioned, is absolutely tangent to the adjacent edges. It's theoretical so it can be perfectly tangent. And it is banana shaped. That pic i posted is straight out of Y14.5 and it shows the tolerance zone clear as day. It refers to it as crescent shaped.(I guess banana sounded to silly for those fellas.) In these cases its the edges that control the location of the radus, not a dimension to the center point. It all depends on how its drawn.

ASME Y14.5-2009 Para. 1.8.2.1
Center of Radius.
Where a dimension is given to the center of a radius, a small cross is drawn at the center. Extension lines and dimension lines are used to locate the center. See Fig. 1-23. Where location of the center is unimportant, the drawing must clearly show that the arc location is controlled by other dimensioned features such as tangent surfaces. See Fig. 1-24.

Para 1.8.5
Rounded Corners
Where corners are rounded, dimensions define the
edges, and the arcs are tangent. See Fig. 1-31.

[[Cl...]]

Here's an old school way of measuring a very small radius segment.
Get the intersects (tangents of each side of the radius) Create a
mid-point from them, make that X zero.

Probe a point on the radius at X zero, make that X zero. Now translate
back the nominal radius and switch to polar. take hits on the radius.
Please excuse the crude sketch.

[attachment=0]SR.png[/attachment

SR.png

[[An...]]

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Decades ago I learned,that all surface points have to lie within the DASHED ZONE.
And I also learned that the form of a shape does not automatically decrease
when the points are located near the adjacent surfaces.

So,what is the topic here?

Points within a dashed zone?

Derived elements within numerical limits?


See attached.

Fillet_Radius_2.pdf

[[Br...]]

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Ok so the machinists you work with can't make fillets for some reason. That's not the same thing as what you said earlier. You said there is no Banana shaped tolerance zone. But if you stipulate on your drawing that the standard is to comply with Y14.5, then there is a Banana shaped tolerance zone.

[[Aa...]]

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Interesting. I've never noticed the "Radius Measurement" characteristic, nor did they point it out in basic training when we covered this subject.

If it looks at each point individually, and you have the position constrained, then it's essentially a profile tolerance.

What's often overlooked, though, is that following the "banana tolerance" prescription in Y14.5, the width of the tolerance zone, even at its widest point, is only a fraction of the stated radius size tolerance. This depends on the arc angle, but at 90 degrees, it's 41.4%, at 60 degrees, it's 15.4%, and at 45 degrees it's only 8.2%!

[[Br...]]

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Yep, but so is the radius' tolerance zone. That's why I mentioned before its closer to a profile tolerance zone than a size tolerance. This is really important to understand especially when distinguishing between features of size, and non features of size. Applying a position tolerance to a radii would be a mistake for this reason.

[[Aa...]]

That's great, but simply applying a "Radius Measurement" characteristic with constrained position would establish a profile band of a width equal to the radius tolerance, which as I said, is not the width of the profile band in Y14.5.

[[Br...]]

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Unfortunately, but it's closer than just doing a regular radius without constraints in my opinion.

[[An...]]

Radius,2D Curve,Evaluation strategy.
See attached.

Fillet_Radius_1.pdf