Basic locating angle without FCF, yes/no?

[cwdaniel]

See attached drawing for reference. (assume this is in a drawing with title block tolerance and all other features properly defined)

A colleague asserts that this is acceptable, making the angle basic and nothing else. Plus no FCF controlling location. I'm not sure of the reasoning behind this either.

I'm thinking no, until reading Y-14.5m 1994 1.3.9 and looking at figs 2-14 and 2-15 referenced there. Now I'm not so sure.

What say you guys?

 

[ewh]

While the subject of established tooling or gaging tolerances has been recently mentioned, I don't think that would apply in your situation, unless your example is that of a tooling fixture. If not, the basic angles are essentially meaningless as shown.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[ctopher]

I agree with ewh. More info is needed on the drawing.

Chris
SolidWorks 09 SP4.1
ctopher's home
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[drawoh]

cwdaniel,

Perhaps your colleague is assuming that the radii must fit within a tolerance zone centred exactly on the nominal position. This is a composite of positional error and radius error. Do the math and figure out just what these errors look like. They can be surprisingly small.

I like to apply zero positional tolerances at MMC on holes, but I make the diameter specification sloppy.

If it were my drawing, I would apply a positional and diameter tolerance, or a profile tolerance.

JHG

 

[KENAT]

Unless perhaps there's some title block tolerance for hole/radial feature position tolerance or something (which itself might be dubious) then what you show doesn't look correct.

In the example figures you site the tolerance comes from the tolerance on the intersect point of the line which in turn gives you a tolerance zone. This, or similar, is usually the case too with gaging tolerances ewh mentions I believe.

In you drawing this doesn't appear to be applicable.

Essentially on the rare occasions you use a basic dimension without FCF the resulting feature must still have some kind of tolerance on it, though it may come from tolerances on other dimensions that define its size/location.

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[pmarc]

drawoh,

I think profile tolerance would be much better since a positional tolerance cannot be aplied to non-feature of size.

 

[dingy2]

One cannot use a positional tolerance here since it is not a feature of size. Profile of a surface (or line) FCF should be added to this drawing.

As it now stands, the drawing is not correct.

Dave D.

http://www.qmsi.ca

 

[ewh]

I am confused, so bear with me... Why isn't a radius considered a feature of size?

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[KENAT]

ewh, we had this argument here some time ago. Many claim that if you can't put calipers across it, then it's not a feature of size.

That's not my interpretation of 1.3.17, a portion of a radius is still a cylindrical surface to my understanding and the 'caliper test' is an or not an and.

1.3.17 Feature of Size. One cylindrical or spherical surface, or a set of two opposed elements or opposed parallel surface, associate with a size dimension.

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[ewh]

Thanks, KENAT. Now I remember that thread, and I still agree with your interpretation. The radius is a cylindrical surface. It may not be conducive to inspection with calipers, but it is what it is. I guess I'm not going crazy after all.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[dingy2]

Feature of Size - ASME Y14.5M-94 1.3.32.1

"One cylindrical or spherical surface, or a set of two opposed elements or opposed parallel surface, associate with a size dimension."

The 2009 edition is a bit more explicit but in any event a partial diameter would not fit this criteria unless it was a semi-circle where one could actual measure across the diameter.

In the case shown in the sktetch, we appear to have some scallops or maybe we can call them quarter circles. How don't know how this fits the criteria for a feature of size?

In the above situation, profile of either a line or surface is more appropriate.



Dave D.

http://www.qmsi.ca

 

[KENAT]

I don't know about 2009, but I don't see the requirment for the cylindrical surface to be 180° or more? The opposed elements/surfaces are 'ors' not 'ands'.

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[SDETERS]

Maybe what the colleague is trying to say hey it is 8X so the features need to be clocked and evenly spaced. I almost see that this dimension is put on the drawing as a reference dimension. Saying yes these features are evenly spaced and at 45 degree angles. Now the drawing how it is dimensioned is not correct per the standards. Plus there is no tolerance specified this angle and the clocking of the pattern. Look at fig 5-2 in the Y-14.5m 1994 standard

 

[Belanger]

If a radius qualifies as a "cylindrical surface," then would you guys say that an arc is the same thing as a circle? (!)




John-Paul Belanger
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[KENAT]

Isn't that what's being questioned? Does it have to be a complete cylinder to be considered a 'cylindrical surface' or is a portion of a cylinder still a 'cylindrical surface'?

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[cwdaniel]

To redirect the conversation away from a "what constitutes a feature of size" debate. The question at hand is more to the use of the basic dimension rather than leaving just a +/- dimension like the other ones involved. The function of these scallops/divots/notches is easily met with using the +/- diameter/angle/radial size callouts.

If the requirement was different, then I would consider using the appropriate basic dims and GD&T. Position, profile whatever.

I think the colleague may think the basic angle is appropriate because radii centers are "off the part".

Not sure though because I haven't been able to finish the discussion with him yet.

At this point I'm standing on my original assertion that the basic angle should not be there.

 

[Belanger]

I guess I'm saying that a circle is by definition a complete shape. A cylinder is just that -- a cylinder. If you have a radius, it's a portion of a cylinder. So no dice when it comes to the definition given by ASME for a feature of size.


John-Paul Belanger
Certified Sr. GD&T Professional

http://www.gdtseminars.com

 

[Belanger]

Thanks for bringing us back on track
Yes, as it is the basic dimension is not appropriate. Even if the centers of the radii are off the part, the angle speaks to where those radii will be. So I agree with your original assessment.

John-Paul Belanger
Certified Sr. GD&T Professional

http://www.gdtseminars.com

 

[drawoh]

dingy2,

A radius can be tested with go-no-go gauges. A design requiring an accurate radius and allowing sloppy location is not likely, but it is possible.

JHG

 

[drawoh]

cwdaniel,

The location of the radius centres on or off the part is irrelevant to whether or not to use basic dimensions.

We do not know what your part does. Probably the best dimensioning scheme would be to make the radius basic as well, then apply a profile tolerance to it. If an inspector has to figure out where the centre of his gauge is, as I note above, he is going to hate you.

As far as I know, all the equally space angle examples in ASME Y14.5 are shown as an explicit angle and a quantity. Calling out the angle is correct.

JHG