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Basic locating angle without FCF, yes/no?

Basic locating angle without FCF, yes/no?

Basic locating angle without FCF, yes/no?

(OP)
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?

RE: Basic locating angle without FCF, yes/no?

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." - Robert Hunter
 

RE: Basic locating angle without FCF, yes/no?

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

Chris
SolidWorks 09 SP4.1
ctopher's home
SolidWorks Legion

RE: Basic locating angle without FCF, yes/no?

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

RE: Basic locating angle without FCF, yes/no?

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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RE: Basic locating angle without FCF, yes/no?

drawoh,

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

 

RE: Basic locating angle without FCF, yes/no?

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.
www.qmsi.ca

RE: Basic locating angle without FCF, yes/no?

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." - Robert Hunter
 

RE: Basic locating angle without FCF, yes/no?

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.

Quote (ASME Y14.5M-1994):

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.


Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
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RE: Basic locating angle without FCF, yes/no?

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." - Robert Hunter
 

RE: Basic locating angle without FCF, yes/no?

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.
www.qmsi.ca

RE: Basic locating angle without FCF, yes/no?

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

RE: Basic locating angle without FCF, yes/no?

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
Certified Sr. GD&T Professional
http://www.gdtseminars.com

RE: Basic locating angle without FCF, yes/no?

(OP)
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.

RE: Basic locating angle without FCF, yes/no?

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

RE: Basic locating angle without FCF, yes/no?

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

RE: Basic locating angle without FCF, yes/no?

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

RE: Basic locating angle without FCF, yes/no?

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

RE: Basic locating angle without FCF, yes/no?

Sorry, but this still bothers me...
If you hve a "cylindrical" surface that encompasses, say 270° and can be inspected using calipers, it would be a considered feature of size?  But if it only encompassed 179° it would not?  If the smaller surface cannot be considered cylindrical in nature, how can the larger?

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

RE: Basic locating angle without FCF, yes/no?

That's right.  Going below 179.999 degrees makes it a non-FOS.  Because to measure a size, you have to have something to measure, right?  And the way ASME defines size is the straight-across distance between to opposing points.

John-Paul Belanger
Certified Sr. GD&T Professional
http://www.gdtseminars.com

RE: Basic locating angle without FCF, yes/no?

ewh,

   I just created this part for an imaginary requirement.  It would sit between five Ø30+0/-0.1mm pins located within Ø0.2mm.  I forgot to indicate the quantity of radii.  I should have entered 5X R15.3/15.1.  

   A unilateral profile tolerance would work here.  If I changed the positional tolerance to something like Ø0.5, with or without MMC, the profile tolerance would not work.  I cannot conceive of a design requirement that would make me do this.   

               JHG

RE: Basic locating angle without FCF, yes/no?

drawoh:

The plug gauge that you described on a radius is the inner boundary of a profile of a surface. It really doesn't check if the profile is beyond the outer boundary just inner one.

ewh:

The larger cylindrical surface encompassing 270 degrees can have the diameter measured with a vernier calipers and could be considered a feature of size while a less than a semi-circle (less than 180) cannot. It does not have 2 opposed elements that can be measured.

2009 ASME 1.3.32.1

"Regular feature of size: one cylindrical or spherical surface, a circular element, and a set of two opposed parallel elements or opposed parallel surfaces, each of which is associated with a directly toleranced dimension. see para 2.2"

Para 2.2 Direct Tolerancing Methods

(a)  limit dimensioning -  high & low
(b)  Plus and Minus Tolerancing
(c)  Geometrical Tolerances Directly applied to features

Dave D.
www.qmsi.ca

RE: Basic locating angle without FCF, yes/no?

But where does it specify that less than 180° is not to be considered a cylindrical surface but greater than 180° is?  I do undertstand the inclusion of the two opposed parallel elements, but not the definition of "cylindrical" as used here.
There do actually exist inspection methods which can ascertain the same information from a partial "cylindrical" surface as from an complete surface.
Same argument can be used regarding arcs/circles.  All of the information contained in a circle can be ascertained from an arc.
What about "Irregular Features of Size"?

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

RE: Basic locating angle without FCF, yes/no?

ewh, (and at the risk of annoying the OP and going further on the tangent) There argument that a portion of a cylinder over 180° is I think based not on the fact that is' a 'cynlindrical surface' but that it has opposable points.

Excluding less than 180 still doesn't sit quite right with me though.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Basic locating angle without FCF, yes/no?

(OP)
No annoyance here! I think I got my consensus evidence for my needs. Any other discussion is enlightening, or at the very least entertaining. I seem to stir up this kind of stuff on the rare occasion that I post here.

And for drawoh, actually I'm the inspector too. Real small operation here. Designers are the inspectors, and with limited tools. Low production ones and twos don't warrant any sort of go/no go gauges for a specific part.

The reality of that inspection will probably be a combination of math and calipers across two opposing radii. Plus a laser cut 1:1 2D template to verify. Finally, does it fit when I/we put it together?  

RE: Basic locating angle without FCF, yes/no?

Hi cwdaniel

If its a basic dimension then it needs a position tolerance relating to the centre of the radius.
Unless there is something else on the drawing which we haven't seen as yet, in terms of tolerance, how does one ensure the position of eight radial centres with zero error?

desertfox

RE: Basic locating angle without FCF, yes/no?

KENAT and ewh, please, stick to your guns.
I don't think it smells right either. I think the people who sell GD&T have taken over the committee and are trying to make it more palitable for the non-believers. If I dimension something as a radius it can't be a feature of size but if I dimension it as a diameter I can? The feature hasn't changed.
Like the straightness vs flatness for exemption of perfect form at MMC on non-cylindrical features. Logic is finally winning out.
Sorry to preempt again.

KENAT please point me to that thread.

RE: Basic locating angle without FCF, yes/no?

Back to OP, by my reading, I would say the standard actually does not require the use of position tolerancing or profile tolerancing to use a basic dimension it can be mixed with plus or minus dimensions as is shown in the standard itself, see definition: DIMENSION,BASIC. I also see no "feature of size" radius exclusion then, either. So I do not think referencing the standard is the way to shoot this one down, So I say: "YES".
Frank

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