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?
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?
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Basic locating angle without FCF, yes/no?
Chris
SolidWorks 09 SP4.1
ctopher's home
SolidWorks Legion
RE: Basic locating angle without FCF, yes/no?
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.
RE: Basic locating angle without FCF, yes/no?
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.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic locating angle without FCF, yes/no?
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?
As it now stands, the drawing is not correct.
Dave D.
www.qmsi.ca
RE: Basic locating angle without FCF, yes/no?
"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 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.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic locating angle without FCF, yes/no?
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Basic locating angle without FCF, yes/no?
"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?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic locating angle without FCF, yes/no?
RE: Basic locating angle without FCF, yes/no?
John-Paul Belanger
Certified Sr. GD&T Professional
http://www.gdtseminars.com
RE: Basic locating angle without FCF, yes/no?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic locating angle without FCF, yes/no?
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?
John-Paul Belanger
Certified Sr. GD&T Professional
http://www.gdtseminars.com
RE: Basic locating angle without FCF, yes/no?
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?
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.
RE: Basic locating angle without FCF, yes/no?
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.
RE: Basic locating angle without FCF, yes/no?
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?
John-Paul Belanger
Certified Sr. GD&T Professional
http://www.gdtseminars.com
RE: Basic locating angle without FCF, yes/no?
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.
RE: Basic locating angle without FCF, yes/no?
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?
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?
Excluding less than 180 still doesn't sit quite right with me though.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic locating angle without FCF, yes/no?
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?
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?
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?
Frank