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]

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." - [small]Robert Hunter[/small]

 

[Belanger]

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

 

[drawoh]

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

 

[dingy2]

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.

http://www.qmsi.ca

 

[ewh]

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." - [small]Robert Hunter[/small]

 

[KENAT]

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

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[cwdaniel]

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?

 

[desertfox]

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

 

[fsincox]

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.

 

[fsincox]

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