Circular runout control; understanding potential surface effects

[dtmbiz]

Would anyone like to comment on the following?


Would the following be accurate in understanding the potential surface effects for a cylindrical feature as a result of only a circular runout control?


1. A circular runout tolerance does not need to be less than the dimensional size limits.

True?


2. Surface elements can have “steps” along the cylindrical feature axis as a result of the feature’s actual size, which may have varying circular element diameters, along with those circular element center points being displaced within the allowed circular runout tolerance.

For example, a 1.0” dia. ±.02” external cylinder with a circular run out control of .02”, could be produced within size limits and the .02”runout control, yet still allow “surface steps” as much as .04”.

True?




3. Whereas, a total runout control of .02” for the feature would only allow maximum surface element deviation of .02” regardless of the feature’s size limits.

True?

 

[Belanger]

Man, this is like peeling an onion!
For one thing, A.6.5 of the appendix seems to say that the term "true geometric counterpart" was nixed in the standard as of 2009. Yet they still use it in para. 4.6.15, and also parenthetically in 3.3.3. (Maybe in some figures too, but my search function only looks at the text.)

I guess you make a good case, dtmbiz, for the angle of the indicator on a cone of 46º +1º/-3º to be different from that used on a cone of 45º ±1º. Interesting to see what others think.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[pmarc]

dtmbiz,

Apologies for this, but I have to repeat my question:
At what angle would you set up the indicator for runout verification if the angular dimension for cone in fig. 9-2 was expressed as 43°-47°?

 

[dtmbiz]

John-Paul,

I like onions dont you? Good source of antioxidants

Anyway, the more I exercise my interpretation of the standard with you folks, the more I learn how others interpret...ultimately helping me and hopefully others to understand the concepts and the practical considerations necessary.

I taveled home for the weekend (work out of town) and didnt get the chance to offer my thanks for thanksgiving for this forum and you folks that participate!!

Very very valuable resource and I really appreciate you John-Paul and the rest of you guys and (gals?)that take your valuable time to participate! It's a great place to get various points of view, deeper understanding, correction and affirmation.
Thank you all very much.

 

[dtmbiz]

pmarc,
Definitely like the question.

45°

Considering the standard’s concept to accept as many functional parts as possible, it is most probable that I would be accepting as many parts as possible.

As in my earlier comments I mention what was the angle that was modeled or drawn. Someone chose an angle. What is it? Why? You want me to make the call? It’s 45°.

In this case let’s say that I had a $50,000 part and it failed inspection at the 45 indicator setting and then I find out with further inspection that it passes with a 43° indicator setting, there is a discussion with the responsible parties involved. The important part is that the part functions as designed and the responsible parties would need to make that decision. The part is accepted or rejected on that decision.

I believe I see your point and would ask why would limit dimensioning be used in light of the ambiguity that it causes in this instance? Engineering / Designers are supposed to apply the standard to provide design intent. As you have pointed out with your question, I don’t see limit dimensioning capturing that philosophy in this case. I personally limit, limit dimensioning Don’t particularly like it for this reason. Baseline dimensioning is legal in the standard also; however I am not an advocate for it. IMO it does not capture design intent either. As we know there are always questions surrounding application of the standard, and it does not give us the “best practices” within it.

I find that comes from on the job training....experience.
IMO and learning; ASME Y14.5m is a language to express relationship and function for communication of design intent. It is not an answer to eliminate the design process... particularly the human element. Other communication in various forms will always be needed to support engineering drawings.

Your question can be argued from various points of view. Because those arguments are note worthy, it doesn’t stop me from using runout controls on a cone because there can be a question as to what angle the dial indicator should be used to set. If the control is needed then figure out the best way for your organization to communicate “what means what to who”, regarding the runout control. Liven up your day and bring it up in your design reviews.

 

[MechNorth]

That is a good example of problems with limit-based tolerances. As written, there is no guidance as to the preferred value unless there is a note such as "UNLESS OTHERWISE NOTED, GEOMETRIES MODELLED AT MEDIAN NOMINAL".

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[axym]

Jim,

If the conical feature with the directly toleranced angle had a Surface Profile characteristic, would this be legal in your opinion? Would it make any difference if it was a plus/minus tolerance or a limit tolerance?

I'm thinking that your answer to both questions is no, but I'm not 100% sure.

Also, what's your opinion on the use of profile tolerances in conjunction with plus/minus tolerances in other contexts? Y14.5 has several figures that show this and they have always been a pet peeve of mine, particularly the one in which Surface Profile is combined with a plus/minus size dimension to control "conicity". What do you think of those?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[dtmbiz]

axym,

Not sure of your proposed scenario. I am working to the 1994 standard. It says that a profile tolerance is a uniform boundary and if you have a plus/minus angle dimension that has a "pie" shaped tolerance zone, then I cant see how that could work at all.

Fig 6-18 shows a plus/minus dimension that appears to be the min/max height of the profile. The profile tolerance is within in that range. It still has a uniform boundary.

6.5 of the standard states...

..... With profile tolerancing, the true profile
may be defined by basic radii, basic angular dimensions,
basic coordinate dimensions, basic size dimensions,
undimensioned drawings, or formulas....

According to this the profile always needs to be defined with basic dimensions. I dont see how your scenario could be "legal".

 

[Belanger]

Evan, I'll let Jim chime in, but recall how much buzz that caused in a past thread a few months ago. I used to be pretty vehement that a ± tol on a cone is never allowed if profile was to be used (because profile must be used on true profile with basic dims). But the discussion brought to light that this is sometimes possible -- ONLY in the case of a cone and if no longitudinal datum is given -- because the cone could be a perfect size and shape, but if it shifts left/right then the diameter at any given point would change.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[MechNorth]

There was a statement that I recall in '94 (sorry, don't recall where exactly) indicating that when profile is applied to a feature whose size is controlled with a limit based dimension, the profile can control location, orientation and form, but not size. So, in the case of a cone, the profile control wouldn't limit the size but would effectively control the runout (circular and total) and "conicity" of the cone. I don't see any difference between +/- and limit tolerances in this situation. On the otherhand, I don't use nor advocate the use of all "options" provided in the standard. When I teach, I explain the issue with wedge-shaped tolerance zones to my students and they balk at the concept and readily step away from +/- angular tolerances. I also teach them that optics & acoustics are probably the only two situations that I use +/- angles. The better way, in most cases, is to use basic dimensions and profile.
As for the tolerance zone description of uniform or wedge shaped, consider this; the profile control would be uniformly offset from the wedge shaped zone established by the +/- angular tolerance, resulting in another wedge shaped zone.

One other point; when using +/- angular tolerances, you need to us a dimension origin symbol or other indication to establish where the inflection point of the tolerance zone is. A minor, but critical addition to the drawing.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com