Controling Location of Tapered holes ?

[Madhu454]

Hello All,

Please see the attached drawing.
I need to control the location of tapered hole with respect the outer shaft diameter,

Question
1) Can I use circular runout to control this? Circular runout controls both form as well as location of each sections wrt datum A. ?
2) Can I use Position control for this?? Is it possible to use position control to locate the taper hole? Please refer to figure-3, I got confused for which dia I need to apply position control. Assume that I have used Position control for dia 20.0-20.1, how do they establish the axis? Is the AME will be a cylindrical pin or taper pin? If they use cylindrical pins will touch the part at only one point and will not get into the taper hole. The same way if I use position tolerance for smaller hole dia.

Please let me know the best method to control the location of taper hole. also please let me know whether Position control can be used for this?

Thanks for your time.

Madhusudhan Veerappa
Mechanical Engineer

 

[PaulJackson]

John-Paul
Just commenting on your last response... I have not read the rest of the thread.

When profile controls size as well as and form, orientation, and/or location it can be thought of as a control that the tolerance is both "zero at MMC" and "zero at LMC"... giving the feature its greatest freedom to rotate and translate at the profile's median contour.

Paul

 

[Belanger]

I agree, Paul. But for Evan's point, I think we can still say that the size variation provided by the profile control factors into the position tolerance, and provides bonus.

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

 

[Belanger]

Whoops, check that -- I see what you mean, Paul. If a cylinder/cone is at its biggest, it can't move; but if it's at its smallest, it also can't move.

I'll have to noodle this idea, but I still refer Evan to Fig. 8-24 where ASME shows a similar concept.

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

 

[Belanger]

PrDave ... good point about Fig. 8-17. That's been the subject of several forum discussions, and I'm not the only one who thinks that example is a little strange.

I only say this because paragraph 8.2 says that a profile tolerance defines a tolerance zone "relative to a true profile." The same paragraph defines a true profile as "a profile defined by basic radii, basic angular dimensions, basic coordinate dimensions, basic size dimensions, undimensioned drawings, formulas, or mathematical data, including design models."

Figure 8-17 has a basic angular dimension, so I get how the profile tolerance controls the angle of taper. But don't they need a basic dimension for the diameter? Otherwise, it's not really controlling profile in the round aspect of the cone, and profile of a line might be more appropriate.


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

 

[SeasonLee]

madhu454

The geometric tolerance should be less than the size tolerance on your latest post fig.1 and fig.2, take fig.1 for example: the surface profile tolerance 0.5 is greater than the size tolerance 0.2 (10.2 – 10.0), it’s a conflict.


SeasonLee

 

[SeasonLee]

madhu454

Quote from Al Neumann GD&T workbook page 12.3 :
“Profile tolerance is also very versatile. The classic profile specification is usually applied with datums and basic dimensions. But profile can also be applied with plus/minus tolerances. If it s applied with plus/minus tolerances, depending on the situation, it will react like a form or orientation tolerance and must be within the confines of the plus/minus tolerance.”

On a flat feature, surface profile tolerance zone is two parallel planes equally displaced about the true profile, the surface must lie within these two parallel planes, in other words, the surface variation is controlled by these two parallel planes, so surface profile will also control the flatness, this is same as surface parallelism will also control surface flatness.

SeasonLee

 

[Belanger]

Sorry to keep pushing the point, but now that I'm at home I am able to draw some sketches of why I think Fig 8-17 is questionable. Earlier I wrote that profile of a surface must always have a basic dimension to describe the shape. (Of course profile's relationship to the datums doesn't have to be basic, but any dimension defining the shape itself should be basic, in my understanding of para. 8.2.)

See the attached figure. The first example applies profile to a flat surface. We have established that this is OK -- the basic dimension is zero (no curvature; a mathematician could even say a radius of infinity) so it is identical to a flatness callout.

I presume everyone is also OK with the second picture -- the surface is slightly curved, so a basic dimension is required to define the "true profile."

The third and fourth pictures are the same, but they have a more dramatic curve. Isn't it true that I must give the radius as a basic dim, not a ± ?

The last picture just takes it to the full curve, which we call a circle. I'm proposing that the diameter of the circle must be basic, just as the other radii were basic. But I am hearing from some folks that suddenly it's OK if this diameter is directly toleranced.

I don't mean to be stubborn (I know I've even insinuated that the standard goofed on this), but help me see what I'm missing that makes it OK to apply profile of a surface to a hole that has a ± tolerance on its diameter.

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

 

[DeanD3W]

John-Paul,
I agree completely that if a size or shape characteristic of a profile tolerance zone can be expressed by a basic dimension, then it must be... Leaving that basic dimension off would mean that the drawing is incomplete. There are some who have taught otherwise, but I contend that the standard does not back this up... The problem is partly due to those figures that combine profile and plus/minus. They are confusing for sure.

The reason I say that what profile controls cannot be affected by the presence or absence of a basic dimension is that there will then be cases for which there will be ambiguity... Those cases are when a basic distance of zero, or a basic angle of zero, or any increment of 90 degrees, is present, so the basic need not be shown... We cannot then know whether a basic is present or not. Also for an annotated 3D CAD body (per Y14.41) the model is queried to get basic dimensions, so how could the presence or absence of a basic affect what profile controls for those cases..?

The 2D size tolerance and position that pmarc shows is a different animal though, in my opinion (clarification is needed in future standards on this)... The 2D size and position tolerances (on a circular cross section and its center point) may be a refinement on the control provided by the profile tolerance, couldn't they?

Dean

http://www.d3w-engineering.com

 

[Madhu454]

Hi,
I dont have the copy of 2009 std, the Figure 8-17 is it Fig 6-23 of 1994 standard.

Madhusudhan Veerappa
Mechanical Engineer

 

[SeasonLee]

Madhu454

Yes, Fig.8-17 of 2009 is same as Fig.6-23 in 1994 standard.

SeasonLee

 

[Belanger]

Dean,
I agree about basic dimensions sometimes (often?) being implied, such as a zero basic dimension of coincident lines. Same thing for CAD data; the "dimensions" in the CAD model are basic. So whether the basic dims are displayed directly or implied, a profile tolerance must be applied to a feature whose form is defined by basic dimensions. I didn't mean to imply that a literal basic dimension has to be shown on the drawing. But to place a toleranced diameter on a cylinder which will get profile of a surface tolerance is contradictory.

When dealing with a cylinder or cone, the issue is that the dimension defining the form (which must be basic) is inherently tied to size. See the attachment provided in my previous post.

I disagree with your last paragraph. I certainly understand the desire to separate size and form, but I think that the way profile operates on a cylinder/cone, there's no way to do so. Again, see the attachment; I can't really do it justice here with text.

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

 

[Belanger]

Pmarc, In your post of 14 July at 2:45, you said that there is no similarity to your proposal and boundary concept given in Fig. 8-24. Why? (I would say that that is a more proper way to use profile and position together on the same feature.) Is it because those feature control frames are stacked together?

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

 

[pmarc]

J-P, I said this not because position and profile FCF's are not stacked together in my proposal. I think there is a difference in geometrical interpretation of both methods, which does not mean 'my method' is the correct one. Actually the more I think about it, the more shortcomings I see. Figs. 8-17 & 8-18 indeed seem not to be the best thing that happened to Y14.5-2009 standard. I just wanted to somehow utilize them by combining with other tolerancing techiniques (positional tolerance in this case).

By appling positional tolerance separately from the profile I was additionally aiming for giving an option of picking RFS, MMC or LMC concept depending on the feature's function. Fig. 8-24 does not give it. The 'boundary' concept works fine only when (M) or (L) modifier is placed in the tolerance portion of position FCF. RFS concept would rather require usage of typical profile of surface approach. In my proposal (assuming everything else worked fine) simple addition or removal of material modifier symbol would do the thing.

 

[DeanD3W]

John-Paul,
There is a way to apply a size tolerance to a feature which also has a profile tolerance applied... If the size tolerance is tighter than the size control provided by the profile,then it's a refinement of at least the size, and possibly also the form of the feature (depending upon how much tighter it is than the profile value). I'm not saying that this would be a likely or good practice, but nothing in the standard precludes it.

For a cone, a size tolerance, if applied, can only be applied to a 2D cross section of the feature... What the size tolerance then means could be an issue, since a cone is not a feature of size. Let's just say for now that a 2D size tolerance is OK here... As long as the size tolerance range is tighter than the profile tolerance value that may also be included, then the size tolerance would have an effect and it would undeniably be valid. Again, not necessarily a likely or good practice, but we must have a clear and sensible requirement from a standard to say it's not valid.

I am firmly in the camp that says that profile and +/- should not be combined, but if pmarc's figure had a size tolerance range tighter than 0.2/cos(cone's included half angle) (tighter than +/- 0.1004 since the angle is 5 degrees on pmarc's cone)(assuming that the 2D size tolerance zone is radial and not normal to the surface of the cone), then this is a combination of size and profile that I think is just two separate and independent tolerances... The profile does its job and the size tolerance independently plays its own role. One thing about pmarc's figure though... That Position tolerance should only apply to the center point of the single cross-section... If only a standard provided clarification of that point, we would be better off.

One more thing to mention is that a 2D size tolerance on a cone seems odd, but industry does it every day with modifiers like "+DFT" or "-DFT" or the alternative practice of "Draft reduces material" or "Draft adds material". This practice is an imprecise one, but for small angles (draft), and hopefully relatively large tolerances, everyone seems comfortable enough with it.

Dean

http://www.d3w-engineering.com

 

[Belanger]

Dean, I think I understand your comments, and because of Fig. 8-17, I suppose I am obligated to accept such a practice. But to make that really work, they need to clarify paragraph 8.2 to say that there are times when a profile tolerance doesn't have to be applied to a true profile (i.e., basic dims).

I would be more likely to agree with all this IF we were talking about profile of a line. (This would be kind of the opposite of your scenario -- where the size tolerance is 3D but the profile tolerance is 2D.)

Here are some questions that arise in my mind if we say that a basic diameter is not always required for profile:

[li]If profile of a surface is applied to a cylinder where the diameter has a ± tolerance, would profile of a surface be identical to cylindricity?[/li]

[li]If profile of a surface is applied to a partial cylinder (think of an arc that sweeps only 30 or 40º), then is the radius of that arc required to be basic?[/li]

[li]If the answer to the previous question is no, then couldn't each picture in Chap. 8 of the 2009 standard be modified to eliminate basic dims, if so desired?[/li]

[li]If the answer to that second question is yes, then how far must an arc sweep before we say that it is no longer required to be a basic dim?[/li]

Once again, I understand the desire to unlock profile from a basic size, but I can't help thinking that we'll get backed into a corner somewhere in all this.

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

 

[DeanD3W]

John-Paul,
I must be stating my opinions in the wrong way...

Profile on a cylinder absolutely requires a basic diameter. Profile on a cone requires complete definition by basic dimensions, but if no datum features are referenced that definition may be only the basic included angle of the cone (since the tolerance zone is free to translate in the axial direction it effectively become variable in size). If translation in the axial direction is constrained by a referenced datum feature then a basic dimension to the cone's apex may complete the definition, or as an alternative, a basic diameter combined with a basic dimension to define the axial location of that diameter may be used. Of course if the referenced datum features constrain all degrees of freedom then the cone's axis must be located by two more basic dimensions.

Even with a fully constrained, and fully "Basic dimension defined" profile tolerance zone, there is nothing that precludes the application of a sufficiently tight size tolerance to refine the size and possibly form of the feature. Not that I would recommend this, but nothing in the standard says this could not, or should not, be done.

Dean

http://www.d3w-engineering.com

 

[Belanger]

Dean, I think I see the reasoning if some careful caveats are in place: only on a cone, and only if no datum references are given. The bit about axial translation makes sense; since there may be some movement in that direction, the exact diameter cannot always be nailed down. (I hereby retract my questions re Fig 8-17!)

pmarc's picture has datum references on the cone, so for that example I think my comments have merit. The issue that remains open is how to determine bonus tolerance in the case where profile is used on these cones. (See PrDave00's post.)

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

 

[pmarc]

DEAN, JOHN-PAUL,

Thanks a lot for your really valuable comments about my proposal.

I have been thinking and thinking about figs. 8-17 & 8-18 in Y14.5 2009 edition and it is really interesting that these figures have not been changed comparing to 6-23 & 6-24 in Y14.5M-1994 - therefore I suspect there has to be a reason for keeping them in the standard and there has to be a logical explanation of how to understand them without assuming they are inappriopriate.

DEAN, if I got you correctly, you think that my concept could work if a size tolerance was a refinement of profile of a surface tolerance value divided by cosine of cone's half angle. But looking at 8-17 for instance it is rather not the case - size tolerance is much greater than profile tolerance value. And I believe it can be explained if size dimension and profile of a surface are treated as two completely independent requirements. With such approach I do not see any conflict between them. Profile controls form of a cone's surface of revolution only (without impacting its size) while the diameter dimension limits size of single circular element (base of the cone). IMO, these two requirements can be met independently. Please take a look to attached presentation (page 1) in which I tried to explain graphically my point of view using my proposal.

JOHN-PAUL, in your last post you said that 8-17 could work only if no datum reference in profile of surface FCF was given. I would say that addition of at least A datum to profile callout (like I did in my proposal) is not making the figure vague and is not conflicting with anything in the standard. Referencing A in the FCF orients profile tolerance zone relative to datum plane A. Please refer to page 2 of attached document to see how I understand presence or absence of datum reference A in profile FCF.

http://files.engineering.com/getfil...-40c7-b557-44b1f2a32109&file=profile_cone.pdf

 

[DeanD3W]

pmarc,
I'm not entirely in agreement that figure 8-17 provides a helpful example.

In the figure you attached I think all that you assert would be true if you used a customized datum reference frame and specified "A" as instead "A(v,w)"... This way A provides orientation constraint to the profile tolerance zone, but it does not constrain translation in the x direction as it normally would. Normally, the reference to A would constrain the cone's apex in the axial ("x") direction and therefore make the profile effectively control "size" of the cone (which can be viewed as "at each cross-section" if that's more comfortable, since a cone is not a feature of size).

Dean

http://www.d3w-engineering.com

 

[axym]

Hi All,

I've been busy this week so I haven't had time to follow or contribute to this thread until now. Very interesting discussion.

I would agree with J-P and Dean that allowing +/- to be mixed in with profile and alter its meaning is not one of Y14.5's brightest moments. One of the main objections I have to this mixing is that it is presented in a non-rigorous "definition by example" way. All we are given are figures 8-17 and 8-18, in which a +/- tolerance can somehow take away a profile tolerance's ability to control the "size" of a feature. A cone is an unfortunate feature to demonstrate this on, because translating a cone along its axis has a similar effect to changing its "size". IMHO, Figure 8-18 is a conceptual train wreck. We also have Figure 8-27, in which a +/- tolerance somehow un-refines (coarsens?) the location control usually provided by profile. Are there other cases in which we can replace a basic dimension with a +/- tolerance and change the meaning of profile? Like the cylindrical surface J-P mentioned, with both a profile tolerance and a +/- size? If we replace a basic angle with a toleranced angle, will this take away a profile tolerance's ability to control orientation? Where does it end?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca