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

 

[ptruitt]

Why not use a composite profile tolerance and all basic dimensions?

Peter Truitt
Minnesota

 

[Belanger]

Evan, I agree that profile with plus/minus can lead to a trouble, but only in the case of Fig. 8-17. That's because profile intrinsically controls form, and when dealing with a cylinder or cone, the very number that defines form (diameter) is also the one that controls size. With Dean's comments, I feel a tad better about it now, but I think we all agree that some clarification in the standard would be helpful on this specific point.

However, I wouldn't take issue with Fig. 8-27 because that plus/minus dimension has nothing to do with the form of the surface being toleranced. That is merely a location dimension, and the profile tolerances are not intrinsically required to control location: it's an optional add-on.

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

 

[DeanD3W]

John-Paul,
I think Figure 8-27 (Y14.5-2009) should be deleted from the standard... With "A" referenced, the profile tolerance zone would be constrained in location and a basic dimension of 80 mm must then be provided.

Figure 8-18 must have the reference to datum feature B deleted.

Dean

http://www.d3w-engineering.com

 

[Belanger]

Dean... here's the best way to think about profile: It always controls form (that is its intrinsic purpose). It can also control orientation (if a datum reference is given). And it can also control location (if a datum reference is given and a basic dimension back to the datum is given), and location obviously includes orientation as a sub-control.

Fig. 8-27 is the middle of the three scenarios I describe; datum A is meant for orientation purposes only.

Also look at paragraph 8.2, which says it this way: "Profile tolerances are used to define a tolerance zone to control form or combinations of size, form, orientation, and location of a feature..."

Fig. 8-27 controls a combination of form and orientation. In this case think of it as parallelism of "each element," where datum B helps define the orientation of the elements to be sampled. So a basic dimension is not required.

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

 

[DeanD3W]

John-Paul,
The way to think about profile cannot include misconceptions that are not explicitly supported by the standard. The figures that have been pointed out here cause confusion and what your saying here will do the same.

The presence or absence of a basic dimension cannot be used to determine what profile controls. This is a common misconception that others have written into their books and included in their training. It is a misconception that finds support only by the implication provided by a couple of figures in the standard that must be revised.

I think this is the highest priority issue to get clarified in the next version of the standard. Only after this will the improper training, and confusion it generates, stop.

The presence or absence of a basic dimension cannot have any effect regarding what profile controls since there are times when basic dimensions are not shown, such as distances of zero or angles that are zero or any increment of 90 degrees. We also don't show basics if annotating a 3D CAD model per Y14.41 instead of using a 2D drawing... Since one has no way of knowing whether a basic is present or not for those cases where they're just not shown for other reasons, then it is completely illogical to depend upon their presence or absence to determine what profile controls.

Only the capability of the referenced datum features to constrain the profile tolerance zone determine what is controlled. If there is a desire to release one or more of those degrees of freedom then now with Y14.5-2009, a customized datum reference frame can be used.

Sorry to be so blunt, but this issue is one that needs to get clarified and resolved asap. It's a big cause of confusion within a subject that has, as part of its purpose, the resolution of confusion.

Dean

http://www.d3w-engineering.com

 

[Belanger]

It's OK to be blunt, but I really think you're stirring up a non-issue. Why is it a misconception to state that profile tolerances can control orientation but not location? There's an example of such in Fig. 8-27. It's true that more pictures of this usage might be helpful, but I'm at a loss for how we can claim that such usage is not even allowed. See the attached graphic for a quick comparison that I've used in the past; you will agree with the second example but probably dislike the first example.

You say that "the presence or absence of a basic dimension cannot be used to determine what profile controls." I would say that it can. The only reason that I hear for why it can't is in regards to the case of dimensions not being displayed.

But there are already rules in place for that. See paragraphs 1.4(a) and 2.1.1.2 (and also Y14.41). If the distance back to a datum is not shown and it's understood to be basic, then that profile tolerance controls location. If the drawing leaves off dimensions as a general practice, but shows the distance back to the datum with a direct tolerance, then the designer is really trying to say something: that particular profile tolerance controls orientation only (and form, of course).



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

 

[DeanD3W]

John-Paul,
It is a misconception to say that the presence or absence of a basic dimension will affect what profile controls. My statement in the post above is very clear on this, so I am completely confused about how you could have misunderstood what I was describing as the misconception. Of course profile tolerances can be used to control orientation and not location... They do this when the datum features referenced constrain only the orientation of the tolerance zone or if a customized datum reference frame is used to release the translational degrees of freedom that would otherwise locate the tolerance zone.

The sections you cite say nothing to support the assertion that some people make that what a profile call-out controls is affected by the presence or absence of basic dimensions. Nothing in the standard says this. To take that position is illogical, when all things are considered. Yes, some confusing figures that need to be deleted or revised imply this, but no words at all explicitly say this.

If you think this is a non-issue, then you haven't seen the drawings that I have that were produced by a group that had received training that taught them the profile misconception which they then tried to run with. The drawings were nothing but utter confusion and the reason for this was directly due to this very real issue.

Dean

http://www.d3w-engineering.com

 

[Belanger]

Dean, I hope we're not boring the others. (Perhaps this topic of Fig. 8-27 deserves a separate thread?)

I encourage you to offer more explanation of the problem, because I indeed see no issue with relying on basic dimensions (or lack thereof) to dictate whether the profile tolerance controls orientation or location. If the drawings you mentioned really did run with this concept but to a wrong conclusion, I'd be interested in where they really made a wrong turn, because the concept of Fig. 8-27 is sound in itself.

You keep saying that it's a misconception to say that the presence or absence of a basic dimension will affect what profile controls. Yet you agree that profile can control orientation (not location) "when the datum features referenced constrain only the orientation of the tolerance zone..."

The natural question then becomes: How are we to know when the datum features referenced constrain only orientation? Can't that easily be determined (a la Fig. 8-27) by seeing that the distance to the datum is directly toleranced, not basic?



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