Smart questions
Smart answers
Smart people
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

randy64 (Aerospace) (OP)
13 Aug 09 9:59
I am seeing a conflict on how this works.

I am in a training class right now (TCI, Al Neumann). He states that Perpendicularity can be referenced to datums that are not perpendicular to the surface being held perpendicular. He has an example in his workbook showing it that way also. He refers to Perpendicularity, Parallelism and Angularity as Orientation controls (which they are), but seems to indicate that they are really flatness controls with orientation and that Perp, Par and Ang are just our perception of the direction of orientation.

In Alex Krulikowski's book "Fundamentals of GD&T" he explicitely states that the surface being called Perpendicular must be perpendicular to the datums it is being referenced to in the feature control frame.

Which is it? I've always gone with Krulikowski's interpretation. If we didn't, we could just get rid of Perp, Ang and Par and call it all Orientation.

What says you?

Thanks.
dingy2 (Mechanical)
13 Aug 09 10:14
Perpendicularity is an angularity control but this one is set at 90 degrees. It is not strictly angularity though.

Perpendicularity on a flat surface also includes flatness. In other words, if one had a .010 perpendicularity tolerance in the feature control frame, it means that when one measured the full surface set up on 90 degrees, we should not have a dial indicator movement of more than .010. It can be all angle (indicator increases/decreases as it is moved) or all flatness (indicator is 0 at the beginning and end of the angle but movement in the centre).

Perpendicularity on a axis, such as a cylindrical pin, will include its straightness. Again, it can be all angle or all straightness but most likely a combination of both.

Hope this helps.

Dave D.
www.qmsi.ca

randy64 (Aerospace) (OP)
13 Aug 09 10:24
So dingy, are you saying that you would agree more with Krulikowski's take on it?

To clarify, this is about 1994. I have found an example in 2009 that does it the same way Nuemann does it.
dingy2 (Mechanical)
13 Aug 09 11:17
randy64

Sorry but I need an example before I can determine whether or not the example meets the 94 standard. There are many areas in the 2009 standard that are not applicable in the 94 standard.

Dave D.
www.qmsi.ca

randy64 (Aerospace) (OP)
13 Aug 09 12:52
I'm not sure an example is needed. It's a pretty simple question: When calling a surface Perpendicular, do the datums called out in the reference frame have to be perpendicular to that surface? For further clarification, I am referring to the secondary datum. They both show the primary being perpendicular.

Neumann says no, Krulikowski says yes. Which is correct?

Thanks.
powerhound (Mechanical)
13 Aug 09 13:17
Krulikowski is correct. You can't call out perpendicularity to a datum that is not perpendicular to the feature being specified. In fact, this is so far off base that it makes me think that possibly you've misunderstood what was being said. You CAN call out perp to 2 different datums and both datums be perpendicular to the feature. Is this maybe what Neumann is saying? Neumann definitely knows his stuff.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

randy64 (Aerospace) (OP)
13 Aug 09 13:39
Nope, Neumann says just what I said. He even has an example of it in his work book. His take is that the datums are setting up a framework showing how the part will be held.

I'd like to scan and attach the pages from the workbook, but I'm afraid that would be against his copyright. I will, however quote from it a bit.

********************

Perendicularity ... to two or more datums, can be very confusing if you do not understand the datum reference frame concept.  It is important to remember that the datums only set up the part. The part, in this case, is set up with 3 points on A and 2 points on B. The orientation or perpendicularity tolerance zones are oriented to the datum reference frame and not the datum features. The surface must then fall within the tolerance zone.

The perpendicularity specification reads: This feature is perpendicular to the datum reference frame which is established, in order, by datum features A and B.

***********************

The above is accompanied by a picture showing a block with Perp called out to 2 datums. Datum A is perp, but datum B is actually a parallel surface.

And I'm not sure where he's getting the "perpendicularity specification" info. I can't find it in my copy of ASME Y14.5M-1994.

Powerhound, I agree with you, but this is Neumann's interpretation, and from what little bit I've seen, it's the interpretation that is used in the 2009 version.
caseynick (Mechanical)
13 Aug 09 15:14
When calling a surface Perpendicular, do the datums called out in the reference frame have to be perpendicular to that surface?

No. The surface in question has to be oriented according to the datum reference frame. In the example you are referring to that means the perpendicularity tolerance zone is  perpendicular to the primary datum and clocked by the secondary datum. The tolerance zone is, in fact, parallel to the secondary datum.
The datum features are used to set up the datum refernce frame.
The datum reference frame is used to establish the perpendicularity tolerance zone.
 
MechNorth (Mechanical)
13 Aug 09 15:37
I think there's a missed detail in here.  The datums must be mutually perpendicular.  The datum features do NOT have to be mutually perpendicular.  There is nothing in the standard that indicates that the datum plane and the surface generating it must be coplanar.  See if this tip helps:  http://www.tec-ease.com/tips/january-01.htm

The original post wasn't clear to me, and it isn't fair to comment on Al's material without knowing the exact wording rather than a paraphrasing.  Hope this helps.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

powerhound (Mechanical)
13 Aug 09 18:25
Just scan the illustration. I can't get past your assertion that a feature can be specified as perpendicular to a datum to which it is not perpendicular. If Al Neumann has somehow justified this, I have got to see it to believe it.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

randy64 (Aerospace) (OP)
13 Aug 09 19:23
caseynick has stated Neumann's case exactly.

MechNorth, I posted a direct quote from Neumann's workbook above. No paraphrasing.

powerhound, I can't get past it either, but it's there. Check out the attachment.

Overall, I understand what Neumann is saying, but it's very counter-intuitive. To say that a surface is perpendicular to datum B, when the drawing plainly shows that they are parallel makes my head want to explode.  But really, I think phrasing it that way ("a surface is perpendicular to datum B") is not what Neumann would say. I think he would say "Set the block to datum A, then datum B, and then check the surface to make sure it it in the tolerance zone," or maybe, "The surface is within the tolerance zone when held relative to datums A and B."

Even though I can wrap my brain around what Neumann is saying, I still think it is incorrect. I don't see anything in ASME Y14.5M-1994 that supports this idea. If you look at the definition of perpendicularity in 6.6.4, it states "Perpendicularity is the condition of a surface, center plane, or axis at a right angle to a datum plane or axis." It says AT A RIGHT ANGLE TO A DATUM PLANE (caps for emphasis, not yelling). To me that excludes datums that are not perpendicular.
powerhound (Mechanical)
13 Aug 09 20:49
Wow, you weren't kidding. This is contrary to anything I've learned about perpendicularity. A datum reference frame is made up of mutually perpendicular planes by default. There should be no need to specify datum B in the illustration. I'm gonna need some help from someone here that knows what's going on. How about you Jim? Can you help me understand this too? If datum B were the surface facing us, then it would be clear. If I were in a class that tried to pass this off as legit, I think I would seriously challenge the instructor...offline of course, not during the class.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

powerhound (Mechanical)
13 Aug 09 21:08
What I see on the illustration is a confusing way of specifying "profile of a surface". While the standard specifically says that the perpendicular condition is at a right angle to a datum. It doesn't say it CAN'T be used some other way...but that's pretty lame IMO.
The standard does show conditions where 2 datums are used but the illustrations are totally different than yours (see Fig. 6-35).
Man, I'm really itching for a good explanation of this one. Thanks Randy...this is a good one (at least I think it is).

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

randy64 (Aerospace) (OP)
13 Aug 09 21:52
powerhound, sounds like you're experiencing the same "exploding head syndrome" I'm experiencing! LOL!

The thing is, an almost identical picture is in ASME Y14.5M-2009. I think if ASME is going to do it this way, it shouldn't be called Perp or Par - it should all be Angularity and sometimes the angle happens to be 90 degrees or 180 degrees. Or they could come up with a new symbol and call it Orientation.
caseynick (Mechanical)
14 Aug 09 6:42
ASME Y14.5M 6.6.1
"Relation to more than one datum feature is specified  to stabilize the tolerance zone in more than one direction."
In the case of perpendicularity the secondary datum is solely to control a rotational degree of freedom. See fig.6-35. Datum B could just as easily be the short surface on the left side of the illustration and it would be a perfectly legal callout. The tolerance zone needs to be oriented to the primary datum and rotationally controlled by the secondary datum in either case.
dingy2 (Mechanical)
14 Aug 09 8:20
There is nothing wrong with the drawing. We have a plane that is perpendicular to datum A and also datum B using a 2 point set up.

If this plane was only perpendicular to datum A, it could still be skewed on the other axis while controlling the tilt. Having it also perpendicular to datum B orients the plane.

Dave D.
www.qmsi.ca

randy64 (Aerospace) (OP)
14 Aug 09 8:24
caseynick, Fig. 6-35 proves my point. It even states, "The surface must lie between two parallel planes 0.12 apart which are PERPENDICULAR TO DATUM PLANES A AND B."

You said "In the case of perpendicularity the secondary datum is solely to control a rotational degree of freedom." I don't see that anywhere in Y14.5M-1994. Everything I see says that the surface must be perp to the datums - not a word about "rotational degree of freedom." I suppose that could be derived from the use of the word "stabilize" in 6.6.1, but without explicit direction, I think we must go with what we are given, and that means in this context stabilization is attained through perpendicularity to two datums.
randy64 (Aerospace) (OP)
14 Aug 09 8:27
dingy2, are you looking the same picture I am? The one that I attached? Datum B is parallel to the surface in question, not perpendicular.
dingy2 (Mechanical)
14 Aug 09 13:12
randy64:

If you are talking about your posted picture, then yes I am. Datum B is perpendicular to datum A as I see it.

Dave D.
www.qmsi.ca

dingy2 (Mechanical)
14 Aug 09 13:23
randy64:

My previous statement is incorrect.

Datum B should not have been placed on the particular surface but on one of the ends. Datum B is indeed parallel to the feature but perpendicular to datum A. If datum B was on one end, then the surface would have been perpendicular to both datum A & B.

I now agree that the drawing is incorrect. I should look more closely at the drawings in the future.

I would suggest that you send a note to the author of this drawing.

Dave D.
www.qmsi.ca

randy64 (Aerospace) (OP)
14 Aug 09 13:30
dingy2, I wish it were just a picture that was in error. In fact, the picture represents an interpretation that states that the secondary datum does NOT have to be perpendicular to the surface in question - it is merely used to control rotation.

I believe this interpretation to be in error.
vigildesign (Mechanical)
14 Aug 09 13:34
Look at the angularity callout in fig. 4-24 in Y14.5-1994.  It is controlling perpendicular to datum "B".

 

Marcelino Vigil
GDTP T-0377
CSWP

randy64 (Aerospace) (OP)
14 Aug 09 13:44
vigildesign, you're right. Datum B is perpendicular to the surface in question (datum D). It is shown on the drawing to be 90 degrees from the datum B. I have no problem with a datum perpendicular to a surface controlling the perpendicularity of that surface. I do have a problem with trying to control the perpendicularity of a surface with a datum that is parallel to that surface. Just doesn't make sense to me.
PaulJackson (Automotive)
15 Aug 09 7:58
I don't see anything wrong or odd about Al's example and agree totally with caseynick! The caption in figure 6-35 pertains to that example since the tolerance zone happens to be oriented perpendicular to both datum features. The extension of orientation control to more than one datum feature in 6.6.1 makes no requirement for the zone to be perpendicular to all datum features in the DRF.

Paul
randy64 (Aerospace) (OP)
15 Aug 09 8:44
PaulJackson, doesn't the definition of Perpendicularity make a requirement for the zone to be perpendicular to all datum features in the DRF? It [6.6.4] states, "Perpendicularity is the condition of a surface, center plane, or axis at a right angle to a datum plane or axis." To me it couldn't be any plainer than that. Yet you are right, 6.6.1 makes no requirement of perpendicularity, but that's because it is a general statement on orientation. It is simply stating that two datums can be in relation to the surface in question, that's all. It is further defined for Perpendicularity in 6.6.4.

If Neumann's way of thinking on this subject were accepted, it would hold true for Parallelism also, i.e. you could reference a secondary datum surface that was actually perpendicular to the surface that is being held parallel. But that condition is never shown in Y14.5M-1994. Nowhere can I find a surface being held parallel to two datums. This is because it can't be done, it's the nature of Parallelism. I believe the same to be true of Perpendicularity - it CAN be perpendicular to two surfaces at once, so it can be held to two datums.

I think those that are agreeing with Neumann are creating something that is not in Y14.5M-1994. I think it goes over the line of creating something that is not really there.It is at the least a very liberal interpretation of Y14.5M-1994. When it comes to documents like this, I tend to be very conservative - I look at what is there and go within that framework, adding as little as possible.

All the responses in agreement with Neumann so far have not pointed to anything in Y14.5M-1994 that allows this, yet I've pointed out things that do not allow it and no one has directly refuted it.

Now, I try to be as open minded as possible. That's the reason I started this thread. I saw something that was different than what I had always believed and figured I had better hear both sides so I could make an informed decision. The knowledgeable people on this forum have changed my way of thinking on other subjects in the past, so I'm open to that, but so far I stand unconvinced on this one.
dingy2 (Mechanical)
15 Aug 09 10:37
Paul:

I respectfully disagree with you but, initially, I didn't think anything was wrong with the example.

The surface on example 6-35 of the 94 standard reflects a plane that is perpendicular to both datum A and also datum B.
The example in discussion is not the same. The feature is perpendicular to datum A but parallel to datum B.

Maybe there is an figure in either the 94 or 09 standard that reflects the example but I don't think so. If there is, please let me know.

Dave D.
www.qmsi.ca

randy64 (Aerospace) (OP)
15 Aug 09 10:47
dingy2, the 2009 standard does indeed have a picture very similar to the one I posted (one of the datums parallel to the surface in question), but all the verbage about orientation is the same as the 1994 as far as I can tell.

My customer follows 1994 right now, so that's my main concern. If ASME has adopted Neumann's take on it for 2009  then, as I stated before, it shouldn't be called Perpendicularity IMO. It should all just be called Orientation or Angularity.
dingy2 (Mechanical)
15 Aug 09 11:31
Figure 6-4 in 2009 edition is exactly a replica of your example so the example is correct to the 2009 standard.

The angularity symbol as shown in figure 6-4 as an alternative practice is much more precisely reflects the situation and should be used rather than perpendicularity.

Dave D.
www.qmsi.ca

axym (Industrial)
15 Aug 09 13:33
ASME Y14.5M-1994 states (in 6.6.1) that more than one datum feature can be specified in an orientation control.  But then it only addresses "pure" cases in which the considered feature has the same relationship to both datum features.  I don't think that the explanations and examples in Y14.5-1994 give a definite indication of what symbol to use in "mixed" cases like the one in the TCI example that was posted.  It's open to interpretation, so I don't think we can really determine what is "correct" per the standard.

Let's revisit Fig. 4-24 on page 69, in which there is an Angularity control that references two datum features.  The considered feature (a planar surface) is at an angle of about 30 degrees from datum plane A (the basic angle is not shown) and 90 degrees from datum plane B.  Technically, this meets both the definition of Angularity in 6.6.2 and the definition of Perpendicularity in 6.6.4.  The surface is at an angle other than 90 to a datum plane, and it's at a right angle to a datum plane.  I think we all agree that the Angularity symbol is appropriate here and not Perpendicularity, but we disagree on the reason why.

What it comes down to is this question.  If we wanted an orientation control for the same feature, that references B as primary and A as secondary, what symbol should be used?

One option is to choose Angularity (really, to rule out Perpendicularity) because the considered feature is not at a right angle to both datum planes.  Another option is to choose Perpendicularity because the primary relationship is perpendicular (i.e. the considered feature is at a right angle to the primary datum plane).

Both options will be confusing to some.  If Angularity is used, some people will be poring over the drawing trying to find the non-90 basic angle between the considered feature and datum plane B.  There is also the possibility of a Perpendicularity control changing to Angularity if a secondary datum reference is added.  If Perpendicularity is used, some people will find this non-intuitive because the considered feature is not perpendicular to datum plane A.

Personally, I'm most comfortable with the option of basing the symbol on the considered feature's relationship to the primary datum feature.  This is the approach suggested in the TCI book, and used the most in industry AFAIK.  This isn't perfect, but it doesn't make my head explode.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

PaulJackson (Automotive)
15 Aug 09 13:44

Quote:

"PaulJackson, doesn't the definition of Perpendicularity make a requirement for the zone to be perpendicular to all datum features in the DRF?

No I don't think so.

Quote:

"It [6.6.4] states, "Perpendicularity is the condition of a surface, center plane, or axis at a right angle to a datum plane or axis."

I have always interpreted this statement as "establishing a right angle (90 degree implied) basic relationship between the primary datum feature ("a" datum plane, or axis) and the featured controlled for orientation." No more, no less... likewise a zero or 180 degree implied for parallelism and a specified basic to the primary for all else.

Paragraph 1.1.4 covers the illustration vs. definition justification.

I would be just as happy with one symbol for orientation, having implied basics specified, and as many datum feature designations as necessary to constrain the rotational degrees of freedom that are functionally necessary for the control.

paul
    
 
powerhound (Mechanical)
15 Aug 09 14:18
Paul,
  As I mentioned in an earlier post. This seems to be another way of specifying profile of a surface, only more confusing. If the symbol were changed to profile of a surface, then it would mean exactly what you and Evan are saying except no one would be questioning it or disagreeing over it. I don't see any reason to use this method in lieu of profile of a surface. This one causes problems and the profile of a surface doesn't.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

PaulJackson (Automotive)
15 Aug 09 15:22
Powerhound Profile constrains translations as well as rotations. Orientation controls constrain only rotations.

Paul
powerhound (Mechanical)
15 Aug 09 15:32
So are you saying that profile of a surface will mean something different than this iteration of perpendicularity?

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

randy64 (Aerospace) (OP)
15 Aug 09 16:29
PaulJackson, I think you're reading more into it than is there with your interpretation when you say "and the feature controlled for orientation." 6.6.4 doesn't say that, it says "Perpendicularity is the condition of a surface, center plane, or axis at a right angle to a datum plane or axis." In my mind, saying "a" datum plane doesn't limit you to one datum plane. I interpret that as "any" datum plane.

Like I said above, I'm conservative in these matters. I believe my interpretation fits within what is stated within the standard, but Neumann's does not.

I don't have access to a lot of GD&T material, but I'd be curious if anybody can share other sources that interpret this the same way Nuemann does. As I stated in my original post, Alex Krulikowski states in his book that Neumann's interpretation is wrong. He has a flow chart and one of the questions is "Is the toleranced feature shown 90 degrees to the datums referenced?" If the answer is "No", then he calls it an "illegal" callout. I'll attempt to link it for you. Scroll to page 185.
PaulJackson (Automotive)
15 Aug 09 16:32
It would if the Al Newman example was changed to profile but not the figure 6-35 example.

Paul
PaulJackson (Automotive)
15 Aug 09 16:53
Randy,

Alex and Al are both on the committee that codifies the standard but neither of their own materials are the standard! It appears that one could say by Alex's flow chart of leagal/illegal and Newman's illustration that the two of them differ in their interpretation... I'll go with Al's from what I read in the standard... You can go with Alex from what you read in the standard... it appears that the we are not alone in our differing opinions.

Paul   
randy64 (Aerospace) (OP)
15 Aug 09 17:14
Paul, you're no fun! I think we must stay on this forum and argue until one of us wins!! winky smile

Yeah, I don't think planes will fall out of the sky or cars will fall apart over the interpretation of this. I guess I'm just a little OCD about having consistency in the standards I'm following.

Peace.  
pmarc (Mechanical)
15 Aug 09 18:04
Randy,

As you said in one of your first posts, in Y14.5M-2009 exactly the same situation like you have is shown (fig. 6-4). I totally agree with you that it looks illogical (or at least confusing) to control perpendicularity of a feature relative to datum feature that is parallel to it, but on the other hand the standard clearly shows that this is legal, so there should be no doubt about it. In fig. 6-4 the secondary datum is invoked only to constrain an additional rotational degrees of freedom of the DRF. This leads me to conclusion that only primary datum feature from Perpendicularity callout should be perpendicular to specified feature and it is less important whether the secondary datum feauture is parallel or at right angle to controlled surface - it will always better orientate tolerance zone. I also agree that this situation can be considered as a contradiction to general definition of perpendicularity from para. 6.3.3.

Regarding the discussion who is right, Alex or Al:
Looking at fig. 6-4 from 2009 standard, I think you must admit that Alex's flow chart in step 2 can not be considered as a correct one. However Alex's book is basing on 1994 standard where such situation wasn't described so the field for interpretation has been left. If new edition of his book comes up I am pretty sure step 2 will be re-stated.

Regards
  
powerhound (Mechanical)
15 Aug 09 18:43
Paul,
  That's my point exactly. Fig. 6-35 has nothing to do with what I'm trying to say. I have no problem with 6-35. I do have a problem with Al Neumann's interpretation though. What I'm saying is that if you were to exchange the perp with profile of a surface -in Neumann's example- it will still mean exactly what you are saying it means as it is now, but it won't be open to any interpretations. Your interpretation that states "...and the feature controlled for orientation." is not an interpretation, but an addition to what the standard says because the standard says nothing about orienting a plane for perp. The orientation of the plane in the example is controlled by the limits of size, in this case the 11.9 dimension. If you want the plane oriented more closely than that, then you use Profile of a surface and call it out to A and B.
  I guess one could look at it like this; which method would be more clearly supported by the 1994 standard in the case of a lawsuit? I see no support whatsoever for this method that Al is teaching. The support for profile of a surface in this case, is overwhelming.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

PaulJackson (Automotive)
15 Aug 09 20:44
No Powerhound if Newman's example was changed from orientation to profile the controlled surface opposite [B] would necessarily have a basic displacement from [B] that the profile would tolerance in addition to the orientation to [A|B]. With this change to profile size between B and the controlled surface would be dependent upon both [B]'s Orientation tolerance to [A] via either Perpendicularity or Profile control as well as the controlled surface's Profile to [A|B].

The use of the Perpendicularity control negates any translational relationship in Newman's example so only orientation is controlled from [A|B]. Size has nothing to do with this check it could be twice size and still be oriented perfectly to [A|B].

Paul
powerhound (Mechanical)
15 Aug 09 22:30
I'm not sure if I understood what you said in your first paragraph but profile isn't limited to basic dimensions only, as shown in Fig. 6-18. You can use +/- tolerancing in conjunction with a profile of a surface callout. Regarding the issue of combined tolerances, that's up to the engineer to figure out.

Size has everything to do with it's orientation. The distance of the surface from B cannot exceed it's size tolerance at any point so this provides a measure of orientation control to B. If you want to orient it more tightly to B only but not necessarily A, then you would use parallelism, if you want it oriented more tightly to A but not necessarily to B, then you use perpendicularity. If you need them both oriented more tightly, you use profile of a surface. None of these require basic dimensions and they are all fully supported in the 1994 standard.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

MechNorth (Mechanical)
16 Aug 09 0:08
Sorry guys, been off visiting & such for a day or two.  OK, I have SEEN an example like Al Neuman has in his material, as referenced above.  It IS counter-intuitive, but not specifically indicated as illegal in the '94 standard.  And I was given the same explanation, i.e. that it is viewed as an Orientation control rather than just a Perpendicularity control.  I can accept it, because perpendicularity is just a special case of orientation, but I would never suggest it to anyone as the way to do it, nor endorse it as a practice to be taught when there are far clearer ways to achieve the goal.

There is a similar but different issue when you have a composite profile control with 3 or more levels.  Typically the first level controls the location, and any subsequent levels with datums referenced will refine the orientation.  It takes a bit to wrap one's head around the idea that on each refinement level you are primarily focusing on the last datum in the DRF, while also including the preceding datums .. it can be a mind bender, but usually is the best way (in the applications that I've seen) of achieving the goals.  When the surface is already located using a +/- tolerance, then the profile control (single segment or composite) will be refining orientation and form.

Personally, I would prefer that both parallelism and perpendicularity be eliminated and just Angularity in ALL orientation situations.  It's not a huge cognitive leap to see that two lines look 90-deg or 180-deg apart, so there really isn't a need for the other two controls.  

Keep in mind that just because something ISN'T specifically illustrated or included in the text of the standard, that does not mean that it's illegal.  An application needs to violate aspects of the standard to be an illegal application.

The example cited in Fig. 6-35 is clearly a valid application of two datums referenced in a perpendicularity control, and it makes sense because the surface IS perpendicular to both datums, as designed.  Good reference.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

powerhound (Mechanical)
16 Aug 09 1:35
I guess my issue lies in the fact that the standard says that perpendicularity is specified perpendicular to a datum. In every subparagraph of 6.6.4.1 the tolerance zone is specified perpendicular to a datum. Nowhere does it state that it can be specified parallel to anything, whether for orientation or not. Does that really mean we can add that to it and it should be okay? There is no symbol for perpenposiparalangulicity but I'm making one up, putting it on a print, and supporting it with the 94 standard cause nothing in it says I can't...laughtears

Seriously though...this has been an excellent thread. I'm glad these only come around every now and then, otherwise I'd never get any work done or sleep.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

ProfDon (Mechanical)
16 Aug 09 10:51
Hi All,
This was an interesting thread.  Having attended the Y14.5 meetings where this was discussed I found it interesting that you all had the identical discussion.  The line about "Relation to more than one datum feature is specified to stabilize the tolerance zone in more than one direction." was added to clear this issue up in the 1994 standard.  I know, you have to go by what is in the Standard since we can't all be at the meetings.  Well, look at where this statement is added.  It applies to all orientation tolerances--including perpendicularity.  Even with the addition of this statement, some folks remained troubled as is evidenced by this thread.  So, the Alternative Practice of using angularity for all orientation controls was added in 2009. Yes, a composite profile tolerance could have been used as another way to control the surface.  But, using an orientation control guides the reader where profile of a surface is not well understood.
Bottom line, Al is correct since adding additional datum references to any orientation tolerance, including perpendicularity, stabilize the tolerance zone relative to the datum reference frame.  MechNorth explained this very well.
 
axym (Industrial)
16 Aug 09 11:20
I'll start with my standard opening statement of "I agree with Paul Jackson on this one".  Profile would control the location and orientation of the considered feature in the Al Neumann example.  Pretty much the only case in which Profile would provide the same control as an orientation tolerance would be the "everything orthogonal" geometry of Fig 6-35.

Like Jim, I could live without specific controls for Perpendicularity and Parallelism.  I would like to see an orientation control that can be applied to any feature type and related to any datum reference frame.  This can be done with the lower tiers of composite FCF's but those are so confusing.

BTW, I like powerhound's comment about "perpenposiparalangulicity".  Didn't Julie Andrews and Dick Van Dyke sing that?

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

caseynick (Mechanical)
17 Aug 09 7:08
IMO
The example of perpendicularity in the 94 standard which shows the surface pepprpendicular to both surfaces is an example of one possible way to use the callout. The example of perpendicularity in the 09 standard, which pretty much matches the sketch that initiated this thread, is an example of another possible way to use the callout. It would be impossible for a standard to have examples of every possible way to use a particular gd+t control.

The appendix in 09 says that there has been no significant change from 94 in the perpendicularity callout.

The reason there is no secondary datum for parallelism callouts is that clocking/rotational control is irrelevant.  
p.s. Prof Don What about me? I ought to get an attaboy for saying the same thing way up the thread don't you think? smile
 
ProfDon (Mechanical)
17 Aug 09 8:10
Attaboy, caseynick.  
One comment, though.  If a hole is parallel to the primary datum feature and perpendicular to the secondary feature, I could see a secondary datum feature referenced in a parallelism callout in order to "stabilize" a cylindrical tolerance zone.  But, like caseynick said,"It would be impossible for a standard to have examples of every possible way to use a particular gd+t control."  The question I often ask is: "Does this geometric callout have one clear meaning to those who are knowledgeable of the standard?"  If the answer is "yes", it is a legitimate (legal) callout even though you cannot point to one exactly like it in the Standard.  It is called an extension of principle.  
 
caseynick (Mechanical)
17 Aug 09 8:25
Thanks.smile
And in regards to your comment: Of course. I should have said "....MANY parallelism callouts......"

 
dingy2 (Mechanical)
17 Aug 09 8:37
It is hard to believe that someone is teaching the application of perpendicularity when the feature is not perpendicular. That, in itself, is mind boggling but it does comply with the 2009 standard. No wonder people are so confused over GD&T.

I certainly can see someone training relatively knowledgeable GD&T personnel the use of angularity in this situation but perpendicular?? mmmmmmmm.



 

Dave D.
www.qmsi.ca

powerhound (Mechanical)
17 Aug 09 13:43
Being that some seriously credentialed people are saying that the example in Al's book, which is per the 94 standard, is legit, then I'll concede that it is valid, BUT I will still never specify perpendicularity using this method on any prints that I make. It's just not easily supported, IMHO, and there are other, more clearly interpreted and supported mehtods that produce the same results.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

ProfDon (Mechanical)
17 Aug 09 14:13
Hey powerhound,
I am with you.  The most important thing is to clearly communicate to the reader (customer).  There are a lot of tricky things you can say on a drawing that would baffle the best of them.  This was an interesting thread.  Attaboys to all who participated.
randy64 (Aerospace) (OP)
18 Aug 09 13:34
ProfDon, you said, "Bottom line, Al is correct since adding additional datum references to any orientation tolerance, including perpendicularity, stabilize the tolerance zone relative to the datum reference frame."

So, is Alex Krulikowski wrong when he calls such callouts "illegal"? (Reference my link above)

I sure wish someone would have spoken up in those 1994 meetings and forced some less ambiguous language. Adding the "stabilize" line seems like a weak attempt to me. In a standard of this sort it should be more explicit, IMO. I think the standard should stand on it's own, without knowledge of the backroom dealings that birthed it. If it isn't in the standard (and I still don't see Neumann's interpretation in there - in fact I think it is excluded) then it's not part of the standard. Discussions mean nothing, only what makes it into print matters.

I'm with powerhound - I don't see myself ever using Perpendicularity that way.
ProfDon (Mechanical)
18 Aug 09 20:02
I think Alex will admit that he might have slipped in this case.
I agree and acknowledge that it has to be in print.  I pointed out that the Standard explains the purpose of additional datum references where it is discussing all 3 orientation tolerances.  That is pretty clear to me.  But, standards like any language evolve and if this becomes an issue or winds up in court, it will be pointed out to the committee and clarified further.  That is how we got the new spotface symbol this time around.   
KENAT (Mechanical)
18 Aug 09 20:11
What kind of training is this by the way.  Is it "all you need to know to be on the 14.5 committee" or perhaps "advanced GD&T so you can confuse even knowledgable collegues".

If it's a really advanced course then fair enough but if it's a more basic level case, isn't this kind of thing a bit OTT?

KENAT,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

MechNorth (Mechanical)
18 Aug 09 21:14
Interesting question, Kenat.  Training material evolves over time, reflecting changes to the standards, and wider application and acceptance of the technologies involved.  Sometimes we add something in because we see an increasing demand for that particular nugget of knowledge, and later may find that it's over the heads of many who aren't at an advanced level ... so we sometimes take things out too.  When books are published for wide distribution, there is usually significant pressure to include more rather than less, and hopefully something "unique" for want of a better term.  My thoughts are that this topic should be focused into Intro, Intermediat and Advanced materials, but I know from first-hand experience that such an approach is not appreciated by most, and they often evaluate themselves as being significantly more capable than is the case.  In learning the Y14.5 standard, we re-read the standard numerous times by the linked-topic study method and keep re-reading it as we broaden our own exposure to new applications.  Sometimes it takes a sudden lightning-bolt moment to bring a bothersome concept into focus.   

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

KENAT (Mechanical)
18 Aug 09 22:22
Funny MechNorth.  I think we're maybe of a similar opinion.  They had a week long training session here just before I started that, having read the material, was probably at the Intermediate level.

Based on how people have (not) implemented it etc. I think a far more basic, and probably a bit shorter, "Intro" course would have been better.

Obviously, others may have a different point of view, but for me an Intro level course would probably focus on what to me is the bread and butter of GD&T - basic hole patterns ensuring fit/function.

When I had a chance to train some new interns that's what I did.  I only had an hour, no where near enough time to do it justice, but I attempted to give them an appreciation of fundamentally what tolerance was and then how to apply it to hole patterns.

I realize hole patterns aren't the be all and end all, and of course can get complicated in them selves, but the most common applications & errors I see are basic hole patterns so to me that's where the bang for the buck is.

KENAT,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

MechNorth (Mechanical)
19 Aug 09 11:39
Yup, Kenat, and I find that the focused needs at each company (and even within different sections of the same company) vary wildly.  Considering that, and without the "luxury" of being onsite long-term, often trainers and their materials have to cover the whole scope of the standard, though obviously some sections in greater & lesser detail.  What makes it worse is that so many of the topics are intertwined that we have to cover some topics that the trainees don't think are applicable ... inevitable scope creep.  Some instructors stick very tightly to their materials and timelines, while some of us divert to tangents to address the funkier applications of the class.  That's what keeps the training interesting for both sides.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

axym (Industrial)
19 Aug 09 13:14
GD&T can be a difficult thing.  It's one thing to learn the basic ideas, and something else entirely to learn them well enough to get all of the details exactly right.  And we all know the consequences of not getting all of the details exactly right.  The devil is in the details, as they say.

I often get requests to not cover the whole standard, and to just show the students enough to do their job.  But it's amazing how complicated things get even for garden-variety parts.  To inspect a typical position tolerance properly you have to understand the details of axes, actual mating envelopes, cylindrical tolerance zones, patterns, simultaneity, material condition, bonus tolerance, basic dimensions, datum features, datum feature simulators, datums, datum reference frames, degree of freedom constraint, precedence and non-override, datum shift, and virtual condition.  If any of these details are not treated correctly, the results can be wrong.

I've found that training that tries to keep things simple and glosses over details tends to be well received but causes confusion when applied later.  Training that deals with all of the details and complexities tends to cause confusion right away!  It's hard to find a balance that gives the students some job-ready GD&T skills without confusing the heck out of them.  All compressed into a couple of days, of course!

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

KENAT (Mechanical)
19 Aug 09 14:13
(To the OP sorry if this is too far off topic, I'll start a new thread if need be)

I suppose implicitly, I was invisioning a situation where there are more experienced folk that can be used as resources when people start getting into more complex areas and that will be reviewing the work for accuracy.  Obviously this isn't always the case.

I was thinking of a course that gets people up to the basic level, allows them to operate at that level for a while to get some real world experience, with support/review of their work while they learn.  I was thinking that eventually they would probably take a slightly more advanced training and/or (I know this is crazy talk, but bear with me) spend some time getting to know the standard, teaching themself, asking questions when they find something they don't understand...

However, I realize now I was clearly in some kind of fantasy.  I'm probably still at the stage that I don't really know enough to know what I don't know, but 90+% of the time seem to muddle through OK referring to the standard and thinking about things.  The other 10% I either ask here, find a work around or give upwinky smile.

KENAT,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

MechNorth (Mechanical)
19 Aug 09 14:34
Now THAT's funny, Kenat!  Progressive learning and internal resource mentoring !!! What do you think industry is, something intelligent & efficient?  Oh, my side hurts now from such a good joke!

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

KENAT (Mechanical)
19 Aug 09 14:41
Sorry, not sure what came over me, I'll shut up again.

KENAT,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close