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Question, What is the difference between A & B?

Question, What is the difference between A & B?

Question, What is the difference between A & B?

(OP)
I am a bit stumped.  Can someone please explain the difference between callout A and callout B?

RE: Question, What is the difference between A & B?

(A) Controls the axes of 4X 5.0 diameter holes within 4 parallelpiped tolerance zones (0.2 X 0.2, 10.0 deep) perpendicular to surface [A] and in a 32 X 32 square pattern.

(B) Controls the axes of 4X 5.0 diameter holes within 4 parallelpiped tolerance zones (0.2 X 0.2, 10.0 deep) perpendicular to surface [A] and in a 32 X 32 square pattern... that is displaced 9.0 from [B] and 9.0 from [C].

paul  

RE: Question, What is the difference between A & B?

WOW, that is a big part! 50" x 50" x 10" thk.
If that part is metric, read Y14.5, any edition.
Metric dimensions do NOT use trailing zero's!

The difference is that (B) has defined which edges to fixture the part from for inspection by defining the coordinate reference planes in all 3 directions.
In theroy they both are the same. The use of datum B and C is implied.

I haven't verified this, doing it from memeory, which means I could be totally wrong.
 

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

RE: Question, What is the difference between A & B?

(OP)
Regarding trailing zero's, our company uses them to help indicate default tolerances.

X.X = +/- 0.30
X.XX = +/- 0.15
X.XXX = +/- 0.08

I will take you for your word on the Y14.5, I had a hard time going through it - extremely dry.  Our titleblock and standard was from before my time, and I prefer it's use of the trailing zero.

RE: Question, What is the difference between A & B?

(OP)
ops, I forgot.

Thank you for all your help!

RE: Question, What is the difference between A & B?

Learn to love 14.5.  

Any other text books etc, even by committee members, still isn't "the standard".  In some cases they may put their own flavour or preference etc. into it which isn't explicitly in the standard.

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"?

RE: Question, What is the difference between A & B?

I have worked a number of places that used trailing zeros with metric dimensions to control tolerances. I would consider the title block tolerance or a similar note to take precidence over the no trailing zeros standard for metric dimensions. A defacto company standard.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net

RE: Question, What is the difference between A & B?

Isn't this exactly what composite position tolerance is for?

RE: Question, What is the difference between A & B?

The positional tolerance zone for a hole should be a cylindrical zone with diameter 0.2 X 10 long, so the position callout should have a diameter symbol before the tolerance.

It should be POS|Ø0.2|A instead of POS|0.2|A.

SeasonLee
 

RE: Question, What is the difference between A & B?

The postion tolerance for a hole doesn't have to be a circular zone.  If appropriate to function a rectangular tol zone is perfectly legitimate.  There is no "should" about it, at most a "is normally".

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"?

RE: Question, What is the difference between A & B?

The difference is that with (A) is that your hole pattern has no form control.  With (B) it does.  (A) is guaranteed to give you a hole pattern with targets that are out-of-square.

Here's why.  The outer 50 x 50 square has no angular tolerance between the sides.  Absent a note on the drawing, it's undefined.  With (A), your target is 9 units and 41 units from a plane which contacts the high spots on datum feature B, and 9 and 41 units from a plane whith contacts the high spots on datum feature C.  To the extent that those features may be mis-oriented with respect to each other (or to datum A), that's the misorientation you'll get in your hole pattern.

With (B) your targets vertically is 9 and 41 units from a plane which contacts the high spots on datum feature B and is perfectly oriented with respect to datum feature A.  your targets horizontally are also 9 and 41 units from a plane which contacts the high spots (or spot) on datum feature C and is perfectly oriented with respect to datum feature A and datum feature B.

If your trying to match a mating part, you probably want (B) and not (A).

RE: Question, What is the difference between A & B?

Also, as mentioned in an earlier post, the shape of your tolerance zone needs to be cylindrical -- put a diameter symbol before the 0.2 mm tolerance.

RE: Question, What is the difference between A & B?

Kenat

If a rectangular tol zone is the designer's intent, then the print should specify the tol on both horizontal and vertical direction, otherwise the diameter symbol should be added.

SeasonLee
 

RE: Question, What is the difference between A & B?

Fair point, they're either missing an fcf or a dia sign.

I think somewhere I saw about it meaning a square zone withouth the dia symbol but what you say sounds familiar for 14.5, or is it only required if you want a 'rectangle' rather than square.  I can't recall and this is a bit off topic.

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"?

RE: Question, What is the difference between A & B?

Quote:

The difference is that with (A) is that your hole pattern has no form control.  With (B) it does.  (A) is guaranteed to give you a hole pattern with targets that are out-of-square.

That is not exactly right MartinSR00.

If the basics were changed to limit dimensions then your point has some merit.

By declaring the four holes a pattern with the "4X" designation... linked to a feature control frame... all four features have a basic pattern relationship to one another regardless of datum feature designations. When [A] is added to the FCF those tolerance zones are oriented to [A]... and when [A|B|C] is added those zones are oriented and located relative to the DRF established by [A|B|C].

Paul
 

RE: Question, What is the difference between A & B?

Actually, Rule #1 gives form control based on the tolerance of size for either callout (based on the generic tolerances in the title block).  The position control doesn't control form.

As indicated above, for it to be a linear tolerance, the dimension arrow across the feature (i.e. not radially) needs to show the direction.  There is no expectation of a square zone just because the diameter symbol is missing.  The absence of the direction indicator makes callout (A)illegal.

Otherwise, the two callouts (A) and (B) are in conflict, as (A) is not a refinement of (B); they both have the same tolerance of 0.2 on position (ignoring the preceding point about absence of diameter symbol), and both refer to the same four features.  Thus, they are in conflict.  

Now, if this was a graphic generated just to ask what the difference is between the two callouts (assuming the cylindrical tolerance zone in (A)), then ...
Callout (B) establishes the location in space (as related to the datums) at which each feature should theoretically be; this includes orientation to each of the datums, including Datum A.
Callout (A) establishes only the perpendicularity requirements of the axis wrt Datum A.  As a result, the pattern of 4 holes (as established by the 4X) is free to float around as a group, maintaining general orientation and location wrt each other, but not to datums B or C.

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

RE: Question, What is the difference between A & B?

(OP)
MechNorth,

You are correct, the image was a graphic that represents my "question".  I did also forget the diameter symbol - was in a rush to get an answer quickly and omitted it accidentally.

I think it is clear;
A > gives an un-clocked/positioned pattern, but does keep the holes perpendicular to datum A
B > clocks and positions the pattern, while also keeping the pattern perpendicular to datum A

RE: Question, What is the difference between A & B?

Ryandias,

Yes, but not complete.  "A" not only doesn't lock down rotation, but also doesn't provide a location in space either, as "B" and "C" aren't referenced in the FCF.  

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

RE: Question, What is the difference between A & B?

At one company, we stated on the drawing that it complied with ANSI Y-14.5m-1982, then updated to ASME Y14.5m-1994. We also used trailing zeros. When I started there, I pointed this out since you can't have both. Either the drawing complies or it doesn't! Most CAd systems have to forced to put trailing zeros when doing netric standard drawings.
The obvious reason to conform to the standard is when handed a drawing, you don't have to search to see what the units are. If you see trailing zeros, then it is in inches. If you see leading zeros or no trailing zeros then it is a metric part.
 

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

RE: Question, What is the difference between A & B?

There are (or at least have been) problems with a number of CAD packages in that you were not able to set the trailing zeros option.  In other cases, once the company standard was defined, you couldn't override it on an individual drawing, so if you set for inches, your metric drawing would still have trailing zeros.  Then there's my favorite; typically if you use dual dimensions, then both the metric and inch dimensions both either have, or have not trailing zeros.  The net effect is that regardless of whether or not there are trailing zeros (or preceding zeros incorrectly applied to metric decimal fractions), it is still critical that the user of the drawing check the units specified on the drawing, otherwise you could be off by a factor of 25.4.

Now, as Matt says, as long as a company states the exceptions to the ASME Y1.5 rules (i.e. documents it and circulates that document), then it is accepted.   

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

RE: Question, What is the difference between A & B?

Matt,

If you state on your drawing that it complies with a standard, then only apply parts of that standard where you see fit, how does someone else know your changes. My point is that standards are developed for ease in communicating things without having to send out a book of design rules with evey print you send out.

If you say your drawing complies, then make them comply.

If your CAD system doesn't have built-in rules for compliance with Y14.5, then lobby them to do so. The 2 systems that I have most experience with both claim to fully support Y14.5 and priduce drawing to that standard. Yes, you can override the settings in both packages.
 

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

RE: Question, What is the difference between A & B?

Interesting Posts PaulJackson and Jim Sykes

I see your point about the basic 4 hole pattern having perfect form.  I would be in 100% agreement if the drawing showed a pattern that was 32.00mm square (41.00-9.00).

But in example (A), if the pattern can float, how would you tell how much it could float, and from where?  Without referencing B and C in the feature control frame, and without specifying their order, how could you constrain any more than two rotational and one locational degree of freedom on the DRF that are locked in by Datum A?

I'm not saying you are incorrect.  I'm just asking how do you measure off the datum reference frame for the two 9.00mm dimensions, when you don't have sufficient information to constrain the part on such a DRF in the first place?  I guess what I'm saying is, I'm not sure with example (A) that I could correctly orient the pattern to the rest of the part in accordance with the basic dimensions shown.

That's why I came to my conclusion in the earlier post.  But when once you mention it, I'm not so sure.

As an aside, a better way would be to box the 50.00 dimensions, assign an all around surface profile tolerance relative to datum A, then all the features of the part could be constrained to a DRF once for all features, for best effect.

I'd be interested in hearing your input.

Martin Smith
GDTP-S
 

RE: Question, What is the difference between A & B?

Quote:

I see your point about the basic 4 hole pattern having perfect form.  I would be in 100% agreement if the drawing showed a pattern that was 32.00mm square (41.00-9.00).
It does! Everything is there... "4X" declares the pattern, the FCF declares the type of control, and the datum feature(s) specified reveal which degrees-of-freedom are constrained (translation in Z, and rotation about the X and Y axes). It is not necessary for the designer to show the 32 X 32 basics as long as they can be equivalently derived from those given to relate the features according to the FCF (although I recommend that they do because inspection has to construct basics oriented to the features they are measuring to do the inspection even if the lazy designer snapped an XYZ endpoint on the axis of an angled hole).  

Quote:

But in example (A), if the pattern can float, how would you tell how much it could float,  and from where?
Is the pattern floating relative to the edges of the part or are the edges of the part floating relative to the pattern? Certainly if the part edges breech the patterned hole edges then they have gone too far! Maybe one could declare the pattern [B] and control the profile of the part edges to fix that. I think that I would figure out what functionally locates and orients what and consider controlling features likewise because that is what the assembly has to bare.

Quote:

Without referencing B and C in the feature control frame, and without specifying their order, how could you constrain any more than two rotational and one locational degree of freedom on the DRF that are locked in by Datum A?
You can't!

Quote:

I'm not saying you are incorrect.  I'm just asking how do you measure off the datum reference frame for the two 9.00mm dimensions, when you don't have sufficient information to constrain the part on such a DRF in the first place?  I guess what I'm saying is, I'm not sure with example (A) that I could correctly orient the pattern to the rest of the part in accordance with the basic dimensions shown.

MechNorth said,

Quote:

the two callouts (A) and (B) are in conflict, as (A) is not a refinement of (B); they both have the same tolerance of 0.2 on position (ignoring the preceding point about absence of diameter symbol), and both refer to the same four features.  Thus, they are in conflict.
True! If they were to coexist... scenario A should be a functionally required refinement of the pattern... if not eliminate it. If the holes functionally locate the edges eliminate scenario B's control... declare the pattern [B], as I said above, and tolerance the edges to the pattern.

You know we could be making a mountain out of a mole hill... ryandias just asked

Quote:

Can someone please explain the difference between callout A and callout B?


Quote:

As an aside, a better way would be to box the 50.00 dimensions, assign an all around surface profile tolerance relative to datum A, then all the features of the part could be constrained to a DRF once for all features, for best effect.
Sorry if I had remembered that you wrote this while I was typing my responses above I could have saved some keystrokes.

Paul
 

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