I have seen a number of drawings where a hole ends up with a larger tolerance east-west than north-south, so rather than expand the diametrical tolerance to cover both, I see two reference linear dimensions with separate control frames. (See top example) I was wondering if possible to combine these into two single segment control feature controlf frames on the diameter dimension. (See bottom example). Is this allowed and is it clear?
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2 Single Segment FCF to make Rectangular Tolerance Zone? 3
- Thread starter JasonSp
- Start date
To my interpretation, the first example has no interpretation possible under ASME or ISO. The second example actually is a reference to a composite pos tol, which precludes its use in this manner.
To use positional tolerancing with an elliptical zone, you'll have to completely describe your pos tolerance zone within the content of the drawing.
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
To use positional tolerancing with an elliptical zone, you'll have to completely describe your pos tolerance zone within the content of the drawing.
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
The top one doesn't explicitly match any example in 14.5M-1994 that I'm familiar with but I'm inclined to say the intent is clear. You've dimensioned it like you would a slot or similar. It's probably how I would have attempted to dimension the case you state, I may have left the dia symbol on the ref dims, not sure.
I think the second example is not composite positional tol but (incorectly applied) "multiple single-segment' FCF, or at least looks like it so is definitely wrong for your intent. (See 5.4.1.8 of ASME Y14.5M-1994 for disambiguation from composite).
So in summary, I'd say your second option is wrong and unclear.
Similar came up in a recent thread though I don't recall much detail being given. There are a few very knowledgable members who seem to enjoy extrapolate from what the standard says, maybe they'll chime in.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
I think the second example is not composite positional tol but (incorectly applied) "multiple single-segment' FCF, or at least looks like it so is definitely wrong for your intent. (See 5.4.1.8 of ASME Y14.5M-1994 for disambiguation from composite).
So in summary, I'd say your second option is wrong and unclear.
Similar came up in a recent thread though I don't recall much detail being given. There are a few very knowledgable members who seem to enjoy extrapolate from what the standard says, maybe they'll chime in.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
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2
- #4
The first drawing is called a "bi-directional" positional tolerances since the tolerances are not equal in both the X and Y axis. This is used a lot on slots where the length of the slot usually has more tolerance than the widthand is covered by ASME Y14.5M-94 section 5.9 page 135.
The second example reflect 2 single segment feature control frames on the same feature. They relate different tolerances to different datums. There are two (2) requirements here.
Dave D.
The second example reflect 2 single segment feature control frames on the same feature. They relate different tolerances to different datums. There are two (2) requirements here.
Dave D.
Well done Dingy,
JasonSP, figure 5-41 page 139 referenced from within the reference Dave gave shows what you are trying to achieve, it doesn't have the reference dimensions shown but is otherwise similar to what you have.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
JasonSP, figure 5-41 page 139 referenced from within the reference Dave gave shows what you are trying to achieve, it doesn't have the reference dimensions shown but is otherwise similar to what you have.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
- Thread starter
- #6
My comment was presuming an elliptical zone. Sorry for the misinformation.
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
I believe the first example to be acceptable and proper. However a close examination indicates that 'physical identification' of the datum features might just be in order.
It would provide maximun latitude for locating the hole while cproviding a control for the edge distance.
It would provide maximun latitude for locating the hole while cproviding a control for the edge distance.
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1
- #9
powerhound
Mechanical
The top example is good but the bottom example is not. To use single segment FCF you still have to abide by the same rule as in composite, the top segment must have a larger value than the bottom. The top segment should read "position within a diameter of 0.5 to A, B, and C - the bottom segment should read "position within a diameter of 0.2 to A and B." This will give you more tolerance in one direction than the other but the full zone won't be rectangular like the top example. It will be more like a small cylindrical zone positioned within a larger cylindrical zone and the small zone can move within the larger zone from left to right only, not up and down. Depending on your application, you can use the top example on your drawing, or change the bottom example to what I've recommended and you will have a legal callout.
Here are 2 links on the subject that really helped me when I was struggling with the concept.
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
Here are 2 links on the subject that really helped me when I was struggling with the concept.
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
powerhound
Mechanical
ringster,
What do you mean? I see all the relative datums identified and the feature being controlled is shown with basic dimensions from their respective datums.
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
What do you mean? I see all the relative datums identified and the feature being controlled is shown with basic dimensions from their respective datums.
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
Powerhound,
The standard contains only one sentence as I recall with regards to Physical Ident of Datum Features. Given a symmetrical part, it becomes necessary to mark the part physically by 'some means' to assure that everyone is using the same datum reference frame.
Par 4.2 of the 1988 Standard.
Too often overlooked in my opinion.
The standard contains only one sentence as I recall with regards to Physical Ident of Datum Features. Given a symmetrical part, it becomes necessary to mark the part physically by 'some means' to assure that everyone is using the same datum reference frame.
Par 4.2 of the 1988 Standard.
Too often overlooked in my opinion.
I agree that the second example is incorrect. It is trying to say the same as the first with a bi-directional tolerance.
One can have two single segment feature control frames referencing different datums but not in this case. It's just wrong.
Dave D.
One can have two single segment feature control frames referencing different datums but not in this case. It's just wrong.
Dave D.
I wouldn't go as far as to say that the second example is wrong, but it definitely doesn't match the intent. The second example would amount to a bi-directional zone, but the directions would be skewed if there was any perpendicularity error between B and C. The tolerance zone would be a parallelogram shape, with a different angle on every part.
In the first example, one could argue that in the FCF for the vertical direction the C reference should be omitted. It doesn't do anything.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
In the first example, one could argue that in the FCF for the vertical direction the C reference should be omitted. It doesn't do anything.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
A couple other points to consider are:
1) the Dia 30 size needs a tolerance somewhere for it to be a feature of size, and therefore locatable by a position control
2) the (30) ref dimension with each of the position controls is not necessary, and conflicts with the Dia 30 dimension as it purports a linear rather than cylindrical feature
Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
1) the Dia 30 size needs a tolerance somewhere for it to be a feature of size, and therefore locatable by a position control
2) the (30) ref dimension with each of the position controls is not necessary, and conflicts with the Dia 30 dimension as it purports a linear rather than cylindrical feature
Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
aardvarkdw
Mechanical
ASME Y14.5M-1994, 5.9
"Where it is desired to specify a greater tolerance
in one direction than another, bidirectional positional
tolerancing may be applied. Bidirectional positional
tolerancing results in a noncylindrical tolerance zone
for locating round holes; therefore, the diameter symbol
is omitted from the feature control frame in these
applications."
I believe that figure 5-41 is actually incorrect per the text of section 5.9 as it shows diameter symbols in both FCFs when the text clearly states that they should be omitted.
Correct me if I am misreading this.
David
"Where it is desired to specify a greater tolerance
in one direction than another, bidirectional positional
tolerancing may be applied. Bidirectional positional
tolerancing results in a noncylindrical tolerance zone
for locating round holes; therefore, the diameter symbol
is omitted from the feature control frame in these
applications."
I believe that figure 5-41 is actually incorrect per the text of section 5.9 as it shows diameter symbols in both FCFs when the text clearly states that they should be omitted.
Correct me if I am misreading this.
David
aardvark ... the Fig. 5-41 that I'm looking at doesn't have a diameter symbol in the tolerance section of the two position FCFs. The feature is a cylindrical hole, so a diameter symbol belongs on the size callout. The orientation of the axis of the hole is a refinement of the rectangular positional tolerance zone (i.e. floats within it), and it's ok to have a cylindrical orientation tolerance zone within a rectangular positional tolerance zone. No problem with 5-41.
Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
aardvarkdw
Mechanical
Allow me to pull my foot out of my mouth.... I saw the position tolerance symbol and for some reason my mind read diameter. I even reread it before I hit the post button to make sure I was not seeing things... I'll just blame Lysdexia and leave it at that... sorry.
David
David
My copy of 14.5M-1994 doesn't have dia symbols on the FCF either.
I'm kind of wondering why we're still debating this though, seems to me the OP got the answer they needed from Dingy yesterday and the OP replied acknowledging it.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
I'm kind of wondering why we're still debating this though, seems to me the OP got the answer they needed from Dingy yesterday and the OP replied acknowledging it.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
Dingy,
Im not sure that the fact different tolerances are used has a bearing, or is necessary to apply the technique. I believe they could have correctly been the same and resulted in a square zone rather than a rectangular.
I feel slighted that I did not get a STAR for mentioning Physical Datum Feature Identification. :>(
Im not sure that the fact different tolerances are used has a bearing, or is necessary to apply the technique. I believe they could have correctly been the same and resulted in a square zone rather than a rectangular.
I feel slighted that I did not get a STAR for mentioning Physical Datum Feature Identification. :>(
powerhound
Mechanical
As I said in my previous post, the bottom example is incorrect because the top value is smaller than the bottom value. You can't do it using composite position and you can't do it using single segment.
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
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