To put a stop to an argument...symmetry uses the same theory as Position, right? Symmetry of .005 has a zone of +/- .0025. The centerline of the feature you are comparing to the Datum's center line has to fall within that zone, right? I am getting the argument that symmetry lets the centerpoint be off center of the Datum's center by .005, not just half of that. Can someone clear this up for me? Thanks.

You are correct!

To put a stop to an argument...symmetry uses the same theory as Position, right? Symmetry of .005 has a zone of +/- .0025. The centerline of the feature you are comparing to the Datum's center line has to fall within that zone, right? I am getting the argument that symmetry lets the centerpoint be off center of the Datum's center by .005, not just half of that. Can someone clear this up for me? Thanks.

Thank you for the quick reply!

Hello all,
It seems my doubt is a little stupid, but I’m new in the job. I want to know if I’m measuring correctly the position/location dimensions. Please, see attached my file and analyse the formulas that I use to calculate measurement on item 17 (drawing inside file too). I had already sent several dimensional reports for our customers, and until now, none reject my report, but I’m not sure if my method is correct. If not, please explain how can I measure this kind of dimensions? For symmetry dimensions the procedure is the same?
In advance, thank you for your help.

Looks like I'm a little late to the dance on this one, but symmetry is more closely related to concentricity than it is to (true) position. Quoting from ASME Y14.5M 1994, 5.14: "...symmetry and concentricity controls are the same concept, except as applied to different part configurations." Because concentricity is sometimes called out when position makes more sense, the same probably applies to symmetry in your case. The symmetry tolerance does apply equally apportioned about a datum center plane as you suggest. Like concentricity, symmetry always applies on an RFS basis, whereas position may take feature size into account.

Hello all,
It seems my doubt is a little stupid, but I’m new in the job. I want to know if I’m measuring correctly the position/location dimensions. Please, see attached my file and analyse the formulas that I use to calculate measurement on item 17 (drawing inside file too). I had already sent several dimensional reports for our customers, and until now, none reject my report, but I’m not sure if my method is correct. If not, please explain how can I measure this kind of dimensions? For symmetry dimensions the procedure is the same?
In advance, thank you for your help.

Hello-

You might want to have a look at my response to the OP in this thread with regard to symmetry callouts. Your attachment doesn't seem to be providing enough information, though. How are you actually measuring the parts?

To put a stop to an argument...symmetry uses the same theory as Position, right? Symmetry of .005 has a zone of +/- .0025. The centerline of the feature you are comparing to the Datum's center line has to fall within that zone, right? I am getting the argument that symmetry lets the centerpoint be off center of the Datum's center by .005, not just half of that. Can someone clear this up for me? Thanks.
Not exactly.

Position can be used at RFS (Regardless of Feature Size), MMC (Maximum Material Condition), and even LMC (Least Material Condition). Symmetry is always RFS. Position controls the axis or centerplane of the perfect geometric counterpart of the produced feature. Symmetry (and Concentricity) center features by taking the differential opposing surface point locations.

NetScorpium

I don't see a BASIC from -A-. The BASIC from -B- goes to a point. The angular offset is from no Datum.

From the view you've attached, I don't see how to measure the TP as called out without using some "healthy" assumptions (almost always will get me in trouble). Perhaps there is more information on the rest of the drawing?

OOPS!!

Must have posted just as JSW05 was. At least we're saying the same thing :agree1:

Hello JSW05,
Thank you for your answer. I had improve the file in order to explain better my doubt. Please look again.

Hello Bill,
Thank you for your answer. About your question... look my reply above to JSW05.

Hello JSW05,
Thank you for your answer. I had improve the file in order to explain better my doubt. Please look again.

I'm not sure what you're asking. It appears that your method of calculating the position callout in your attachment is correct; did you also need information about the concentricity callout?

Hello JSW05,
The main target of my post is ensure that my measurement method for calculating the position callout and concentricity callout is the most correct. Please, analyse my method to measure the concentricity too, and tell me your opinion.

Hello JSW05,
The main target of my post is ensure that my measurement method for calculating the position callout and concentricity callout is the most correct. Please, analyse my method to measure the concentricity too, and tell me your opinion.

Because of the difficulties involved in actually measuring concentricity error, I'm not sure where your data is coming from. In my experience, in almost every instance I've ever seen where concentricity was specified it was really control of position or runout that was needed. The input values for your formula must be the result of measurement for the median points of diametrically opposed elements of the feature being controlled. In practical terms, this involves using two indicators positioned 180 degrees apart on the controlled feature, and determing the net difference in the readings at different points along the feature, and then identifying the worst case, which is the greatest net difference between any two readings. Thus it appears that perhaps your formula may be as simple as finding the difference between two (perhaps differently signed) values.

If this isn't clear, or if I haven't answered your question, please post back and I'll give it another go.

JSW05 has addressed your question on concentricity. Now for position.....

The calculation for position is useage of the Pythagorean Theorem (and multiply by 2). From the values I see you have reported (0.21 from basic and .05 from basic), I get a position of .432. Does that coincide with what you get?

JSW05 has addressed your question on concentricity. Now for position.....

The calculation for position is useage of the Pythagorean Theorem (and multiply by 2). From the values I see you have reported (0.21 from basic and .05 from basic), I get a position of .432. Does that coincide with what you get?

Hi Bill

I get the same answer as you, so I was in error in my other response to the OP, when I apparently read 0.21 as .021 :bonk: . Interestingly, that error results in the same number as in the example spreadsheet (0.11), so it does look like there's a problem.

JSW05 has addressed your question on concentricity. Now for position.....

The calculation for position is useage of the Pythagorean Theorem (and multiply by 2). From the values I see you have reported (0.21 from basic and .05 from basic), I get a position of .432. Does that coincide with what you get?
Humm... well if I understand your calculation formula for position, the 0.432 is the result of:

Formula: *** h^2=[(C1)^2 + (C2)^2]
*** FinalResult=(h^2) * 2

Applying formula:
h^2=(50.00-49.79)^2 + (50.00-49.95)^2
h^2=0.0441 + 0.0025
h=0.216

FinalResult=0.216 * 2 = 0.432

OK, this I understand. And if I have only one plan
Example: |PositionSymbol|Ø 0.1|A|

or if I have tree plans
Example |PositionSymbol|Ø 0.1|A|B|C|

The Pythagorean Theorem (and multiply by 2) is the same to calculate these kind of positions? How? Where can I find more information about position and concentricity calculations?

Because of the difficulties involved in actually measuring concentricity error, I'm not sure where your data is coming from. In my experience, in almost every instance I've ever seen where concentricity was specified it was really control of position or runout that was needed. The input values for your formula must be the result of measurement for the median points of diametrically opposed elements of the feature being controlled. In practical terms, this involves using two indicators positioned 180 degrees apart on the controlled feature, and determing the net difference in the readings at different points along the feature, and then identifying the worst case, which is the greatest net difference between any two readings. Thus it appears that perhaps your formula may be as simple as finding the difference between two (perhaps differently signed) values.

If this isn't clear, or if I haven't answered your question, please post back and I'll give it another go.
Yes, I understand your explanation. To measure concentricity, I use a Coordinate Measuring Machine. For example, I measure a diameter and the median points of diametrically are placed to 0,0 (X=0,Y=0). Than I measure the other diameter and I calculate the distance between the two median points of diametrically. The result is my concentricity value.

The Pythagorean Theorem (and multiply by 2) is the same to calculate these kind of positions? How? Where can I find more information about position and concentricity calculations?
Yes, the calculation works for one, two, or three variables.

Just about any book on Geometric Dimensioning and Tolerancing will go into detail about Concentricity and Position, as well as all other symbols. A few I'll mention are "ANSI Y14.5", "Geometrics" by Lowell Foster, "Geometric Dimensioning and Tolerancing" by James Meadows, "Geometric Dimensioning and Tolerancing" by Al Neumann. You also might try "Googling" the term GD&T (or spelled out) and see what pops up.

Yes, I understand your explanation. To measure concentricity, I use a Coordinate Measuring Machine. For example, I measure a diameter and the median points of diametrically are placed to 0,0 (X=0,Y=0). Than I measure the other diameter and I calculate the distance between the two median points of diametrically. The result is my concentricity value.

It sounds like you're measuring runout or position, not concentricity. In order to accurately measure concentricity you have to be able to rotate the part about the datum axis using diametrically opposed indicators as I advised before. It could very well be that the result your're getting will satisfy design intent, however. As I also said earlier, it's been my experience that when concentricity is specified it's usually by someone who understands the everyday definition of the word (two things that are coaxial) but isn't aware that it isn't that simple in the GD&T sense.