Hi everyone:
I have come accorss a rather strange DATA SHEET in which all the measured values of a part(s) are exactly the same as the measured values of the other operators..!

Here's a Brief description of the DATA SHEET below.

PART = 2x2 Inch FOAM piece. LSL = 2.000 Inch ; USL = 2.250 Inch;
No. of parts = 5; No. of Trials = 3; No. of Operators = 3;
Measured Characteristc - Length; Gage Name - RULER; Gage Number - 1/16 Inch = 0.0625 Inch

PS. Images of the GRR Data sheets are attached for reference (Click on the Images for Bigger size)

http://img151.echo.cx/img151/3844/grr14ha.th.png (http://img151.echo.cx/my.php?image=grr14ha.png) http://img151.echo.cx/img151/5382/grr20bu.th.png (http://img151.echo.cx/my.php?image=grr20bu.png)

From the above Data sheets:
- There is NO Equipment variation (Zero);
- NO Appraiser/Operator variation (Zero) [This is not possible unless Assuming all the operators measure the part together influencing each others readings..!];
- R&R is also Zero;

-- There is only Part Variation = 0.131 and %PV = 52.4

In this Case Study I'd like to know:

Q. Referring to the above GRR Study; What would one should change to Improve the Measurement System..?

Q. If GRR Study is to be repeated; What would one do differently (Assuming all operators measured the part together)..?


:thanx:

From the above Data sheets:
- There is NO Equipment variation (Zero);
The device is a scale (ruler); why does this surprise you?
- NO Appraiser/Operator variation (Zero) [This is not possible unless Assuming all the operators measure the part together influencing each others readings..!];
Of course it's possible, given the device and the object being measured, and assuming reasonably competent operators.
Q. Referring to the above GRR Study; What would one should change to Improve the Measurement System..?
It appears that the device lacks the requisite sensitivity; the tolerance spread is .250 and the resolution of the device is (apparently) .0625. In order to be kosher, the device should be sensitive to 1/10 of the tolerance spread (.025 in this case). If you were to use calipers instead of a scale you would undoubtedly see more of the variation you're looking for.
Q. If GRR Study is to be repeated; What would one do differently (Assuming all operators measured the part together)..?
See the answer to #1.

The device is a scale (ruler); why does this surprise you?
It does bother me a little bit because a ruler whose precison is 0.0625 Inch (which is very high and the ruler cost is cheap); What is the necessity that ruler has the exact accuracy throughout the length of the ruler and the operators using it to measure the part might not use the same/exact position(s) of the ruler always..!
Of course it's possible, given the device and the object being measured, and assuming reasonably competent operators.

Resonable competent operators will have very very less variation but is it possible to have no variation..? Don't you think that the Operators measuring the part influenced each other's readings..?
It appears that the device lacks the requisite sensitivity; the tolerance spread is .250 and the resolution of the device is (apparently) .0625. In order to be kosher, the device should be sensitive to 1/10 of the tolerance spread (.025 in this case). If you were to use calipers instead of a scale you would undoubtedly see more of the variation you're looking for.

[/color]See the answer to #1.
Yes, I too came up with the same conclusion that:

- The Gage (Scale or Ruler) used to measure the part (Foam piece) is not right since unit of measurement should atleast be:
1/10 of the Tol (0.250) = 0.0250 but it actually is 0.0625

- But when I do XbarR Analysis: The Precision to Tol ratio = 0 (** P/Tol < 0.1 - Adequate Measurement system; P/Tol>0.3 - Unaccepatable Measurement system).

So this states that measurement system used is Adequate...!!..?? (I'm totally confused here.. :frust: )

Yes, I too came up with the same conclusion that:

- The Gage (Scale or Ruler) used to measure the part (Foam piece) is not right since unit of measurement should atleast be:
1/10 of the Tol (0.250) = 0.0250 but it actually is 0.0625

- But when I do XbarR Analysis: The Precision to Tol ratio = 0 (** P/Tol < 0.1 - Adequate Measurement system; P/Tol>0.3 - Unaccepatable Measurement system).

So this states that measurement system used is Adequate...!!..?? (I'm totally confused here.. http://elsmar.com/Forums/images/smilies/frustrated.gif )But you've already determined that the device is not sensitive enough to reveal possible issues in the system. There's no point in going further, because at this point that are only a few possibilities:

The tolerance is too tight (while 1/4" might seem generous, sometimes a tolerance like that will be assigned arbitrarily).
There's actually danger of approving nonconforming material, (i.e., the tolerance is appropriate) so a more sensitive device is needed.

But you've already determined that the device is not sensitive enough to reveal possible issues in the system. There's no point in going further, because at this point that are only a few possibilities:

The tolerance is too tight (while 1/4" might seem generous, sometimes a tolerance like that will be assigned arbitrarily).
There's actually danger of approving nonconforming material, (i.e., the tolerance is appropriate) so a more sensitive device is needed.

You mean Tolerance is not appropriate assuming that it is too tight and assigned arbitrarily..?

Below is the Sigma Product Vs Sigma Total Graph which shows the distribution a little bit skewed to left; Only some part of the distribution is going below LSL (2.000 Inch in this case).

http://img94.echo.cx/img94/7108/sigmap8fu.png

This graph shows that there are/will be parts out of spec (2.000-2.250) but not in large quantity.

Q. So how does it has more danger of approving nonconforming material with respect to this graph..?

:thanx:

You mean Tolerance is not appropriate assuming that it is too tight and assigned arbitrarily..?
I don't know whether the tolerance is appropriate or not. That's what you need to find out, if you don't already know.

Below is the Sigma Product Vs Sigma Total Graph which shows the distribution a little bit skewed to left; Only some part of the distribution is going below LSL (2.000 Inch in this case).
Where did you get the data needed for the graph? Using the inadequately-sensitive device? Please go back and look at the two points in my last post.
BTW, the distribution in the image is shifted, not skewed.

What is the risk if the parts are a tiny bit out?

What is the likelihood that they would be way out of spec?

It seems to me that you are putting far more effort into this project than you have to. Why not just make some attribute (go / no go) gage up, and chart nothing. Your scale (ruler) discriminates to 1/16", and your spec is 1/4" which is 1 to 4. So it is practically a go/no go check anyway.

This also seems a prime candidate for some error-proofing device.

I don't know whether the tolerance is appropriate or not. That's what you need to find out, if you don't already know.

Where did you get the data needed for the graph? Using the inadequately-sensitive device? Please go back and look at the two points in my last post.
BTW, the distribution in the image is shifted, not skewed.
The Data sheets are attached as thumbnails in the first post itself. And by meaning "inadequately-sensitive device" (RULER), yes.

I do agree 100% with you that the device used for measuring the part is not sensitive enough to measure the part close to its true value.

Q. So how can I determine that the Tol is appropriate or not..? Sorry, I do not know how Tol can be verified since this is just a case study not a actual manufactured part whose Tol can be verified.. :confused:

What is the risk if the parts are a tiny bit out?

What is the likelihood that they would be way out of spec?

It seems to me that you are putting far more effort into this project than you have to. Why not just make some attribute (go / no go) gage up, and chart nothing. Your scale (ruler) discriminates to 1/16", and your spec is 1/4" which is 1 to 4. So it is practically a go/no go check anyway.
Q. How do you determine that this part is suitable for a go/no go check..? Are there any specific ratios (1:4 in this case) to determine that..?

And also the Part in this case is a peice of "Foam" (2x2 Inch). If the part is held even in hand for measuring, the shape of the part is modified giving a different dimension value..!!

Q. So how can it be used for a Go/no go check when the shape of the part measured is altered..?

* The best way to measure the part (Foam) might be drwaing the shape profile around the the characteristc being measured and then measure the dimensions (or)

* Placing the object on a shawdow projector that projects the shape (Characteristic being measured) of the part to a scale and then measuring the shadow with respect to scale.
This also seems a prime candidate for some error-proofing device.
Q. You mean to say that scale (Ruler) needs to be calibrated..?

:thanks:

Q. So how can I determine that the Tol is appropriate or not..? Sorry, I do not know how Tol can be verified since this is just a case study not a actual manufactured part whose Tol can be verified.. :confused:
You need to tell us what the assumptions are if the question is hypothetical. Where did the case study come from?

You need to tell us what the assumptions are if the question is hypothetical. Where did the case study come from?
What assumptions you want to know..?

This is a "Class Case Study" given to students taking up a 'Quality Program'.
The parts (2x2 Inch - Foam) were provided to students for measuring with a 1/16 Inch ruler. The Tolerance (2.000-2.250 Inch) provided in this case, I assume it to be arbitarirly provided by the professor since I cannot verify it..!

But I like to know 2 situations:
1. If the Tol. is actual specification (Specified Tol.) of the manufcactured part (2x2 Inch Foam)?
2. If the Tol. is hypothetical assigned by the Prof. for the students to do the Gage R&R study?

What assumptions you want to know..?
When you present a hypothetical situation, "assumptions" are information assumed to be true that's needed to understand the situation and properly evaluate the question. In this case, you should have just given us the question/situation as it was presented to you.

But I like to know 2 situations:
1. If the Tol. is actual specification (Specified Tol.) of the manufcactured part (2x2 Inch Foam)?
2. If the Tol. is hypothetical assigned by the Prof. for the students to do the Gage R&R study?
I'm not sure it's important; it seems that for purposes of the case study you're probably supposed to accept the tolerance as appropriate, or maybe not-- maybe you'll get extra credit for questioning it:cool: .

[/color]
When you present a hypothetical situation, "assumptions" are information assumed to be true that's needed to understand the situation and properly evaluate the question. In this case, you should have just given us the question/situation as it was presented to you.
OK here are the exact Questions that I have with me which I posted in the first post only. But I will repeat it again without my conclusion or assumptions.. :)
==================================================================
Q1. Referring to the above GRR Study; What would one should change to Improve the Measurement System..?

Q2. If GRR Study is to be repeated; What would one do differently..?

Assumption/Information - All operators measured all the parts (5 parts in this case) Individually but in a group with same ruler (Each part measured 3 times - 3 Trials).
==================================================================
I assumed that since all the operators measured all the parts but since every reading was eaxctly the same as each other (Taking ruler accuracy into account, the way the part was measured); all these things influenced each others measurement observation including the measured values..!!

So the Answer to the Q2 would be:

* Use a more accurate or resolution sensitive instrument Eg. Vernier Caliper, which has a resolution 10% of the Tol.(0.250) i.e., 0.0250 would give a better Repeatability(Equipment Variation) results.... I'm confused here or am I right..?

* The (5)parts should have been measured by all the (3)operators individually rather than in group to avoid the influence factor and get better Reproducability(Appraiser Variation).

Are the above two conclusions correct? Anything more could be added to it?

Answer for the Q1. As you Quoted earlier -

* It appears that the device lacks the requisite sensitivity; the tolerance spread is .250 and the resolution of the device is (apparently) .0625. In order to be kosher, the device should be sensitive to 1/10 of the tolerance spread (.025 in this case). If you were to use calipers instead of a scale you would undoubtedly see more of the variation you're looking for.

Anything else, that can be added for Q1 answer..?
==================================================================

Sorry about all these question but I am not able to draw any more conclusions on -

How the Measurement system can be improved.. :confused:
What could be done differently if the Gage R&R is repeated.. :confused:

:thanx:

You've told us nothing about the protocol for the test, other than the operators were in "a group." If that's all the information you were given, then the answers you have now should suffice. Let us know how it turns out.

You've told us nothing about the protocol for the test, other than the operators were in "a group." If that's all the information you were given, then the answers you have now should suffice. Let us know how it turns out.
I'm sorry, I didn't get you. What protocol (Information) are you talking about..?
Please explain.. :rolleyes:

EDIT:
The other Info. I have is:

- That the part (Foam) is always measured at a Pre-determined/pre-marked area on the foam (i.e., about the centre of the part; characteristic measured is length/side of the foam).

- First all the 5 parts are measured by Operator 1 once (Trial 1 of 1st operator) and then the second operator measures all 5 parts once (Trial 1 of 2nd Operator) and then the third operator measures all 5 parts once (Trial 1 of 3rd Operator). The same pattern is followed for the 3 Trails by 3 Operators.

I'm sorry, I didn't get you. What protocol (Information) are you talking about..?
Please explain.. :rolleyes:

EDIT:
The other Info. I have is that the part (Foam) is always measured at a Pre-determined/pre-marked area on the foam (i.e., about the centre of the part; characteristic measured is length/side of the foam)
ZeeTX, we don't seem to be headed in any particular direction here.:truce: Maybe that's my fault. As far as "protocol" is concerned, I was referring to a formal plan for testing or experimentation; a protocol describes how testing is to be conducted and the associated controls. I'm not sure it matters at this point, though. I think your original questions have been answered, but if not, please ask again after reading through the thread.

ZeeTX, we don't seem to be headed in any particular direction here.:truce: Maybe that's my fault. As far as "protocol" is concerned, I was referring to a formal plan for testing or experimentation; a protocol describes how testing is to be conducted and the associated controls. I'm not sure it matters at this point, though. I think your original questions have been answered, but if not, please ask again after reading through the thread.
No, Not at all. Its been a pleasure going through the discussion of this case study. Though I am still not that satisfied that there aren't any more conclusions that could be drawn from the GRR Info. I have.. :bonk:

Anyway, I'll go through the thread once again and see if I have anything more that needs more clarification and let you know by tomorrow.

Once again thank you very much JSW05, for bearing and being with me.. :agree1:

:thanx:

Has anyone else any difference of opinion or drawn further conclusion(s) for the 2Qs. from the above Case Study..?
What is the risk if the parts are a tiny bit out?

What is the likelihood that they would be way out of spec?

It seems to me that you are putting far more effort into this project than you have to. Why not just make some attribute (go / no go) gage up, and chart nothing. Your scale (ruler) discriminates to 1/16", and your spec is 1/4" which is 1 to 4. So it is practically a go/no go check anyway.

This also seems a prime candidate for some error-proofing device.
Can the part(foam) be measured by a Go/no-go guage check..? If yes, how accurate the measured value might be..?

How the Measurement system can be improved..?
What could be done differently if the Gage R&R is repeated..?

Interesting...I'll take a shot at this.
(You probably already know this, but) Some suggestions are:

1. Develop a standard method for measuring the parts. Train all operators to use this method. Ensure that they understand and follow the method correctly.
2. If possible, develop some kind of a holding fixture for the piece of foam, so as to reduce the 'handling' effect.
3. Ensure that the parts taken for the study truly cover the spec range.
4. If possible, get a ruler with graduations finer than 1/16".
5. If not, ask the operators to record the readings by 'estimating' between graduations.
6. Do a 'blind' study so operators do not know each other's readings or their own previous reading for the part.
7. Randomize the sequence of the parts being measured.

Does this help?

The device is a scale (ruler); why does this surprise you?

Of course it's possible, given the device and the object being measured, and assuming reasonably competent operators.

[color=black]It appears that the device lacks the requisite sensitivity; the tolerance spread is .250 and the resolution of the device is (apparently) .0625. In order to be kosher, the device should be sensitive to 1/10 of the tolerance spread (.025 in this case). If you were to use calipers instead of a scale you would undoubtedly see more of the variation you're looking for.

See the answer to #1.

Hi Jim...I was wondering where you got the 1/10 of tolerance # from. Is it a published standard? or is it something just commonly used?

Thanks!!

Hi Jim...I was wondering where you got the 1/10 of tolerance # from. Is it a published standard? or is it something just commonly used?

Thanks!!

Have a look here (http://elsmar.com/Forums/showthread.php?p=151944#post151944); Hershal just gave an excellent answer.