Back to Basics Statistics - Standard Deviation small when performing an R&R

Govind

Super Moderator
Staff member
Super Moderator
#11
Jsatain1,
The first thing caught my eye even before looking into your summary result is the
"The number of distinct categories=1"
You should be having 5 or more categories to be able to detect variation in processes and detect any special cause variations.
You may be having equipment discrimination issues.
See Page 19,20 of AIAG MSA Manual Second edition for details.
Also see Page 5 section 2 subclause 4 (thumb rule).
Regards,
Govind.
 
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D

Darius

#12
Jstain1, you are. I always like to wach the % of variation, and it's too big (more than 40% of variation depends on operator and trials, you have to work with repeatibility and reproducibility).

---
Sam

Tertuliano was one of the first Christian figures, his name was Quinto Septimio Florencio Tertuliano and born in Cartago in 150-160 and became Christian at 195 A.C.

He wrote:

Facilius est pro castitate, quam cum castitate mori.
You can translate from Latin literaly:

It's easer to die because of chastity than to die in chastity.

or a more liberal translation.

If I don't try to answer any question or to correct the wrong answers, it's more possible that I don't do any failures (nor gramatical or because of faulty knoledge).

or as I put in my posts (from the Havamal, old escandinavian book, the sayings of the gods)

"Vits er thorf, theim vitha ratar; daelt er heima hvat; at augabragthi verthr, sá er ekki kann ok med snotrom sitr."

Sorry about my English, as Mark Twain said ones "Begabte menschen können jedoch in dreißig jahre deutsch lehren.", the same with other languages, and English is not my mother language (nieder die deutche sprache).

:rolleyes:
 
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J

Jstain1

#15
Lost in OZ

Steve Prevette said:
Two things that haven't been brought up yet:

1. What is the time series of the data? We can have a fine looking CI, fine looking standard deviation, but if the data are showing a trend (ie NOT STABLE), then it is meaningless.

2. To judge if the R&R spread is acceptable (assuming the data were statistically in control), you really need to know the application the gage is being used for. If the gage readings actually did vary as much as the R&R is telling you, what are the cost effects of that? Will parts that are outside of specification potentially fail to be detected because the gage is too sloppy? Even if in spec, will parts no longer fit together well enough? Or is this a case of "close enough" as in playing horseshoes (or hand grenades)?
This is the question, apparently we've placed several thousand parts on hold from the vendor becase a sampling of them has failed to pass our accepatance testing through the ATE's. So my thoughts are to perform an R&R.

My hope was to see where they were statiscaly.

I know they are calibrated, and within the performance as set by the manufacture.
I know that the unceratainty associated is well within a 4 to 1.
The product passed the vendors EOL testers, and the data they captured has a delta from our data which indicates one of our process or gage is suspect.

I conducted an R&R as i've described earlier in this thread and got the results I've mentioned. So now I'm trying to convince they people involved that the ATE's here are suspect, and not so much the vendors. FYI, the ate's we have are very out of date, whereas the vendors are state of the art.

I intend on doing another R&R on both mine, and the vendor volunteered to participate as well. (Great vendor)

I intend to use three ATE's, five parts, there trials.
 
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