Elsmar Cove Forum Header Graphic The Elsmar Cove Wiki More Free Files The Elsmar Cove Forums Discussion Thread Index Post Attachments Listing Failure Modes Services and Solutions to Problems Elsmar cove Forums Main Page Elsmar Cove Home Page
Miner's MSA (Measurement Systems Analysis) Blog 
Go Back   The Elsmar Cove Forum > ISO (International Organization for Standardization) Standards > ISO 17025 - General Metrology, Measurement Device, Calibration and Test Laboratories > Gage R&R (GR&R) and MSA (Measurement Systems Analysis)
Forum Username

Wooden Line

What does the P/t ratio (Precision/Tolerance) =RR/(USL-LSL) say about my gage study?

Wooden Line
Search the Elsmar Cove
Search Elsmar
Monitor the Elsmar Forum
Follow Marc & Elsmar
Elsmar Cove Forum RSS Feed  Marc Smith's Google+ Page  Marc Smith's Linked In Page   Marc Smith's Elsmar Cove YouTube Page  Marc Smith's Facebook Page  Elsmar Cove Twitter Feed
Elsmar Cove Groups
Elsmar Cove Google+ Group  Elsmar Cove LinkedIn Group  Elsmar Cove Facebook Group
Donate and $ Contributor Forum Access
Courtesy Quick Links

Links that Elsmar Cove visitors will find useful in your quest for knowledge:

Howard's
International Quality Services
Marcelo Antunes'
SQR Consulting
Bob Doering's
Correct SPC - Precision Machining

NIST's Engineering Statistics Handbook
IRCA - International Register of Certified Auditors
SAE - Society of Automotive Engineers
Quality Digest Portal
IEST - Institute of Environmental Sciences and Technology
ASQ - American Society for Quality

Related Topic Tags
precision - tolerance ratio
Reply
 
Thread Tools Search this Thread Rate Thread Content Display Modes
  #1  
Old 13th October 2005, 09:30 AM
rderoeck - 2006

 
 
Posts: 7
Question What does the P/t ratio (Precision/Tolerance) =RR/(USL-LSL) say about my gage study?

Can somone explain to me what the P/t ratio (Precision/Tolerance) =RR/(USL-LSL) tells me about my gage study? Is there some magic number that needs to be met?

Thanks,
Rich DeRoeck

Sponsored Links
  #2  
Old 13th October 2005, 09:39 AM
Jim Wynne's Avatar
Jim Wynne

 
 
Posts: 14,077
Quote:
In Reply to Parent Post by rderoeck

Can somone explain to me what the P/t ratio (Precision/Tolerance) =RR/(USL-LSL) tells me about my gage study? Is there some magic number that needs to be met?

Thanks,
Rich DeRoeck
Welcome to the Cove

The precision/tolerance ration is a measure of how much of the tolerance is being consumed by gage error. The generally accepted goal is 0.1 or less (10%). Here's a basic explanation (scroll down):
http://www.itl.nist.gov/div898/handbook/glossary.htm#P
Thanks to Jim Wynne for your informative Post and/or Attachment!
Sponsored Links

  #3  
Old 13th October 2005, 11:16 AM
rderoeck - 2006

 
 
Posts: 7
So......this is diferent than the % R&R requirement of <10%. Do I have this right?

Rich
  #4  
Old 13th October 2005, 11:30 AM
Jim Wynne's Avatar
Jim Wynne

 
 
Posts: 14,077
Quote:
In Reply to Parent Post by rderoeck

So......this is diferent than the % R&R requirement of <10%. Do I have this right?

Rich
Well, more precisely, it's a different way of looking at it that takes the 3-sigma magnitude of R&R into consideration.
  #5  
Old 13th October 2005, 12:35 PM
Miner's Avatar
Miner

 
 
Posts: 3,540
There are an increasing number of ways to evaluate a measurement system, and each of these is intended to answer a different question about the suitability of the system.

If your question is "Is this gauge adequate to inspect a part to this tolerance?", then P/T ratio (known as % R&R before the proliferation of indicators) answers this question. The typical standard for P/T ratio is 10% or less is ideal, between 10% to 30% may be acceptable depending on the importance of the measurement, the cost of new gauging, etc., and > 30% is not acceptable.

If your question is "Is this gauge adequate to inspect a part as part of study (e.g., Six Sigma, DOE, capability, etc.)?", then %TV (Total Variation) answers this question. The standard is the same as above. In addition, the Number of Destinct Categories is used. An ndc >/= 5 is good, between 2 & 5 may be acceptable, and < 2 is unacceptable. Wheeler uses a Discrimination Ratio, which must be >/= 4, and requires the gauge resolution to be < the StdDev of PV (Part Variation).

If you want to know where the variation is coming from, % Contribution of each component answers this question.

See AIAG's MSA manual and/or Wheeler's "Evaluating the Measurement Process" for more information.
Thanks to Miner for your informative Post and/or Attachment!
  #6  
Old 13th October 2005, 01:49 PM
rderoeck - 2006

 
 
Posts: 7
Here's my issue....

Someone showed me a GRR study using JMP software. It printed out the following summary:

10.3334 % Gage R&R=100*(RR/TV)
0.16857 Precision/Tolerance Ratio=RR/(USL-LSL)

So the first one is comparing the percentage of measurement variance to process variance (as determined by the study data) while the second one is comparing the proportion of measurement error to the part tolerance.

Can you then say that the percentage of P/t is 16.857%?

Thanks a lot,
Rich DeRoeck
Supplier Quality Engineer/SPC Coordinator
Calibration Manager
  #7  
Old 13th October 2005, 02:08 PM
Miner's Avatar
Miner

 
 
Posts: 3,540
Quote:
In Reply to Parent Post by rderoeck

Someone showed me a GRR study using JMP software. It printed out the following summary:

10.3334 % Gage R&R=100*(RR/TV)
0.16857 Precision/Tolerance Ratio=RR/(USL-LSL)

So the first one is comparing the percentage of measurement variance to process variance (as determined by the study data) while the second one is comparing the proportion of measurement error to the part tolerance.

Can you then say that the percentage of P/t is 16.857%?
Yes. P/T = 16.857 %, which compares the gauge error to tolerance. This falls into the marginal are, but if it is not a critical dimension, it is probably acceptable.

The 10.3334% GRR % TV (Total variation) means the gauge is acceptable for performing process studies, such as DOE or capability studies.
  #8  
Old 4th December 2012, 01:42 AM
bryan3com

 
 
Posts: 1
Re: What does the P/t ratio (Precision/Tolerance) =RR/(USL-LSL) say about my gage stu

About P/T ratio there are two way to control it:
6sigma/USL-LSL*100% OR 3sigma/Tolerance

For the tolerance what kind of number should I put?
ppl told me to use "80% average" be the Tolerance. Is that correct?
Reply

Lower Navigation Bar
Go Back   The Elsmar Cove Forum > ISO (International Organization for Standardization) Standards > ISO 17025 - General Metrology, Measurement Device, Calibration and Test Laboratories > Gage R&R (GR&R) and MSA (Measurement Systems Analysis)

Do you find this discussion thread helpful and informational?


Bookmarks


Visitors Currently Viewing this Thread: 1 (0 Registered Visitors (Members) and 1 Unregistered Guest Visitors)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Forum Search
Display Modes Rate Thread Content
Rate Thread Content:

Forum Posting Settings
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Similar Discussion Threads
Discussion Thread Title Thread Starter Forum Replies Last Post or Poll Vote
Computing six sigma when the USL & LSL are varying patkim Six Sigma 16 8th June 2009 07:09 PM
Double-sided (USL, LSL) Variables sampling plan Z1.9 - Use in Excel spreadsheet? tdickson Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2 7th June 2009 11:08 AM
P/T (Precision/Tolerance) ratio for off-center processes? Process capability ratio? Strife Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3 24th June 2007 05:46 PM
Precision/Tolerance Ratio for 1-sided Specification - How to Compute argon - 2006 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3 9th October 2005 09:25 PM
Cp, Cpk calculation for np chart - No USL or LSL - SMT Production rikkyyee Capability, Accuracy and Stability - Processes, Machines, etc. 16 7th August 2002 10:36 AM



The time now is 05:35 AM. All times are GMT -4.
Your time zone can be changed in your UserCP --> Options.


   


Marc Timothy Smith - Elsmar.com
8466 LeSourdsville-West Chester Road, Olde West Chester, Ohio 45069-1929
513 341-6272
NOTE: This forum uses "cookies".