SBS - The Best Value in QMS software

Control Charting a Feature with Bonus Tolerance

U

useridpain

#1
Does it make sense to use an X Bar and R Chart to chart a feature with bonus tolerance? Would there even be a LCL? I just came off the shop floor and seen where they are using and X Bar & R chart for a true position with a maximum material condition call out and there are upper and lower control limits. Isn't that like trying to aim for a moving target?:confused:
 
Elsmar Forum Sponsor

howste

Thaumaturge
Super Moderator
#2
Re: Charting a feature with bonus tolerance

Welcome to The Cove, useridpain! :bigwave:

Since there is no relationship between control limits and specification limits, I don't see a problem. The control charts are looking at the process variation without regard to the specification.
 
N

ncwalker

#3
Re: Charting a feature with bonus tolerance

Howste is correct.

Sometimes, however, people DO want to see data to a specification. And you are correct, MMC is then a moving target. The answer is to scale it. Call full tolerance (whatever it may be based on the diameter) a "1". Then if they are halfway to this one, you plot at 0.5. Three quarters of the way, you plot 0.75

Datum modifier bonuses make the statistics harder. (They make TOTAL sense when you consider you may be getting mating components from two different sources). Don't get me started on true position and capability ....
 

Miner

Forum Moderator
Staff member
Admin
#5
What type of GDT dimension are you trying to chart? The complicating factor is not the bonus tolerance, which as noted earlier, is irrelevant in SPC. The problem is that GDT dimensions are typically absolute values, and some are partial polar coordinates.

If you are trying to do SPC on Position, you would be better off using the X/Y coordinates than the polar coordinates. Others such as flatness or parallelism are absolute values and may be highly skewed the closer you get to zero (see folded Normal distribution). This can cause nonsensical negative LCLs and more false alarms above the UCL.
 

Miner

Forum Moderator
Staff member
Admin
#7
It is a true position of a hole, .003, at maximum.
I would use SPC on the x and y axes. If the position was out of control on position, it could be out in any direction around 360 degrees. You would have to look at the x and y coordinates to discover where the problem lies.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#9
what Miner said!

SPC should tell you what the process is doing. and to do this we need to use the raw data as the process creates it. bonus tolerances and other manipulations take us away from visualizing the process...

the old adage to keep it simple will almost never fail you. The point of SPC is so the operators know what is happening so they properly adjust things.


the issue with trying to do SPC and Spec limits is like using a spork. it really isn't very good at either...
 
Last edited:
Thread starter Similar threads Forum Replies Date
A Process Control / Control Charting Procedure Capability, Accuracy and Stability - Processes, Machines, etc. 1
Q Real Time Electronic SPC/Control Charting Statistical Analysis Tools, Techniques and SPC 4
S Different Standard Deviations used in Control Charting Statistical Analysis Tools, Techniques and SPC 8
Hami812 Minitab and Control Charting Time to Complete each Repair Over Time Using Minitab Software 8
Hami812 Collecting Data for SPC Control Charting Statistical Analysis Tools, Techniques and SPC 7
R Control Chart Metrics/KPI - Measuring Effectiveness of Control Charting System Statistical Analysis Tools, Techniques and SPC 4
P Can we use Control Charting to monitor Rejection Rate? Statistical Analysis Tools, Techniques and SPC 3
N Which is more appropriate Regular or Short Run control charting? Statistical Analysis Tools, Techniques and SPC 8
J Continuous Gauge Control Charting Statistical Analysis Tools, Techniques and SPC 1
D t2 Hotelling or Chi square Control Charts - How is done - Calculus and charting? Statistical Analysis Tools, Techniques and SPC 2
D Use Error Risk Controls and Control Verification ISO 14971 - Medical Device Risk Management 5
S Maintenence related action in Control plan FMEA and Control Plans 3
M ISO 13485 and document control for programs ISO 13485:2016 - Medical Device Quality Management Systems 6
R Control Methods in Control Plan FMEA and Control Plans 4
M Design Control - Management of Electronic CAD files Design and Development of Products and Processes 11
S TSCA (Toxic Substances Control Act) PIP 3:1 RoHS, REACH, ELV, IMDS and Restricted Substances 0
S Use of Attributes Control Charts Statistical Analysis Tools, Techniques and SPC 1
U Appraiser Out of Control Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
L Looking for Control Plan and FMEA Stamping process FMEA and Control Plans 2
Z AS9100 Control of Nonconforming Outputs - Rework Dispositions AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 8
K ASME, ANSI, ASTM and similar specifications and their requirements for document control. Inspection, Prints (Drawings), Testing, Sampling and Related Topics 8
Z Software for design control ISO 13485:2016 - Medical Device Quality Management Systems 5
K Quality Control/Assurance in the Metal Industry Quality Tools, Improvement and Analysis 10
K Defining risk control measures IEC 62304 - Medical Device Software Life Cycle Processes 14
J Warehouse temperature and humidity control EU Medical Device Regulations 7
Jimmy123 IATF16949 Control Plan FMEA and Control Plans 1
D Control Number for Class III and IV devices Canada Medical Device Regulations 1
J Document Control Metrics Document Control Systems, Procedures, Forms and Templates 3
I Document Control Software Document Control Systems, Procedures, Forms and Templates 2
T Controlling Expandable Forms in Paper-Based Document Control System Document Control Systems, Procedures, Forms and Templates 10
N ISO 13485 7.3.9 Change control in medical device software ISO 13485:2016 - Medical Device Quality Management Systems 6
C UDI Questions on Control Units Other US Medical Device Regulations 6
A Quality Control Datasheets Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
M Control-self assessment Internal Auditing 5
GreatNate Master Control QMS software Quality Tools, Improvement and Analysis 1
A Prototype control plan FMEA and Control Plans 2
J Records Control - Does each individual record need to be numbered? Records and Data - Quality, Legal and Other Evidence 2
shimonv Document Control Procedure Header Content Document Control Systems, Procedures, Forms and Templates 4
W FMEA - Current control and occurrence rating FMEA and Control Plans 3
S Which department should prepare the control plan? could you show me a standard regarding to this matter. FMEA and Control Plans 17
G Control Plan & PFMEA Review Procedure? FMEA and Control Plans 8
N What are the software audit and control steps Reliability Analysis - Predictions, Testing and Standards 2
A Fabric roll inspection - What type of Control Chart to use? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
C Monitoring and Control Instruments RoHS, REACH, ELV, IMDS and Restricted Substances 3
M ISO14971:2019 - Verification of implementation and effectiveness of risk control ISO 14971 - Medical Device Risk Management 3
T Risks arising from control measures vs. ineffective control measures ISO 14971 - Medical Device Risk Management 11
J Need Change Control Yes/No Decision Tree Template ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 1
P IQ, OQ, PQ protocol, and report templates for Distributed Control Systems in Pharmaceutical Manufacturing Systems. Qualification and Validation (including 21 CFR Part 11) 0
R Risk control measures as per ISO 14971 ISO 14971 - Medical Device Risk Management 6
T Linking Control Plans and PFMEA's FMEA and Control Plans 3

Similar threads

Top Bottom