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.
 

ncwalker

Trusted Information Resource
#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
Darius t2 Hotelling or Chi square Control Charts - How is done - Calculus and charting? Statistical Analysis Tools, Techniques and SPC 2
I Control Plan (Product/Process specification/ Tolerance) acceptance FMEA and Control Plans 27
Sravan Manchikanti How to interpret '8.3 Control of nonconforming product' for SaMD device while implementing ISO 13485 & MDSAP ISO 13485:2016 - Medical Device Quality Management Systems 4
Z Putting back excluded rows/data points in a control chart Using Minitab Software 0
J Control Plan use on the manufacturing floor FMEA and Control Plans 4
E Change in control plan - Do I have to do sampling? IATF 16949 - Automotive Quality Systems Standard 1
D All Dimensions listed on control plan FMEA and Control Plans 10
W Need for current design or process control FMEA and Control Plans 2
Q ISO 9001 8.5.1 - Control of production and service performance ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
A What is the difference between Design Process, Process Design and Design Control? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 2
A Beginners help with ISO3951-2 Combined control s-method n>5 what is Phi ?? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
C Corrective action for failure in documents control ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 10
B Control chart and sample time Statistical Analysis Tools, Techniques and SPC 1
DuncanGibbons Manufacturing Plan vs Material Specification vs Control Plan Manufacturing and Related Processes 4
J Control chart for huge sample size Statistical Analysis Tools, Techniques and SPC 9
K Contamination Control - Class Is medical devices (Clause 6.4.2 ISO 13485:2016 (E)) ISO 13485:2016 - Medical Device Quality Management Systems 12
J 510(k) for a control kit for an external IVD test kit 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 1
T Assessing Hazard-Related Use Scenarios where control measures exist through standards IEC 62366 - Medical Device Usability Engineering 25
adir88 Documenting Risk Control Option Analysis ISO 14971 - Medical Device Risk Management 8
T Design Control Procedures later in the Development Process ISO 13485:2016 - Medical Device Quality Management Systems 6
L AS5553 Clause 3.1.7 e "Control packaging material ..................reused" AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 0
T Attributes SPC study - Attributive control (Go gage) Statistical Analysis Tools, Techniques and SPC 5
K Process Mapping - Inputs/Outputs/Detail Activities/Control points/Measurement? Process Maps, Process Mapping and Turtle Diagrams 4
S Should safety checks be included in the Control Plan? IATF 16949 - Automotive Quality Systems Standard 5
D Infrastructure: Equipment, Work Environment and Contamination Control ISO 13485:2016 - Medical Device Quality Management Systems 4
Q Relabeler for patent expired product - design control responsibilities? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 2
J How to make Quality Control plans Quality Tools, Improvement and Analysis 5
I Document Control on Log Files ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
Q Tracking Procedure Revisions (Document Control) Document Control Systems, Procedures, Forms and Templates 9
C Document Control Stamps - Does anyone still stamp their documents? Document Control Systems, Procedures, Forms and Templates 24
D Supplied Product on Control Plan - Lot ranging in 40,000 pcs per product FMEA and Control Plans 3
D IEC 62304 Risk Classification - With and without hardware control IEC 62304 - Medical Device Software Life Cycle Processes 2
J Antiviral Mask or Mask to Mitigate or Control Corona Virus Manufacturing and Related Processes 30
A UDI and Design Controls - Labeling change via the Design Control process 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 1
I Control of Documentation Distribution - Document Control ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
S Inventory Control - Any thoughts would be appreciated ISO 13485:2016 - Medical Device Quality Management Systems 2
H SPC for special characteristics - CSR - Control of SC and CC Statistical Analysis Tools, Techniques and SPC 1
T Control of downloaded document copies by employees Document Control Systems, Procedures, Forms and Templates 3
T Document control ISO 13485:2016 ISO 13485:2016 - Medical Device Quality Management Systems 5
M Is there any pre-defined Control plan format/template acc. VDA? VDA Standards - Germany's Automotive Standards 0
B Record Management - Does the QMS need to control templates of records? Records and Data - Quality, Legal and Other Evidence 17

Similar threads

Top Bottom