Capability study on true position callout. What would be the upper and lower spec?

E

eypon

#1
Hello all,

I have a question my customer is asking me to do a capability study on a True position call-out of 2.0mm in diameter. What would I input as the Upper and Lower Spec Limits?

Thanks

Eypon
 
Elsmar Forum Sponsor
J

jrubio

#2
If the Customer does not set tolerances in the Customer Drawing, just establish you as Supplier the tolerances:

i.e: Dmax, Dmin. meassuring some parts you have.
 
Last edited by a moderator:
J

jrubio

#4
In fact there are 3 grades of fredom.

The center coordenates:
X, Xmax, Xmin.
Y Ymax, Ymin.

D , Dmax, Dmin

That´s why many companies use this charasterist as Attributive and therefore to compare with a master. (If attributive var no capability is feasible according with the manual)

If you have to meassure a Capability for that var you have to meassure 3 vars.

¿Do this charasterist define your process, segurity, significant?.

No, Use other. more easier to meassure
 

Jim Wynne

Staff member
Admin
#5
Hi Eypon

If the true postion tolerence itself is 2mm
it becomes max spec
zero is your lower spec

Prabhu
It depends on the software, I think. In some instances, there is a difference between making no entry and entering a zero. The latter might cause errors. Most software has can explicitly handle unilateral tolerances, though. There's a good description of process capability formulae, including those for unilateral tolerances, here
 
T

Trae1170

#6
Re: Capability study on true position callout. What would be the upper and lower spe

True Position as is all form tolerances are 99.9 % of the time unilateral, so you would only have a upper limit. The only time that I can think of where they may be a bi-lateral tolerance would be for callouts like .00002" - .0001" Flatness, I measure parts with this tolerance and it is bi-lateral. There are probably others but they are not the norm.

Like previoiusly stated, make sure the software or excel form you are using will calculate unilateral tolerances and you enter this information correctly (either enter a zero or leave the lower tolerance blank; on the form I use, you actually have to specify if it is a bilateral or unilateral tolerance and if you indicate unilateral it automatically blanks out the box for the lower limit). What type of gage are you using to check position, a fixture (attribute gage) or something like a CMM (variable gage)? In the positional dimensions that I inspect, I use a CMM. I am able to either enter the calculated position or I can use the X,Y & Z coordinate values it reports. The coordinate values are much more accurate, they tell the exact location, whereas the calculated positional value basically tells you what zone you are in, but because your zone is a circle you do not know exactly where you are at (EXAMPLE: .0002" position could be .0002" anywhere within that zone, whereas X=2.00 , Y= -.999 & Z=1.250 is an exact location.)

Thanks,
 

Mezzaluna

Registered Visitor
#7
Re: Capability study on true position callout. What would be the upper and lower spe

it also depends how the tolerance is written. Is it a diametrical (Ø) true position tolerance? If so your the upper limit will be the old "two times the square root of a squared plus b squared" - unless I;m reading the question wrong that is. If so , apologies.

Mezz.
 
T

tenaiwa

#8
Re: Capability study on true position callout. What would be the upper and lower spe

Hello,

Here we need to use 3 different laws. Normal law, Form defect law also known as folded Normal law and finally Rayleigh law:

a. Normal law:
this law can be used only for double limit characteristic, which mean characteristic which has a defined minimum and a defined maximum. For example: we can not use it for shape defect characteristics because they have only a maximum. The better we are the more our results will tend to 0, but also the more our Cpk will tend to 0, which would mean that our result is really bad...

To sum up: use Normal law only for dimensional characteristics (example: 55 +0.1/-0,05 or 61 +0,2 -> 61 +0,2/-0)

b. Form Defect / Folded Normal Law:

This is one variant of normal law.

for quick explaination:
for unilimit (maximum) characteristics.
when raw results of the measurement machine can be negative and are always positive after calculation.
Raw result are according normal distribution. When calculating the absolute value we some how fold the result on 0 axis.

for detailed information, please, look in internet: folded normal distribution

To sum up: use it for positioning and some of form defect characteristics (see enclosed file)

c. Rayleigh Law:

for unilimit (maximum) characteristics.
When even raw results can absolutely not be negative (Cylindric positioning, concentricity...).

for detailed information, please, look in internet: Rayleigh distribution
 
Thread starter Similar threads Forum Replies Date
Q Capability study with a minimum spec Statistical Analysis Tools, Techniques and SPC 8
S Capability or Gage R&R Study for Leak Tester? Reliability Analysis - Predictions, Testing and Standards 15
S Machine Setup for a CNC Machine Capability Study Capability, Accuracy and Stability - Processes, Machines, etc. 1
G Capability Study for Tapped Hole Reliability Analysis - Predictions, Testing and Standards 3
G Plotting capability study data - I have a bimodular data distribution Capability, Accuracy and Stability - Processes, Machines, etc. 4
V Generic requirements regarding capability study in automotive Capability, Accuracy and Stability - Processes, Machines, etc. 1
O Capability or Gage R&R Study for Leak Tester Reliability Analysis - Predictions, Testing and Standards 11
M IATF 16949 - Capability study on non critical dimensions? Statistical Analysis Tools, Techniques and SPC 4
L Excel Template for Cgk Study wanted (Capability Gauges Study) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 12
ncwalker Process Capability Study - Aggregate vs. Individual Processes Statistical Analysis Tools, Techniques and SPC 24
KyloDen Capability Study and Qualifying a Supplier Capability, Accuracy and Stability - Processes, Machines, etc. 5
B Capability Study => Check %Study Variance and NDC? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
B Conflict between department of MSA and Capability Study Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
J How to determine a Capability Study for Low-Volume Suppliers Capability, Accuracy and Stability - Processes, Machines, etc. 3
S What is Cc? Capability Study on Key Critical Dimensions Capability, Accuracy and Stability - Processes, Machines, etc. 9
L Capability Study for a Honing Machine Statistical Analysis Tools, Techniques and SPC 3
A Inspection Capability Study (Kappa Analysis / Attribute R&R) as Certification Req't Training - Internal, External, Online and Distance Learning 7
C Subgroup Size in Minitab for Capability Study Statistical Analysis Tools, Techniques and SPC 4
O One Cavity Mold Prototype Capability Study and PPAP Approval APQP and PPAP 1
G How to calculate Subgroup Size for Machine Capability Study Statistical Analysis Tools, Techniques and SPC 4
V How to calculate Machine Capability Study using Minitab Using Minitab Software 4
V JCI standard numbers of pieces required for Capability Study? APQP and PPAP 2
T Industry Standards for # of parts for Capability Study and Layout FAI's? APQP and PPAP 4
D AIAG 4th Edition Capability Study and Gage R&R Requirements Document Control Systems, Procedures, Forms and Templates 8
P Capability Study for a Specific Thickness of Rubber Sheeting Capability, Accuracy and Stability - Processes, Machines, etc. 6
Q When to use Cpk or Ppk for a Process Capability Study? Capability, Accuracy and Stability - Processes, Machines, etc. 14
O Capability Study on Continual Arbitrary Dimension Capability, Accuracy and Stability - Processes, Machines, etc. 11
J Attribute Data and Capability Study of Holes in Parts Capability, Accuracy and Stability - Processes, Machines, etc. 11
D Process Capability Study which involves MMC (Maximum Material Condition) Capability, Accuracy and Stability - Processes, Machines, etc. 8
A Yearly MSA (Measurement System Analysis) & Capability Study - TS 16949 Requirements Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
J Process Capability - Interview Case Study Capability, Accuracy and Stability - Processes, Machines, etc. 1
A Process Capability Study using Variables Data (weight of the product) Statistical Analysis Tools, Techniques and SPC 9
M Capability Study on a New Machining Process - Issues Capability, Accuracy and Stability - Processes, Machines, etc. 40
S Does anyone know what is involved in a HiPot capability study? Capability, Accuracy and Stability - Processes, Machines, etc. 2
A Process Capability study of CNC Machining Process Capability, Accuracy and Stability - Processes, Machines, etc. 3
Q Machine Capability Study - Cpk (Cmk) of an R/F testing machine Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
B MSA (Gage R&R) vs. Capability Cpk Study - Helium Leak Check Station Statistical Analysis Tools, Techniques and SPC 2
T Machine GR&R (Gage R&R) - Capability Study Capability, Accuracy and Stability - Processes, Machines, etc. 5
M Cmk (Machine Capability) - Case study Capability, Accuracy and Stability - Processes, Machines, etc. 5
Barahir Visual Inspection - Capability Study on Attribute Data Capability, Accuracy and Stability - Processes, Machines, etc. 13
M Capability Study on Extruded Alumin(i)um - How would one define a "batch"? Capability, Accuracy and Stability - Processes, Machines, etc. 4
A Capability Study Template Capability, Accuracy and Stability - Processes, Machines, etc. 1
C Capability Study Required as a Condition to Adopt a Sampling Plan? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 6
sridharafep Process Capability Study for Electrostatic Powder Coating Statistical Analysis Tools, Techniques and SPC 6
J Process Capability Sheet for a short term 30 piece study needed Statistical Analysis Tools, Techniques and SPC 1
B Capability Study for Radii of laser cut pockets - 0.030" radius Capability, Accuracy and Stability - Processes, Machines, etc. 15
V Machine short term capability study with Cmk index in automotive industry Capability, Accuracy and Stability - Processes, Machines, etc. 3
A How do you identify your heat treat capability study samples? Capability, Accuracy and Stability - Processes, Machines, etc. 3
K Format for presenting capability study results? Statistical Analysis Tools, Techniques and SPC 7
Manix Initial Capability study on N50 parts - Subgroup Size? Statistical Analysis Tools, Techniques and SPC 5

Similar threads

Top Bottom