Establishing Thickness Specifications from Measured Data

P

piningg

#1
Hi. I have some thickness data and I want to suggest a thickness specifications into our team using these data..any formula

Thickness ( millimetres)3.273.383.473.713.693.693.763.793.913.693.743.663.213.353.493.463.463.453.523.443.343.373.443.29mean3.52stdev0.184min3.21max3.91median3.465
 
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Jim Wynne

Staff member
Admin
#2
Re: newbie here need help

Hi. I have some thickness data and I want to suggest a thickness specifications into our team using these data..any formula

Thickness3.273.383.473.713.693.693.763.793.913.693.743.663.213.353.493.463.463.453.523.443.343.373.443.29mean3.52stdev0.184min3.21max3.91median3.465
Two things: if you could separate the numbers, perhaps by listing them in a column, it would make things easier. The way it is, it's impossible to tell where one number ends and the next begins. The other thing is that you also need to consider the application--what will work and what won't--in determining a tolerance range.
 

Wes Bucey

Quite Involved in Discussions
#3
Re: newbie here need help

Hi. I have some thickness data and I want to suggest a thickness specifications into our team using these data..any formula

Thickness3.273.383.473.713.693.693.763.793.913.693.743.663.213.353.493.463.463.453.523.443.343.373.443.29mean3.52stdev0.184min3.21max3.91median3.465
I have a hunch you tried to clip and paste a table - the formatting doesn't transfer. Better to convert the table to text in your native software, separated by some delimiter like coma, semicolon, or paragraph, and then clip and paste the text into your post.

As it stands, I would only be guessing - it might help in visualizing if you were to include the unit of measure and the likely instrument folks would use for confirming and validating the specification.

Typically, the horse comes BEFORE the cart and engineers specify the thickness to fit the function. Reverse engineering derives working specifications from a group of samples, but even then, the original process is known in order to separate natural variation of the process from desired tolerances.
 

BradM

Staff member
Admin
#4
Re: newbie here need help

I'm speaking out of school, here, so please correct what I incorrectly state.:whip::tg:

Would you not be setting capability limits by analyzing the data? I would think (like Wes mentioned) tolerance limits would come from the customer or something. Or... could you take the average, and set like values out from it, like Steve does with control charts? Since he uses Chebychev, Chevchev,... that inequality, you would not have to assume normality.
 
P

piningg

#6
Re: Establish thickness specifications from measured data

actual its a developmental stage of our product. The datum attached are thicknesses in mm measured by a dial gauge.
I want to suggest a thickness tolerance ( internal ) base from the machine capability. Hope Im clear as a mud.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#7
Generally speaking, I look to +/-4 std dev as specification, as it will yield capable process. HOWEVER, you may have to target +/-5 or 6 if you have not accommodated significant lot to lot variation with your data (data derived from one lot of a material with known significant variation between lots). That would require more knowledge of the process inputs. :cool:
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#9
several questions: what is this data? is it in process data or is it final product data?

what structure was used to generate the data? Bob is correct in that your process perfromance will be affected by set up to set up variation, raw material variation, tooling or other consumable variation, operator variation, time of day, cold equipment hot equipment, etc. Without understandign the process and it's components of variation, we cannot be sure if you have captured the full range of variation one can expect under normal conditions (without process improvements)

As for specifications - They alwasy come from the customer. even in process or input factor tolerances as these all compbine to create teh final product tolerances which must meet custoemr needs. (Now of course teh customer doesn't always tell us directly what they want.)

Bob - please clarify for everyone what you mean by "process specifications" and how are they different from product specifications
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#10
Bob - please clarify for everyone what you mean by "process specifications" and how are they different from product specifications
No problem. Let's say you have a print of a finished product. All of those dimensions, etc., are product specifications.

As an example, one of the dimensions is a spline. Before making the spline, you turn the base part to a diameter. This diameter is not on the product print, but you need to control it to get proper fill and pressure on your spline broach tool. The specification for that diameter is a process specification.

If you feel you need to hold a product dimension tighter to allow your processes to work better, the tighter dimension on your process print (not the customer print) is a process specification.
Hope these examples help...:cool:
 
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