# Quality control vs Quality Assurance.



## rickharris (Mar 6, 2009)

This is something I have a lot of trouble with getting the kids at school to grasp (either QA or QC).

My usual definition is: *Quality control* = measuring something. The most common situation is marking out your part and then double checking the measurements. What my Father used to call measure twice - cut once!

*Quality Assurance*= Some action or system to prevent making a mistake in the first place.

Example in marking out multiple parts make and check a template and then draw round it.

Or make/use a jig to guide the cut/assembly.

I guess in this hobby these are things that most do automatically (or make a lot of scrap) and yet in the general way of things people seem to find it hard to grasp.

Or I guess with much lower costs use CAD/CAM.


Thoughts anyone? is my definition wrong?


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## Kermit (Mar 6, 2009)

rickharris  said:
			
		

> Thoughts anyone? is my definition wrong?



Nope.  Your definition is pretty much accurate. The problem is 99.9% of people in the world don't, or can't differentiate between the two.  The two terms are used interchangeably for both of the purposes you stated.


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## Holescreek (Mar 6, 2009)

Defining QC/QA is similar to differentuating accuracy and precision. Despite dictionary and textbook applications they will be used interchangeably forever.


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## b.lindsey (Mar 6, 2009)

Very true, and these days further complicated by such terms as Total Quality Management, Statistical Process Control, and Six Sigma...to name a few

Bill


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## Maryak (Mar 6, 2009)

rickharris  said:
			
		

> This is something I have a lot of trouble with getting the kids at school to grasp (either QA or QC).
> 
> My usual definition is: *Quality control* = measuring something. The most common situation is marking out your part and then double checking the measurements. What my Father used to call measure twice - cut once!
> 
> ...



Rick,

At great personal risk, I beg to differ.  :

IMHO the template, jig, go/nogo gauge etc. are still part of the quality control process.

Quality Assurance is a form of guarantee that you/your company etc. will perform to a standard. The parts or service performed are being guaranteed as being in compliance with or exceeding whatever the standard criteria are, e.g. QA certified AS3009.

Oh I do hope the worms are still in the can. ;D

Best Regards
Bob


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## Jadecy (Mar 6, 2009)

regardless of the terminology you can't inspect quality into a product but you can gather information from an inspection to improve the process which which in turn will yield a better widget.

2 cents


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## rickharris (Mar 6, 2009)

Maryak  said:
			
		

> Rick,
> 
> At great personal risk, I beg to differ.  :
> 
> ...



As far as the proof that you have a quality system that is operating I agree. BUT doesn't the actual implementation of Quality Assurance on the shop floor involve taking actions that will be controllable and traceable.

For example using templates rather than asking the operative to measure - same as go - no go and use of CAD CAM. You have something that will be constant if use correctly and if something goes wrong (often caught in a random quality check) you can trace back and either correct the problem or improve/tighten the process/system

The external check that your company is doing all this consistently is, perhaps unfortunately, also often called Quality Assurance - and in a way it is.

An example - You will not know if some part meets its quality criteria unless all those criteria that affect the quality of that part are identified and quantified. 

That's fine and checks would be part of a QC regime. BUT the benefits of QA to you as a manufacturer who is trying to make many parts all the same is to have a system that ensures there will be no errors outside tolerance. 

After all if you find parts that are outside spec you are committed to reprocess or remake them - assuming you still want to end up with the correct end product.

I am just trying to tap the wide experience here to refine my understanding of this subject


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## Kermit (Mar 6, 2009)

Jadecy  said:
			
		

> regardless of the terminology you can't inspect quality into a product



You CAN inspect poor/no performance OUT of a product.

You are right that inspection cannot put anything INTO a product. It only removes the non-conforming specimens and increases the VALUE of the resulting "inspected" product by this process.

The ASSURANCE part is when you provide complete access to all the contractors and suppliers quality documentation as it pertains to the product you are making. A paper "trail" of all the who's and the where's, and evidence of functionality tests. EVERYTHING down to the littlest nut and bolt, complete with documentation that traces it as far back as the mother metals compostion testing and heat treatment(a requirement for parts in a US Rocket engine).

This doesn't put anything INTO the product that wasn't there to begin with. It only provides a higher level of "assurance" that your widget will perform as it is designed to. All thanks to the value added by practicing quality "control" in the manufacture of the widget.

I don't know Jack, but I've met his Mother, 8)
Kermit


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## Maryak (Mar 6, 2009)

Rick,
 Forgive me. ???

Let me try and give you an insight into my take on the difference using my role as a Surveyor.

When I issue a test certificate on an ISO tank, I am giving the client an assurance that the tank complies with the various standards outlined on its data plate.  Quality Assurance.

The test equipment, materials, tolerances, documentation etc. etc. are controls which give me the confidence or not to issue the certificate.  Quality control.

And on that note I will shut up. ;D

Best Regards
Bob


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## rickharris (Mar 7, 2009)

Maryak  said:
			
		

> Rick,
> Forgive me. ???
> 
> ...
> ...



I just reread my post from last night and I think I came over a bit hurt and didn't intend to do so. I am only too willing to listen and learn  so it is I who should say sorry.!



I can see what your saying bob and your view point. I think my view comes from the actual manufacturing angle - 

i.e. what can I do to make sure what I make is going to be OK - other than test everything to death - i.e  some kind of system to assure the quality.

I agree that end users want certification or some other review to say that the end product is good (at least when it was checked.)

I used to do QA for software systems which is a rather different product - can't see it, hear it, pick it up or often even truly measure it's performance so the only way to make even partially sure it will be correct is to have tight controls throughout the development process.

this is evidenced in the number of poor software products that get into big systems and then very publicly fail.


Thanks for your comments - I am still happy to discuss, only through that can we learn from each other.


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## Maryak (Mar 7, 2009)

rickharris  said:
			
		

> Thanks for your comments - I am still happy to discuss, only through that can we learn from each other.



Rick,

Thanks for the above and your understanding. :bow:

I see what you too are saying and I have come to the conclusion that we are down to semantics. You, (I think), are saying I want to be assured of the quality of my widget when manufacturing. I am saying I want to control the quality of my widget when manufacturing.  : :  

Interesting..... now we both know why the legal profession is such a can of worms.

Best Regards
Bob


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## kd7fhg (Mar 7, 2009)

Now my two cents worth!
Quality Assurance 
 A systematic review of Quality Maintenance records and all production actions which will provide adequate proof and confidence that work performed or material manufactured will perform as designed and that there is documentary evidence to this effect.

Quality Control 
 On the job supervision, management and inspection which identifies and ensures proper workmanship and/or materials are being produced.

I hope you all have a great day!
 KD7FHG


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## Maryak (Mar 7, 2009)

kd7fhg,

Sounds/reads good to me. :bow: :bow:

Best Regards
Bob


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## rake60 (Mar 9, 2009)

I've worked for a few different shops in my years.
The first one was a production shop where QA and QC were considered the same.
It was a process of the machine operators sorting the bad parts out of the production run.

Now QA comes first. It is making certain the machines are capable of doing the job, the
proper tooling is available, the print is accurate and the machine operators are properly
trained to run the machines.

From that point it is QC. If the machinist makes an error and decides to let it go anyway
it's probably time to find him something to do other than operating a machine. Even the most
conscientious could make an error that they do not catch. The inspection department better
catch it!

That is what I like about my home shop.
If it fits it's perfect.
If it doesn't fit but be can fixed to, it's still perfect.
If it can't be fixed call it a practice piece and make another one. 

Rick


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