Non math approach to SPC
JSW05 said:
Lately I find myself spending a lot of time explaining the basic "rules" of control chart evaluation to suppliers and coworkers. I put together the attachment to use as a basic explanation and reference, mostly so I could stop having to repeat the same explanation over and over again. I wanted something reasonably concise--a single page--and wasn't attempting a treatise. I'd like to have my fellow Covers look it over and offer suggestions for improvement, and also offer the reference to anyone who might find it useful.Thanks, Tim
I like it a lot.
One thing I have now done here is to use only real examples from our own shop. We now have lots of examples. I started with the examples fropm textbooks, buy now use only our charts.
We only have 3 rules in play (points out of control, sudden shifts, and mixture), so that's all I explain.
I also teach people to look at the range chart first....only because most people ignore it.
I also don't talk in terms of probability and the normal curve...instead I give everyone 2 dice and have people roll them and shout out the numbers. I record the results in a Pareto and after about 80 throws, or less than 1 minute I have a nice bell shaped curve.
This 2 dice machine makes numbers...from 2 to 12...it mostly makes 7's....if it makes a 1 it is broken...and my favorite (per Deming) the operator is not to blame or in control....I usually tell people that I will bankroll anyone at the Casino if they can control the outcome of this machine!
Then I say the control limits are set "near" the ends of the curve and act as your signal to look at your machine, because you have an unexpected result....everyone gets this and nods their head...then I offer my time to go through the math if anyone wants it.....a few people do take me up.
People also get the idea of a run easily....if someone start rolling all 7's....you need to shoot them....they're cheating!
So there's my no math approach to it all. Don't get me wrong, I love the math! But no one needs any math to get SPC.
Also as per Shewart, Wheeler, and Prevette, normality is not required for SPC! (I know, I know, it is required for prediction and capability.)