Re: First Time Completing a 5 Why/RootCause
Well, I'll throw in a couple of cents...
I'm not sure I followed your approach. The 5-whys (and 5 is just a number, not a mandatory count) are intended to help you drive to the root causes (and do note there can be more than 1). So the last sentence in your 'Root Cause' statement is probably close to *a* root cause, but I would ask why isn't there 100% inspection to detect undersized parts?
It looks like you did the work in isolation. You need the stakeholders involved. Your recommendations may be fine but without stakeholder agreement, they're likely to not be implemented.
I would sit down with the manufacturing folks and go back through the process.
Ask them their view on why 1 in 50 were short. Take the questioning from there (continue asking why - without sounding like a 2-year-old!) to try to isolate root causes (and remember there may be more than 1 so you may have to 'branch' the questioning).
Bear in mind that the 5-why method is just one technique at finding root cause. Other methods like fault tree analysis may be better suited to the problem.
For your containment, why was it limited to just that one lot? Note that if other product is run on that same equipment, there may be issues there as well! So consider other lots and other products.
Finally, how will you know if your changes have the desired effect (and don't have any negative effects)? You need a plan on how to verify this and a plan on how to determine effectiveness.
You're to be commended for giving it a good run. You shouldn't have to do it in a vacuum, though! It needs to be a team exercise to ensure that you have identified the problem, put the right fixes in place, and ensure it's all good.