posted 18 February 2000 03:19 AM               

As a normal rule you cannot make a capability study unless you have already demonstrated the stability of your process, and you need at least 30 data if you use average lectures and more than 100 for individual moving range charts.
However,(I declare : I am not an expert in this field) you can run some short time period (or preliminary)studies to have an idea of your process capability using let us say.. 7 lectures, but in this case you must close your gap and instead of using 3 sigma you have to use 4, I think to "compensate" of using few points.

What other folks think ?

posted 27 February 2000 07:11 PM               

That said, in this instance, based on the description of the product there are few parts made per day, them how about just adding the new data onto the old in a run chart of some sort. I assume that there was historical data that suggested the need for improvement, so take some "after" parts (seperate enough from the "before" parts - maybe a "purge" of the process) and add the sample data to a run chart of the prior data - Average and moving range, for example. If the large size is an indication of being able to run only a few per hour or day, then I think only a few could be necessary. The improvement (or lack thereof) should be obvious. IF there is an improvement, continue to run more parts, enough to see expected variation over some time, then calculate capability.