Xbar-mR-R (Between/Within) Control Chart

When using an Xbar-R chart, the short-term variation is given by the within-subgroup variation on the range chart. The long-term variation is given by the between subgroup variation on the X chart. But what happens when the process is such that it is not possible for the short-term variation to be consistent with the long-term variation?
In this video we look at how to address this situation. We start with a brief review of Xbar-R charts. We then look at what the Xbar-R control charts often looks like when you have situation where there is a significant difference between the within-subgroup variation and the between-subgroup variation. You will see that the control limits on the Xbar chart are very tight and most of the points on that chart are beyond the control limits. We finally look at how to handle this type of situations by using three control charts.
Quickly make your own Xbar-mR-R Control Charts by downloading the free demo:
www.spcforexcel.com/spc-softw...
Keep learning about SPC from our 220+ acclaimed Knowledge Base articles: www.spcforexcel.com/spc-knowl...
Support our Channel - Subscribe and Comment😊

[@domenicoscarpino3715]

Great lesson. I have a question. You said in the video "when you have enough points you calculate the overall averages and the control limits". What happens when we don't have enough points and how many points do we need to be enough? Thanks in advance

[@SPCforExcel]

Thank you for your comments! Check out this article from our SPC Knowledge Base. You will find lots of good details about your questions here: www.spcforexcel.com/knowledge/control-chart-basics/how-much-data-do-i-need-calculate-control-limits/

[@domenicoscarpino3715]

​@@SPCforExcel thank you, I'd also really appreciate if you can suggest an article that talks about when to use the Xbar-mR-R chart. I understand what it does, but I would like to look further into some pratical cases where this happens to be the right choice. I suppose when we don't want to consider batch to batch, operator common cause variability...

[@SPCforExcel]

This article may be a good one for you: www.spcforexcel.com/knowledge/variable-control-charts/comparing-x-mr-and-xbar-r-charts/

[@domenicoscarpino3715]

@@SPCforExcel thank you very much