Sure Phillip, just put your Zone pill on the column shelf, then add a table calculation for the standard deviation and set the compute using to Table Across, although that may need to be Table Down depending on how you have your partitioning pills arranged.
Hope this helps!
Phillip, by "zones" are you referring to a point or series of points that have violated the Western Electric rules or are you talking about the zones on the chart itself: http://en.wikipedia.org/wiki/Western_Electric_rules#Zone_rules ?
It'd be helpful if you posted your workbook. I used this site to help in developing my control charts: http://dataremixed.com/2011/10/how-to-make-control-charts-with-tableau/ It will take some modification of the formulas he uses because in some cases their either wrong or use different rules (eg. 7 successive points to denote a trend rather than 6) but I'd be happy to help share what I've done.