Haw many plastic dowel rods do I need to support a 10", 8" and 6" cake in stacked construction? I've never used them before and I 'm not sure exactly how many to use in each layer (10' and 8" are the only ones that need them I know, but how many??)

http://www.cakecentral.com/article49-Building-The-Cake-Combination-Pillar--Stacked-Construction.html