This has probably been asked before:
When you cut dowels/straws to brace cakes for stacking, should the cut be made to match the height of the cake, or the cake with icing. This seems like a very rudimentary question, but I want to make sure that I do it right.
Also, how many do you place? For instance, if you are stacking a 6" round centered on a 10" round how many would you put?
Well, since you dowel cakes after they're iced, the dowels are cut to the height of the iced cake because you can't see exactly how high the cake below the icing is and everyone applies different thicknesses of icing anyway.
Peg and stack like this:
(don't overdowel because you'll perforate the cake to fall apart along the "dotted" lines.)
Sharon Lambito has a fantastic DVD called Successful Stacking. If your library carries it, definitely worth watching!
I think the general rule is one dowel every 2 inches....but what I generally did (thinking from a clock)was one at '12', '3', '6', and '9' postion around the perimeter, then one or more in between as warrented by the size of the cake. I also generally put in 4 more towards the center.
For 6" cakes, I usually only put in 4 dowels.