Stacking a tiered cake can be intimidating stuff. This 4 step process helps break it down and makes it a little less scary.
You will need:
1) Trace Circle : On top of your bottom layer, center a round cardboard that is the same diameter as the layer you are stacking on top of it. Use a ruler to make sure there is the same amount of space all the way around and that the cardboard is centered. Trace the cardboard with a toothpick.
2) Insert Straws: Within the traced circle, insert a straw and use scissors to snip the straw flat to 1/8" above the surface. Continue doing this with additional straws, taking care to place them evenly across from one another. (Note: Our general rule for the number of straws used is the same number as the diameter layer you are trying to support. For example, if you are placing a 6" layer on top, peg the area with 6 straws.)
3) Add Top Layer: Within the pegged circle, pipe a few dollops of buttercream to act like glue. Use a spatula to lift and place your next tier. Use a ruler again to measure the amount of remaingn space to confirm the layer is centered. Reposition if necessary.
4) Center Dowel: (This step is optional but is highly recommended if traveling with a tiered cake). Sharpen one end of a wooden dowel using a craft knife or a pencil sharpener. Hold the dowel in front of your stacked cake and make sure the dowel measures 1" shorter than the total height of the cake. If not, trim with woodclippers. Place the dowel in the center of the top tier and drive through the cake by pounding with a hammer, until just above the surface of the cake. Place a second dowel on top of the first and pound the second, driving the first into the cake and into the support board.Set aside the second dowel and fill the remaining hole with buttercream.