I have only made a 2 tier cake. When I place the 2nd tier on, I have a cake board under the 2nd tier and I place it on the dowels of the 1st tier.
Now I would like to make a 3 tier cake. Do you put a dowel through all the tiers, and if you do, what happens to the cake board under each tier?

Each tier must sit on a cake board.

Ther must be dowels in the bottom tier to suppor the middle tier and in the middle tier to suppor the top tier.

A center dowel is only neccessary if you will be transporting the cake assembled.

To insert the center dowel, sharpen it using a (new) pencil sharpener, then gently tap it through using a rubber mallet. The sharpened point will go through the cake boards and lodge in the cake drum.

HTH!