Mark tier for hidden pillar placement. Use the separator plate for the next tier above, gently pressing it into the cake tier, feet down, making sure it is centered. Lift plate away. The feet will leave marks on the icing to guide the position of pillars when you assemble the tier. Repeat the process for each tier, working from the largest to smallest tier. The top tier is left unmarked.
Insert pillar into cake straight down to the cake board. Mark pillar the exact height of cake tier. Pull pillar out.
Trim pillars at marking with serrated edge knife or pvc cutter.
Insert pillars in cake.
Position tier above on pillars.