I'm attempting to make this cake for my daughter's birthday and need advice about how to structurally set it up? Do I need to use plywood bases and screw the dowels from the bottom tier to the top tier? Or are there any other ways to do it?
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I don't think you need to use plywood. I would use something like SPS or the Wilton plate that the pillars attach to, and don't transport it already stacked.
Do I need to use plywood bases and screw the dowels from the bottom tier to the top tier?
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I'd do exactly what you mentioned, but without the plywood. The carousel canopy top tier isn't so huge to require plywood, but you could do the same thing with a cake drum. If I'm understanding you correctly, you'd put screws through the top tier's baseboard or drum into the top of each dowel to secure it just like a table with legs, then push the entire assembly into the bottom tier just as you would with the SPS system.
Or you could make the top part from styrofoam and not have to worry about needing a lot of support at all . If you do that, the poles can be just covered wooden dowels. You can always make the bottom cake larger or two tiered if you need more servings.