I am going to "attempt" to make a 3-D motorcycle cake today and need some advice from the carving experts. The instructions call for a 1/2 sheet divided into 1/3's and stacked. This will make the uncarved cake about 6X12X6" high. I'm wondering if I need to dowel and cardboard the top layer for support?? My issue is when I go to carve it, won't the board get in the way?? Or should I cut the board much smaller than the top layer to make up for that?

Here is a picture of the cake.

Three million dollar question. I think I would carve the cake and then cut the board by laying your carved layer and tracing around, in order to get correct size. You can precut it smaller than you think the cake will be, but if it ends up not being the right size, you have to either cut it while stacked with exacto or take apart and cut it that way. I ran into this problem with the Colette Peters cake (in my photos), that I had to do for a wedding. I cut the board first smaller than I thought the cake would be and ending up having to carve more cake than I thought, it was a hassle. I am sure some one else on here will have better advice, there is a definite learning curve there.

Good idea! The more I look at the picture, the bigger the knot in my stomach! I hope I can get it to look something like a bike!

I am making a train cake this weekend and each car will measure 15" long x 3" wide x 5 inches tall. I will do a limited amount of carving but Doug on CC told me I wouldn't need to dowel or put an extra board in because I'm covering it in fondant. He said to just make sure the bottom cake board is securly anchored onto the large board. Since my dimensions are similar to yours I thought I would let you know what advice Doug gave me. HTH