I wouldn't go down quite that thin. What couple of pyramids I've made, i usually roughed them out about 5/8"-still barely bending, but leaves you plenty of meat to tiller it down. The last one I made wound up at 7/16" thick most of the way at 53#, so if I'd started it at 3/8", I would have been in trouble. Every piece of wood is different, so it pays to err on the safe side.