The bond of the glue between all of the different materials wouldn't be an issue with a shaft of metal running through the handle (which I'm assuming a spear would have). I have a couple of knives my granddad made toward the end of WWII that have handles (grips) made of stacked wood, brass, aluminum, copper, leather, and plastic (poker chips). They are all held together on the shank of the knife, and whatever glue Grandpa Bill used, it's still holding They're not lathe turned - they were shaped on a belt sander, I believe - but a wood lathe could handle all of those materials.