Tiller blocks work very well, I wouldn't be without a set. I made mine from an aluminum bar, but I have seen them made from washers. They do require that the end of the limb be square, and they won't work with thick antler or horn overlays. I glue on a 1/16" phenolic overlay then use the tiller blocks to find center. After sanding the limbs to width I glue on the rest of the overlay. The only problem I've had with them is my first string wasn't strong enough and broke, it dented the limb and threw the tiller blocks across the shop. I actually found one block inside the drum sander.