The best way to sharpen by hand. Don't buy sheets and don't try to cut them into blocks. Don't buy expensive pre-cut squares and glue them on. Round orbital sanders are commercially available, inexpensive, very efficient, available in all grits, and easy to attach to this block. They don't come off until you want them to, and then you just take them off and replace them with nice sounds and textures. If you have (or even if you don't) have a random orbital sander with Velcro attachment pads (like Velcro), it will outperform all other devices and save you money in the process. I combine this with the 3M 05791 Hookit Soft 6" Disc Paddle when I need flexibility.