This is old stuff but perhaps some of the members will benefit.. I dont like fingernail boards as for me they are too coarse so this is what I do'.
Cintact cement . Throw away brush , block if wood (cedar is good) , sandpaper grit of your choice.
Iuse 2 coats on the wood & one coat on the sandpaper,
Note the big old chisel
Hack away and you can get any shape you wish
Make a few of these in various grtis to keep on the shelf and cut whatever shape you need with a chisel