I practice on an 8inch Mercer and I don’t really feel a hard burr anymore, instead it’s just gummy. Is there a ball park number as to how many mm one can remove before the metal too soft to mess with. I thought I read somewhere that the temper is only along the edge but now I can’t find any info on this. I’d love to not have to spend money on practice knives just cause I only have a few mm of practice space so please enlighten me.