This morning I was in the process of grinding a 55* Whitworth form threading tool and got to thinking about my dad's habit of setting a newly ground tool bit aside for a few days after grinding and the final polishing with a stone. He claimed a HSS tool bit treated like this would last longer between re-grinds and cut better. I've been told the same thing by two long retired tool makers for whom I have a great amount of respect. My dad passed away four years ago and I inherited many of his machinist tools (which I treasure) and as well quite a number of 1/4 and 5/16 HSS tool bits which he had ground and polished for particular jobs. Each one of the tool bits are still razor sharp and on the occasions when I've used them they've cut steel like a hot knife in butter. Each time I've used one I've touched it up with a stone after I'm done and I've never seen any pitting or eroding at the tip. Those bits I grind and polish and then put right to work invariably need regrinding after several hours' work. When I get done polishing the 55* threading bit today I'm going to set it aside for a few days before using it and see if it benefitted from its "rest". Has anyone else heard of this?