"Resting" HSS tool bits after grinding

[Guero]

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?

[DR]

With all due respect to your Dad and others, this may be one of those old wive's tales that gets passed around for no other reason than because it came from an old retired machinist.

Your own experiences may be just coincidence. It'll take some better evidence to convince me.

[SGW]

I'll believe it when somebody does a controlled double-blind test.

[vinito]

I've never heard that one. Metallurgy is not my stongest point, but I wouldn't think that much significant change happens in steel (once it cools down) within a day or two.
It might just be organized machinists not wanting to explain how they can be so patient.
I've been wrong before. What time is it?

[Mark Jones]

I was watching a program about plane construction and they did just that with the alloy panels the plane was made out of.
something to do with the ductile-ness if i remember right.
but that is not hss ...so I dont know.
all the best..mark

[Guero]

Well, my dad also did such things as weeding the garden and cutting down trees (for firewood) during the waning moon and planting and grafting during the waxing moon. He was an A&P mechanic with a doctorate in structural engineering, could play any musical instrument by ear, wrote poems, and rode motorcycles all his life (when he was 78 he and another old-timer drove from North Carolina to Guatemala and back on motorcycles and had a bodacious good time). Oh, and he spoke Spanish and high German as well as English. I've learned through the years that despite my doubts the various things he's told me inevitably turn out to be true. Since I'm the youngest of his five children I ended up with the least of his abilities.

On the HSS steel he explained that the grinding "excites" the molecules and letting it rest a few days before putting it to work gives them time to settle down.
Ben Rich

[Allan Waterfall]

Ben,

Could depend on the grade of HSS he used.

Perhaps it would be better to sharpen two pieces for ordinary turning,use one and let the other "rest" and see which lasts longer in use.

Hard to tell screwcutting as its a long time between sharpens.

Allan

[Forrest Addy]

Good way to have 8 hours more spare time 5 days a week if you boss catches you.

[moldmonkey]

Could it be for stress relief? Like in seasoned cast iron. Don't know just throwing it out there.

[pete913]

I can't say, cause I haven't tried it, but anythings possible. I remember a former boss of mine, who's judgement I respect, telling me that the only way to machine a rough cast iron angle block so that it didn't move around after finishing, was to rough mill it, toss it outside for a year, through one of our very cold winters, and then finish grind it.