Knives- Sharpening and “burning out the temper”

[Selous]

I have wondered about this for a while but saw the following quote on another knife related thread.

Actually i suspect these grind backs are actually done high speed with a bench grinder over heating the blade and loosing its original heat treatment

My question is this…. If powered sharpening heats up the blade sufficiently to alter the heat treatment (presumably we are talking about annealing), why does the blade or edge not end up glowing red hot or at least hot to touch? Or is the concept of “burning out a temper” just a load of ill informed bull poop?

 

[Longstrider]

Bench grinders have killed more blades than hard work ever did.

01 tool steel is heated to over 800 C before being quenched in oil to harden it. At this full hardness it is not good for blades as it is brittle. It is then tempered for a period of time at around 220 C to effectively remove some of that hardness to achieve strength rather than be brittle.

If the steel is heated to more than 220 it will soften further. If you get it hot enough to go blue it will be softened a lot. If it glows red it will full anneal and be back at it softest state.

It's really easy to heat the thin steel of a knife edge far too much for it to be a good thing when regrinding 'finished' blades.

 

[Dorset Shakari]

This is why I use a Tormek.

 

[Tim.243]

I have wondered about this for a while but saw the following quote on another knife related thread.

Actually i suspect these grind backs are actually done high speed with a bench grinder over heating the blade and loosing its original heat treatment

My question is this…. If powered sharpening heats up the blade sufficiently to alter the heat treatment (presumably we are talking about annealing), why does the blade or edge not end up glowing red hot or at least hot to touch? Or is the concept of “burning out a temper” just a load of ill informed bull poop?

Not crabbing any of the knife makes just years of trial and error on sharpening many cutting edges.
Overheating a cutting edge is not just related to knives it just happens to be the tool used also a " Hot Subject"

Tool steel say a good quality Dormer twist drill which are mainly sharpened on a bench grinder and dipped in the tin can next to the grinder for the reason to keep them cool, if you wind it into the wheel and get it hot then it's cutting life will be short. Drills are not annealed you simply go back and repeat the process (this time keeping it cool)

Before tipped tools came along all grades of tool steel were profile ground or by hand, you need a 1.5mm o-ring groove
you grind it just to size with rake angles which it will have on 3 faces depending on what material.

A few different degrees in grind angles is nominal as you are cutting a piece of soft flesh, if you keep hitting bone all the time you will dull the edge no different to hitting a nail staple buried barb wire with a chainsaw.

In a blind test given 2 sharp knives to break down a haunch with a range of say 20 or 15 would be no different

These guys do it day in day out so in my book, he is showing new people so if they can do it the fully kitted gadget owning stalker should have no problem

If you want to learn more watch the video I did...!