Burned edges from belt sharpening

[Maximumbob54]

I hear a lot that sometimes the edges from the factory are "burned" and you have to grind a certain amount and suddenly the edge starts staying longer. I've certainly seen some discoloration on blades from various brands over the years so I can see how this might be a true problem.

So my question is just how much steel would you expect to have to grind away?

 

[Obsessed with Edges]

I think it's highly variable as to how much needs to be ground off. Sometimes, and actually I think most of the time, just two or three light sharpenings will bring an improvement in edge stability.

I did have a lesson in patience with one inexpensive paring knife, years ago. I'd resharpened it multiple times over the span of weeks, or even months, and the edge would simply crumble away as soon as it was apexed. It wouldn't form an obvious burr, but instead would just crumble into dust when the edge was thinned past a certain point. I was tempted to assume it was completely worthless and just throw it away. But instead, I just put it away and forget about it for some time, until I was willing to have another go at it. After months of that approach, it finally took a decent edge that held up as I'd expect for simple kitchen stainless steel, and became a pleasure to use in the kitchen.

I'd not grind too much off at once though. I think the safest approach is just to take a little at a time, each time you tune up the edge. Most of the time, that has worked for me and it doesn't take too long to get the edge as stable as it should be. I think most heat-damaged edges are probably only lightly burned (not discolored, but weakened) very near to the factory apex. So in my experience, it usually doesn't take much to remove that damaged steel near the edge.

 

[Maximumbob54]

I guess that was a bit of a too open ended question. And I would definitely take of a minimal amount at a time each time to see how well it stays.

Maybe a better question should be, if you see obvious sign of discoloration then how much would you think you will have to grind?

Or maybe even if you do see discoloration maybe it's not even worth purchasing in the first place or should be returned to the vendor.

 

[Guy McVer]

Maybe a better question should be, if you see obvious sign of discoloration then how much would you think you will have to grind?

Or maybe even if you do see discoloration maybe it's not even worth purchasing in the first place or should be returned to the vendor.

I don't recall ever seeing an edge which has been discolored by overheating during the factory grinding process. I have encountered plenty of edges which had benefited from several sharpenings in order to get down to the good steel which wasn't ruined by that process. Some of them were quite bad in fact, and took a lot of sharpenings before they started to hold up, but there was still no apparent discoloration.

I would therefore assume that if you see any discoloration, it would probably mean that severe damage to the heat treat was done, and I wouldn't buy that knife or I would return it if it had been sent to me in that condition. But it might depend on the characteristics of the steel. Maybe some steels are more prone to discoloration that others. I wouldn't know because I don't buy a lot of expensive knives. I prefer cheaper steels because they are easier to sharpen, and I just stay on top of the edge so that I never have to spend long amounts of time fixing the edge back up.

I think most heat-damaged edges are probably only lightly burned (not discolored, but weakened) very near to the factory apex.

I think your answer is right here. This poster usually knows what they are talking about, with few exceptions.

 

[Obsessed with Edges]

I guess that was a bit of a too open ended question. And I would definitely take of a minimal amount at a time each time to see how well it stays.

Maybe a better question should be, if you see obvious sign of discoloration then how much would you think you will have to grind?

Or maybe even if you do see discoloration maybe it's not even worth purchasing in the first place or should be returned to the vendor.

I think personally, my approach would usually be the same. Sharpen it a few times and see how it responds. Heat-damaged steel can change in various ways. The crumbling issue I saw struck me as very weird in itself and not typical as compared to all the others I'd seen, which usually just left the steel softened (annealed) near the edge in a manner that made it flimsy, but not crumbling away. This is the sort of damage that's usually only in the steel very near the edge and can be sharpened away relatively easily.

I could see other forms of heat damage or bad heat treat making an edge brittle and more prone to chipping issues or even breaking the blade. Depending on how bad that is, it may still be usable for lighter, simple cutting tasks, but might be prone to chipping or breaking in heavy chopping or twisting of the blade in the cut.

I would agree though, that in the case of a new purchase, if I see discoloration in the steel, I'd likely just return it to the vendor or maker and not tempt fate.

 

[kane22]

I've never seen one that was really discolored, I'd return it if I could. I think 3 normal sharpening should get you to good steel with just a normal burnt edge. I'm sure it could vary with the steel and the heat treat

 

[elevator man]

I have a thread on this with a particular knife i have in k390 over in the spyderco sub section. My first 3 or maybe 4 edges had a lot of chipping. Very much compared to 2 identical knives in identical use. Leading me to believe the edge was overheated and too brittle. Its a tough steel that shouldn't be chipping. Its last 2 edges really mellowed out, not chip free yet but definitely less chipping. I'm going to update that thread in awhile once I've got more time with that knife. But I 100% believe a steel can be overheated when ground at the factory leading to subpar performance until you sharpen past that and get to good steel.

So, in my experience could be at least 4 or 5 sharpenings to get to good steel.

It's also more common this is not a problem. I have a few other knives from the same maker in same/similar steels that were perfect from the factory edge and never had a problem.