Burned Edges....

[Redman5006]

I see this come up a good bit lately. I'm very sure it's possible to overheat an edge at the factory, but how common is it really? Can an edge be ruined before it reaches the buyer? Will an edge that's been overheated need to be sharpened to get to the 'good steel'? I'm hoping some of the folks at Spyderco can chime in aswell. Thanks.

[Sharp Guy]

I currently have 60+ Spyderco knives and I've never had any issues that I'm aware of.

[VashHash]

Usually if the edge is "burned" it'll change color. Some people will reprofile a knife as soon as they receive it to get rid of the factory edge. I've seen claims that sharpening on a stone by hand without water can heat up the edge and ruin it. I've never experienced it myself. I don't think spyderco is shipping knives with "burned" edges.

[ABX2011]

I don't think sharpening by hand could get an edge that hot. Hot to the touch isn't hot enough. Would have to be at least 400 degrees and much higher for some steels.

[FK]

This is caused by sharpening by power belt which causes the very thin edge to exceed the tempering temperature (approx. 300F).
A new belt with aggressive cutting is very common contributor.
On some steels this will show as blue or discolored steel, many alloys have no visible indication.
It usually is very shallow depth and will quickly be removed with several sharpening cycles.

Many claim the "burned edge" problem when actually it is poor sharpening technique,,, rolled edge or burr that is very small and "does not cut very well".

I have owned perhaps over 100 Spyderco knives, never experienced obvious soft edges from overheating,,, have seen many very small stubborn burrs, especially on the newer specialty steels. Your friend is a 10x eye loop and strong direct light.


Regards,
FK
Member since Feb 17, 2001

[Chumango]

It is very easy to form a burr with power equipment. If the burr is only straightened rather than removed by the final sharpening steps you are left with a weakened edge. I suspect this contributes more to observed issues with factory edges than does overheating, though I don't know how often either actually happens.

[The Mastiff]

This is caused by sharpening by power belt which causes the very thin edge to exceed the tempering temperature (approx. 300F).

Some of the steels Spyderco uses can have tempering temps up near 1000 degrees F depending on which heat treat is used for that steel. The steels with red hardness (High speed steels, some stainless steels are up there too) generally are going to be pretty high.

I agree if the steel is changed by high enough heat some visual changes will be there. I'm not personally convinced that this "needing fresh steel" is applicable in every case of knives being sharpened on power equipment like pretty much all manufacturers use. They are aware of the limits of the steels and their manufacturing technique .

There is a chance of other factors being responsible for performance differences in two different knives that were sharpened differently but both ended up at 1000 grit for instance. I'm not really aware of any testing that determined there is truth to the old "need to get to fresh steel after the power sharpening" idea that seems to be a thing of common knowledge on knife forums.

Joe

[Redman5006]

This is caused by sharpening by power belt which causes the very thin edge to exceed the tempering temperature (approx. 300F).

Some of the steels Spyderco uses can have tempering temps up near 1000 degrees F depending on which heat treat is used for that steel. The steels with red hardness (High speed steels, some stainless steels are up there too) generally are going to be pretty high.

I agree if the steel is changed by high enough heat some visual changes will be there. I'm not personally convinced that this "needing fresh steel" is applicable in every case of knives being sharpened on power equipment like pretty much all manufacturers use. They are aware of the limits of the steels and their manufacturing technique .

There is a chance of other factors being responsible for performance differences in two different knives that were sharpened differently but both ended up at 1000 grit for instance. I'm not really aware of any testing that determined there is truth to the old "need to get to fresh steel after the power sharpening" idea that seems to be a thing of common knowledge on knife forums.

Joe

I feel the same way pretty much. Companies know the limits of their steel and take great precaution to protect their work. Making sure properly trained operators are in place is part of it too. I'm sure it happens, but not often. Also, seems like if a burned/overheated edge happens, it would be much deeper than just a few sharpenings.

[JD Spydo]

The only time I can ever remember experiencing a premium grade knife with questionable steel was over 20 years ago. It was in 1995 and I got a Benchmade auto model and I believe it was the model 2500 if my memory serves me well. And I'm in no way picking on Benchmade because I'm sure that a bad batch of any manufactured good can happen to any company for that matter. Because all of my Boguszewski Spikes were like razors.

But I couldn't get that knife to hold a good utility edge for anything. I was literally sharpening that knife almost daily sometimes. A good friend of mine had a son who wanted that knife really bad because he wanted an "automatic" and didn't really care about edge holding so I sold to him. I let him know it didn't hold an edge very well but he wanted it anyway.

I'm just wondering if an entire batch got a bad heat treatment? Because I sharpened this blade way beyond the factory edge. But I never remember any Spyder I ever had with that problem with.

[FK]

The Mastiff,

True, the M4 and similar tool steel series will have tempering temperature of 1,000F, these are very much less prone to edge burning and are designed to work at higher temperatures as cutting tools.
Several high volume posters on this forum and others have complained about "burned edges" with M4.
Very unlikely the manuf. process of final edge sharping with power driven belts will obtain those temp. ranges.

The most likely candidates for over heated edges are the simpler alloys with tempering temps in the 300F-400F range.

The fresh steel with new blade is very common with wood workers using Japanese tools with Hitachi "white" and "blue" steels, these are commonly heat treated in open atmospheres with oxygen available to decarb the steel surface.

Regards,
FK
Member since Feb. 17, 2001

[Crux]

Burned ends or edges are never a good sign unless it's brisket.

[Evil D]

I've definitely seen an improvement in edge retention and a reduction in chipping after reprofiling factory bevels. Whether that means they're burned or not I dunno. My 20CP Para 2 was practically unusable until I reprofiled it, it suffered significant visible chipping from cutting cardboard. That was years ago though and that knife was sharpened by hand on a belt so perhaps the automated sharpening has reduced those issues.

[Halfneck]

Most of these complaints I see on various forums I'd be willing to bet are due to pilot error. **** I've been sharpening knives freehand for close to 40+ years and sometimes I can't get a knife sharp. I just consider I'm having an off day and try again later - It happens.

About the only incidence of burned edges I recall was from Kershaw. I *think* it was with their early batches of knives using Elmax.

[J D Wijbenga]

I have noticed that edge holding often improves on new knives after the have been sharpened a few times. But, I do not have the equipment test the hardness of new edges. So why they improve I can not know for sure.

[jpm2]

I've had 1 knife from the factory that needed almost 1mm of edge removed before it would stop crumbling. It's anyone's guess what the cause was.

[Bpfohio]

I personally have a Rex 45 Para 3 that dulled after cutting 3 flaps off a box, any further attempt to cut the cardboard just resulted in tearing. Put it on the kme and it was soooft...sharpened easier than AUS8. I've talked to quite a few guys with the various Rex models and they've noticed similar issues and are attributing it to burnt edges at the factory. After the 3rd or 4th sharpening it seems to stiffen up quite a bit which lends credence to that thought.

[jpm2]

My Rex45 para3 has been excellent so far. Cardboard and wood have barely phased it.

[hackzogan]

I’ve had positive experiences with breaking down several cardboard boxes easily with my Rex45 para 3 thus far

[Redman5006]

It would seem that with steel being a conductor of heat that any over heating at the edge would go further into the steel that just a few sharpenings.

[ABX2011]

It would seem that with steel being a conductor of heat that any over heating at the edge would go further into the steel that just a few sharpenings.

Not necessarily, the thicker cross section takes longer to heat up.