Strage results when sharpening my Shiro 95T

seeverscpa

seeverscpa

Joined
May 19, 2015
Messages
349
I replaced the factory edge on my Shiro 95T, using my Ken Onion belt attachment, at 20DPS. As I was moving along through the grits, I noticed "chips" appearing near the tip of the blade. It was as if when I removed the burr from one side, it would take a small bit of the edge with it. Thus my completed edge has chips in it, where the metal had broken away from the edge. I am running the belts at lower speeds, and nothing ever heats up more than lukewarm. I started with the medium grit (P1000), which is sufficient to start this process, and I was able to form a burr in a relatively short time.

What would cause these chips to happen?
 
I got strange results when sharpening my neon zero for the first tim; I later put it down to being drunk at the time and scratching the base of the blade.

We live and learn.
 
Does sound like heat damaged steel. OR, the steel is harder & more brittle than it should be, by the heat treat.

I can't find any published hardness specs for these knives, so that's a question in itself. As expensive as they are, that shouldn't be an unknown.
 
I cringed when I read about sharpening a Shirogorov on a cheap belt grinder.

Larrin's article -- linked to by 000Robert -- seems to give the answer.

From Larrin's report, I'd guess that you softened the edge by overheating it. Rather than the grits scraping the surface of the steel, they dug into the softer steel and carved out troughs that created a chip-like effect. But that's my guess.

I'd hand sharpen out the bad steel to a 15 dps edge, and then use a 20 dps stone angle to resharpen with a micro-bevel. After that, resharpening the micro-bevel will go even faster than that belt grinder. And the edge will perform much better.
 
Twin, thank you for your insight. Would a more expensive belt grinder have not caused this problem? (Pure sarcasm, I do understand your point)

There is no way I overheated the blade, it's just not possible in this case. The speed of the belt was at its lowest setting, and wouldn't we see some kind of temp lines forming if the blade got as hot as I think it needs to get to soften the metal? After reading the steel nerds article I have to admit that anything is possible...

I'll take a pic of the offending chip and it is clearly a chip that broke off, not so much as a carved out trough. Shiro does some proprietary finish on his blades, it is not a stone washing per se, but it looks like one. I was thinking that it was in fact some part of this surface finish coming off and taking some of the edge with it. The particular knife steel is M390.

Regarding the hand sharpening, A) I do not have any good experience with table stones, and B) I have an Edge Pro, and the Shiro's are full-flat grinds, thus there is no existing blade shoulder to clamp on to. achieving the proper angle is not an exact science.

Twin, I will try your 2-step suggestion and report back.

Thanks for the guidance all.
 
seeverscpa said:
...There is no way I overheated the blade, it's just not possible in this case. The speed of the belt was at its lowest setting....
Click to expand...
I can almost guarantee that you overheated the very tip of the edge. Any and every dry grinder on the market will do the same thing. You definitely wont easily overheat the whole blade, but the tip of the edge will be blown in microseconds.

I'm not saying this is necessarily the reason why you're experiencing problems with your edge chipping, but it's worth knowing the facts.

Remember that an edge is an edge because it is only a fraction of a micron thick when very sharp. Now remember the laws of thermodynamics. Remove metal fast (even on the lowest setting of ANY dry grinder), and it warms up FAST. (Fraction of a second fast)

You'll never ever know you overheated the edge, because it is microscopically thin. If you actually feel any heat where you're holding the blade, remember that heat has transferred from the edge, which is a tiny surface. The temper temperature, or even austenizing temperature in some cases, has been exceeded in a fraction of a second and your metal at the tip of the edge has now gone through phase changes and your heat treat in that tiny part of your blade is ruined.

This is why most factory ground knives (dry sharpened on a grinder or belt, post heat treat) will almost always get an improvement in its edge holding ability after a few whetstone sharpening sessions when you've removed the overheated edge.
 
Last edited:
You said you have an EdgePro, use that to refinish/profile the blade and that will fix and possibly prove this “hypothesis “
 
Depending on the thickness of the blade, with a full flat grind, if you set it at 20 degrees it will give you about 17 degree bevel.
 
sickpuppy1 said:
...and possibly prove this “hypothesis “
Click to expand...
Not a hypothesis at all, it's been proven over and over and most recently written about and tested by Larrin Thomas.(The father of Magnacut)

000Robert 000Robert posted a link above, but in case you missed it, here is a link to the most recent article on the subject.

knifesteelnerds.com

Does Sharpening with a Grinder Ruin Your Edge? - Knife Steel Nerds

You have to sharpen a new knife a few times to get it cutting well. Right? Or do you? Are knife manufacturers improperly sharpening their knives?
knifesteelnerds.com knifesteelnerds.com
 
777 Edge said:
Not a hypothesis at all, it's been proven over and over and most recently written about and tested by Larrin Thomas.(The father of Magnacut)

000Robert 000Robert posted a link above, but in case you missed it, here is a link to the most recent article on the subject.

knifesteelnerds.com

Does Sharpening with a Grinder Ruin Your Edge? - Knife Steel Nerds

You have to sharpen a new knife a few times to get it cutting well. Right? Or do you? Are knife manufacturers improperly sharpening their knives?
knifesteelnerds.com knifesteelnerds.com
Click to expand...

LOL! Your link is the same link as mine.
 
So I took Twin's advice, and I got a fairly polished final edge on the Shiro, and those chips near the tip are long gone.

Sick puppy, on the EdgePro, I compensate for the angle deviation due to the FFG nature of the Shiro blade, to get back to a 20 DPS. The FFG angle on the Siro came up at 9.7 inclusive with my angle cube, so I need an angle setting of 24.85 degrees to get to 20 DPS on the edge of the Shiro when laying the FFG Shiro blade flat on the Edge Pro table. I set this angle by taking the angle of the knife table itself (30) and adjusted the stone angle to be 5.15. The difference in those two angles is the 24.85 edge angle that I need to get to 20 DPS on the Shiro.
 
Last night I repeated the process. As I looked at the edge I produced the other night a little closer, I thought I could do a better job. So I went back starting with a 200 stone and moved through 400 600, 800, 1000, and finally the strip. I really took my time doing it, and used plenty of water. The results were even better. I don’t have a beaming shiny edge, but it’s pretty damn polished and the edge is screaming sharp per my definition. The tip to Ricoso edge of the knife push cuts phonebook paper with zero effort.

Something else I noticed using the belt grinder versus the edge pro water stones, is that no matter what I always ended up with a convex edge using that bell grinder, due to some of that bend you can impart on the belt when you’re pushing down on it. I thought I could avoid it by not pushing as hard but there’s always a little bit of flex in the belt when you’re grinding and that leads to that convex edge.

I want to keep the belt grinder for garden tools and other shit like that, but I think I’m totally committed to using the water stones from here on out, even such that I ordered some Chosera stones and some polishing tape for the edge pro.

I’ve been watching some videos with that Tourmek T8, and damn does that not look like a sweet piece of machinery. But after the machine and accessories you’re getting close to like almost a $1000 worth of kit. Anyone using this system?

I want to thank everyone for the great advice and guidance, it is accomplishing to put the suggestions into action and have some really good outcomes.

On a slightly unrelated topic. I just picked up a new Shiro quantum and I noticed the actual bevel is so small as it relates to the face of the blade, it’s something like an eighth of an inch bevel at what I understand to be 20DPS. How does the maker of the knife get that bevel so small? It’s clearly a belt grind, but I have to assume they must be using a jig or some form of automated sharpening to be that precise? Take a look at the magnified pic of this edge I’m taking about. That’s like 1/8”.
 

Attachments

  • 863CA5FE-D8CD-4DF6-9AA5-AB85A2D949F2.jpeg
    863CA5FE-D8CD-4DF6-9AA5-AB85A2D949F2.jpeg
    1.5 KB · Views: 29
"On a slightly unrelated topic. I just picked up a new Shiro quantum and I noticed the actual bevel is so small as it relates to the face of the blade, it’s something like an eighth of an inch bevel at what I understand to be 20DPS. How does the maker of the knife get that bevel so small? It’s clearly a belt grind, but I have to assume they must be using a jig or some form of automated sharpening to be that precise? Take a look at the magnified pic of this edge I’m taking about. That’s like 1/8”."
Click to expand...
The width of the bevels, as compared to the primary (overall) grind of the blade, are a function of the sharpening angle AND the thickness of the steel at the edge.

For a given fixed sharpening angle, a thinner blade will have narrower bevels and a thicker blade will have wider bevels. So, if you notice the bevels are still quite narrow, even when sharpening at a fairly acute angle, you can conclude the blade is ground very thinly near the edge - that's almost always a good thing to see, and is an indicator of a blade that should perform very well as a fine slicer.
 
Last edited:
I don't buy the "all grinders ruin all knives" argument. I've sharpened a whole lot of blades on a belt grinder and am not aware of any with heat related damage. Maybe it happens with some steels, in some knives, under some circumstances. But the idea that a belt machine always ruins blades? It simply can't be true because 99% of all knives produced would be "ruined" right from the factory.

I also would like to point out that if you use a guide, it is possible to make extremely light contact with a belt. So light at you can hear a rhythmic pattern to the contact as only little bits of the belt touch the blade. I normally do this as I'm finishing a blade in order to reduce the burr as much as possible.

Brian.
 
bgentry said:
I don't buy the "all grinders ruin all knives" argument. I've sharpened a whole lot of blades on a belt grinder and am not aware of any with heat related damage. Maybe it happens with some steels, in some knives, under some circumstances. But the idea that a belt machine always ruins blades? It simply can't be true because 99% of all knives produced would be "ruined" right from the factory.

I also would like to point out that if you use a guide, it is possible to make extremely light contact with a belt. So light at you can hear a rhythmic pattern to the contact as only little bits of the belt touch the blade. I normally do this as I'm finishing a blade in order to reduce the burr as much as possible.

Brian.
Click to expand...

Nobody said that "all grinders ruin all knives". But 'dry belts' will ruin the heat treat of your 'edge apex'. I'm wondering if you actually read any posts.
 
000Robert said:
Nobody said that "all grinders ruin all knives". But 'dry belts' will ruin the heat treat of your 'edge apex'. I'm wondering if you actually read any posts.
Click to expand...

Well, I'm not trying to be combative here. I admit my post was kinda short.

But the idea that all dry belt grinders ruin the heat treat of a knife is also rather hard to believe. That means every Spyderco ever shipped has a burned edge. Do you believe that? I don't.

Brian.
 
bgentry said:
Well, I'm not trying to be combative here. I admit my post was kinda short.

But the idea that all dry belt grinders ruin the heat treat of a knife is also rather hard to believe. That means every Spyderco ever shipped has a burned edge. Do you believe that? I don't.

Brian.
Click to expand...

Larrin's blog documented numerous studies that show edges ground on a dry belt grinder do not last as long as edges sharpened by hand on stones. It's worth a read.

I don't think that dry belt grinding ruins all edges, but they do soften edges enough to reduce their performance. And it's easy to actually ruin an edge that way if you lack experience.

Here's a quote from just one of the experts quoted: "Roger Hamby of CATRA also tells me that in their testing of edge retention that over 75% of the knives they test suffer to some degree of edge softening due to the sharpening process. He reports that nearly all manufactured knives have the problem, while hand sharpened knives generally do not."

Experts will do better than us amateurs, but the issue is real.

Here's a photo from Larrin's blog that shows changes in hardness (Rc) after an edge was ground with a dry belt.

1632618064471.png

In other tests, a difference of 5 Rc was measured -- and it could have been even more at the apex, where Rc cannot be measured.
 
You must log in or register to reply here.
Back
Top