Does Sharpening with a Grinder Ruin Your Edge?

Nathan the Machinist said:
You can take a new unsharpened knife and get it sharp on Waterstones in about 5 minutes!?
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Yep! Though it depends a lot on how thick the edge is. You can certainly remove material very quickly pushing it back and forth on a 240 grit waterstone, with pressure.
 
LCoop said:
Proves exactly what I've thought with a lifetime of field experience but could never provide data for.
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This sums up my thoughts as well. I would have no way to prove it empirically, but in my experience powered sharpening yields some wicked sharp edges that dull relatively fast with use. It's nice to see the test data on this.
 
Thanks larrin great article
I've never sharpened on a belt I felt I needed to learn how to use stones
It takes a bit of time and some fine motor skills to get a good edge on stones
I wonder would this be relevant to us who grind our edges to near zero on a grinder before we sharpen?
Are our near zero edges over tempered just from grinding?
 
Hi John, i would be very cautious approaching a zero-edge. Best would be starting using coolant on hardened blades.
Even just spraying the (slow-speed) belt with water will prevent overheating enough to avoid spoiling the HT. Just keep the belt wet and you shouldn't worry.
It will be very difficult to assess if you can get by if you dry grind up to a certain edge thickness and then finishing with coolant/whetstones...Larrin showed us those tap's pictures reporting HRC at different depths. In pratice you might not be aware if you lost a couple points Rc, but you know you can prevent this by using coolant.
 
stezann said:
Hi John, i would be very cautious approaching a zero-edge. Best would be starting using coolant on hardened blades.
Even just spraying the (slow-speed) belt with water will prevent overheating enough to avoid spoiling the HT. Just keep the belt wet and you shouldn't worry.
It will be very difficult to assess if you can get by if you dry grind up to a certain edge thickness and then finishing with coolant/whetstones...Larrin showed us those tap's pictures reporting HRC at different depths. In pratice you might not be aware if you lost a couple points Rc, but you know you can prevent this by using coolant.
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Its amazing how much help a squirt bottle is with a little dish soap in the water.
 
I get my bevels pretty close with my 2x72 and set the final edge with a 600 CBN plate. The next step is where I'll probably get some head scratches. I do my final polish/strop on a slotted paper wheel. The slots blow air onto the blade. You can put your bare finger on it and it won't burn. Very light pressure.

I get consistently sharper and longer lasting edges, than when I strop by hand. Unless I'm using my high grit water stones and finish on a newspaper strop.... which is nice for showing off but impractical for most situations.
 
there is definitely skill involved in sharpening off the belt.
I’d say that it’s possible to have an edge off the belt equivalent to a stone finished edge but, it is also more likely that a lot of knives are “ruined” at the edge due to... lack of awareness?
 
Nathan the Machinist said:
You can take a new unsharpened knife and get it sharp on Waterstones in about 5 minutes!?
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I find it takes me about 1/2 hour with diamonds initially, then ceramic waterstones after. Granted, I’m using higher hardness, or higher alloy steels, but it takes time to get a refined edge. I’m not going to cut corners here. I want people to be amazed when they use the knife the first time.
 
First, Thank you Larrin for the article.

A question here about belt sharpening on a 2X72 which is how I normally sharpen blades. While running belt in reverse with edge up, belt speed around 300 to 400 SFPM the first grit will be perhaps 400 grit to thin edge and create a burr. This is done with finger/thumb on blade where it never even feels warm and no sparks are ever seen. Might hit with 600 to 800 grit lightly. Then a belt turned inside out with green compound to take the burr away. The knife will usually shave, slice phonebook pages, etc nicely at this point. With the edge never getting a warm feel and no sparks ever thrown - is there still danger of heat damaging the HT? Perhaps there are things happening at the microscopic level I'm not aware of?

As usual, I'm here to learn with an open mind.
 
Guys , this on picture from Larrin article is /magnified / ONE tooth from HSS tap ...And if that is not from HSS tap with one foot Dia........For how much damage we are talking about ? 5-10 micron ?

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Too bad that there is no data how deep damage/softening is on that knives used in test ? They could measured the width of the blade prior they test them and then resharpen blade , repeated test until it does start to keep edge as it should ..........and measure how much steel was lost ?
 
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Larrin said:
I think the title introduces this one well enough.

https://knifesteelnerds.com/2019/04/08/does-sharpening-with-a-grinder-ruin-your-edge/
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Reading article and looking picture from that HSS tap it is obvious that when steel was over tempered there must be some color ? If that is right........I have access to a very powerful microscope to see color change od edge ? I would like to make some test with different sharpening , I have plenty of blade in different steel to play with them ?
 
Natlek - that's a great idea. Looking forward to your results. What power is your "very powerful" microscope? My unit only goes up to 90X with the 2X eyepiece in.
 
Ken H> said:
Natlek - that's a great idea. Looking forward to your results. What power is your "very powerful" microscope? My unit only goes up to 90X with the 2X eyepiece in.
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I have no idea , it is not mine ......Friend of mine work in Clinical & laboratory if I use right words ? They have there are lot of that stuff...
 
The color difference comes from etching of the microstructure.
 
It takes me 5 minutes just to decide what stones I want to use and drag them out and prep them! Ha ha! But I have always loved sharpening knives on stones since I was a kid. Just something about it that I enjoy. I’m always offering to sharpen friends’ and acquaintances’ knives gratis. (I forget proper plural punctuation)

A lot of us on BF are familiar with the work Roman Landes has done on powered vs non powered sharpening. For those that aren’t, a quick “inter webs” search calls it up. His conclusion, heat buildup happens extremely fast, especially on the micron/submicron levels we are routinely dealing with in knife edges. The color change (by eye) may not be visible, but the damage can certainly be there. IIRC, he did some sort of experiment where he was able to imbed tiny thermocouples into the corner of a steel block and then got a reading of the heat buildup that occurred by abrading it. Something like that anyway. And if I correctly recall further, his recommendation was that any sharpening (powered or by hand), should be done with lubricant. Don’t hold my feet to the fire on the veracity of that last statement concerning “hand sharpening is best with lubricant”....(or at least allow my feet to be kept flush with water if you do!)
 
Willie71 said:
Hmmmm..... my response in that thread was identical to what I posted above here.
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Yes, there have certainly been some posts in the past that show that people have worried about this.

I think there have been at least a few threads about sharpening in the past couple years and frequently some sort of belt technique has been mentioned.
I have been using the "slack belt" method myself for the most part based on reading those threads. I use a Wicked Edge system when I'm afraid of messing up the tip on daggers, but I didn't realize it might be helping performance. I don't sell any knives, so nobody will call to complain about edge retention, but I still want to get the best out of what I make.
 
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