Grinding for hours...

How long does it take you to grind a typical 4 inch blade?

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A quick follow up. I haven't ground any more Niolox. I'll leave that for the time being. :D

But I have received some 14C28N that's been cut and profiled. It'll be interesting to see how it behaves during grinding.

I'm pondering whether I should pre HT grind it or not? It's 3 mm thick and in the shape of a western gyuto. What do you think?

I also had a Nakiri ready to grind, and tried a new grinding approach, based on the answers in this thread. Keep in mind, it's O1, so a lot easier to grind than Niolox, but it's 4 mm thick and I ground it post HT.

I managed to get it ground to A100 in less than an hour. That's progress. And there's a lot of meat to grind away on a 4 mm Nakiri, it tapers to 1,3 mm at the point and 0,1 mm at the edge. It also has a convex grind towards the edge.

Nevertheless, the secret to my success: I stopped caressing the steel and instead actually ground it. Since I grind wet I can put a lot of pressure on it. It did marvels with the speed. New belts and pressure seem to be the solution.

The result (I also handsanded it to 800 grit).
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Speed ....that s all you need ............and fresh belt . Speed , faster as it can .I work on my belt grinder to run over 60-70m/s .... :D This is 65HRC 1.4mm thick 1.2519 steel . Sand paper is grit 40. On 40 m/s its look like 400 finis :)

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Tom Lewis said:
Now, many years ago David Boyle used to advertise some kind of cobalt blade. I remember there were advertisements of him using a blade of that material to cut 1" hemp rope. He had a whole pickup truck full of cut pieces and was still cutting. A customer got one of those blanks for me to grind a knife out of. It was 1/8" thick. I couldn't believe how long it took to grind the bevels. Sharp belts just didn't want to cut it. I wouldn't have believed it if I hadn't tried it. That was the one and only blade I ever made out of that material. Sounds like you are using a similar steel.
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IIRC Boye's dendritic cobalt alloy is a lot like Stellite 6k or Talonite, but I think he also casts it to shape.
 
It typically takes me about 10 minutes to rough grind a blade with a fresh 60 grit belt.

At this point, as long as my edge is centered and my grinds are close, I'm happy. You don't need absolute perfection at this stage.

The time for finish grinding varies based on the intended finished grit, and any issues that might come up during the process.
 
cool thread! I spent 2 Hours last night to take an 8" blade down to final thickness. This was from 2.5mm thick hardened steel. I ground off the scale, and roughed in bevels with a 50 grit 967. Took the bevels up to the spine or close to with about .020 behind the edge with two 80 grit 947s. Then I convexed the whole thing with a very worn A300 structured trizact belt...and then used another 80 grit 947 to get the distal taper and very thin tip I wanted. This is the "dip in the water bucket after each pass" method so it is kind of slow. The time isnt too bad but the real killer for me is using about 20$ in belts just to get to a roughly ground blade.
 
Scale is a bit of a pain to grind off. I've found an overnight vinegar soak to eat off the scale makes the grinding easier.
 
FWIW, I rough ground 12 knife blanks last night in 3 hours. All 4-6" blades. 6 flat, 6 hollow. .125-150 stock. 36 grit, 60 grit, 120 grit. 2 were prehardened AEB-L. 2 soft 3V, 6 soft 80CRV2, 2 soft AEB-L.

I'll do more work to the 3V knives before heat treating. At least to 400 grit.
 
kuraki said:
FWIW, I rough ground 12 knife blanks last night in 3 hours. All 4-6" blades. 6 flat, 6 hollow. .125-150 stock. 36 grit, 60 grit, 120 grit. 2 were prehardened AEB-L. 2 soft 3V, 6 soft 80CRV2, 2 soft AEB-L.

I'll do more work to the 3V knives before heat treating. At least to 400 grit.
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That's impressive! And it gives me more reason to practice and get better at it, thanks for sharing.

May I ask how many belts of each grit you worn out during this three hour grinding frenzy?
 
I used up two 36 grit blaze belts (trying blaze again and I still don't like them), two 60 grit combat abrasives ceramic belts and hard to say on 120 grit because I used a couple different ones between the knives but didn't throw any out. By time I'm at 120 grit I'm not taking much material, just removing scratches. I use up 120s faster post heat treat.

Mind you none of these grinds are perfect. They're truly a rough grind and will need to be refined post heat treat. But at this stage I'm just trying to get most of the material I want gone, gone, while leaving enough edge thickness to hit my final geometry post heat treat.

Basically the same way I would make a punch or die. Some dimensions or features I want very close before heat treat, like flatness and parallelism, to be a reference post heat treat. But the majority of the work is just material removal. I also don't care at this stage if I get the blade hot enough to color. I only care if I burn my fingers :D

Also, the flat grinds were ground wet. The hollows dry. I haven't figured out how to prevent water from flinging off my belt onto my mask and obscuring my vision with the wheel yet at high speed. But for whatever reason that doesn't occur when grinding on my flat platen. And it definitely speeds up the process.
 
kuraki said:
I used up two 36 grit blaze belts (trying blaze again and I still don't like them), two 60 grit combat abrasives ceramic belts and hard to say on 120 grit because I used a couple different ones between the knives but didn't throw any out. By time I'm at 120 grit I'm not taking much material, just removing scratches. I use up 120s faster post heat treat.

Mind you none of these grinds are perfect. They're truly a rough grind and will need to be refined post heat treat. But at this stage I'm just trying to get most of the material I want gone, gone, while leaving enough edge thickness to hit my final geometry post heat treat.

Basically the same way I would make a punch or die. Some dimensions or features I want very close before heat treat, like flatness and parallelism, to be a reference post heat treat. But the majority of the work is just material removal. I also don't care at this stage if I get the blade hot enough to color. I only care if I burn my fingers :D

Also, the flat grinds were ground wet. The hollows dry. I haven't figured out how to prevent water from flinging off my belt onto my mask and obscuring my vision with the wheel yet at high speed. But for whatever reason that doesn't occur when grinding on my flat platen. And it definitely speeds up the process.
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kuraki, a few questions if you don't mind...

- what speeds are you grinding at?
- have you used the 984f cubitron II's in 36 grit and how do you like them compared to the blazes?
- with water flinging up in your face, where is it coming from and do you have any 'mud flaps' to prevent this?
 
1- Rough grinding pre-heat treat I generally grind at 4500 SFM. I typically slow down to 1500-2500 after heat treat, but it really depends on the knife, the grind, the belt, etc. It varies quite a bit more than rough grinding. Heavy pressure rough grinding and light pressure finish grinding.

2- I've used 984s in every grit and while I think they're the best belt available on the market I don't think they're the best value on the market and I've primarily switched to the Combat Abrasive ceramics bought in bulk (40% less than Pop's price for 984s). A 984 will run efficiently for longer but not 40% longer. My evaluation is that cu/in material removed per dollar spent is best with the CA (at bulk pricing). I was just trying Blaze again since so many people seem to like them and I thought maybe I hadn't given them a fair chance. My experience with them is that they lose their initial bite quickly and then get too hot too fast even though they're still removing material well.

3- Water coming from a mister. I don't have any mud flaps in place yet as most of the grinding I've been doing wet was flat platen, and for whatever reason the belt sheds the water down (I'm guessing due to the small 2" wheel causing a right angle, where the 12" wheel is a more gradual loop). But a well placed flap would likely do the trick.
 
Have you tried the yellow 50 grit cubitron 967s? I was getting atleast 4x the life as the cubitron 984s while grinding hardened stainless. Grinding annealed steel they seem to keep their bite longer than anything else i have tried.
 
Last year I tried a couple when I was grinding some 304 stainless san mai blades. They did seem to hold up well to 304 stainless, 2x as long as Blaze (this is why I was reevaluating blaze belts again, didn't think 304 was a good example of their capability). Since I do so little currently, I have not purchased any more.
 
kuraki said:
1- Rough grinding pre-heat treat I generally grind at 4500 SFM. I typically slow down to 1500-2500 after heat treat, but it really depends on the knife, the grind, the belt, etc. It varies quite a bit more than rough grinding. Heavy pressure rough grinding and light pressure finish grinding.

2- I've used 984s in every grit and while I think they're the best belt available on the market I don't think they're the best value on the market and I've primarily switched to the Combat Abrasive ceramics bought in bulk (40% less than Pop's price for 984s). A 984 will run efficiently for longer but not 40% longer. My evaluation is that cu/in material removed per dollar spent is best with the CA (at bulk pricing). I was just trying Blaze again since so many people seem to like them and I thought maybe I hadn't given them a fair chance. My experience with them is that they lose their initial bite quickly and then get too hot too fast even though they're still removing material well.

3- Water coming from a mister. I don't have any mud flaps in place yet as most of the grinding I've been doing wet was flat platen, and for whatever reason the belt sheds the water down (I'm guessing due to the small 2" wheel causing a right angle, where the 12" wheel is a more gradual loop). But a well placed flap would likely do the trick.
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Great info thanks for answering my questions. I grind around 1800fpm post ht as well so I was curious because it makes a ton of difference in the belts selected. I agree about the 984's, I have been testing CA's belts out recently and so far have tried their Sic, Al oxide x weight, and the 60/120 ceramics. The 120's seemed to perform excellently and were very comparable to 3m's 947 (similarly priced as well), but I didn't like how the 60's ground (only tried one belt, will snag more to give them another shot). So far the absolutely best belt for grinding under coolant in the 60 grit range has been pheonix abrasives yellow premium ceramic, it fractures perfectly and lasts for a good while (6 grinds post ht, was only getting 3 grinds out of the 984f's).

yes, flaps make all the difference in the world =)

Oh, and I tried the 967's a couple months ago at Pop's recommendation, but didn't like them at all... seemed to die off in cutting pretty quickly and the blade got noticeably hotter much quicker than normal. They are also not rated for water (even though they seemed to work ok in this regard). just my .02
 
I finally got around and tried the 14C28N stainless steel. It was like night and day compared to the Niolox. I pre-HT ground a 5 inch blade (3 mm thick) to full flat in less than 10 minutes with 60 and 120 grit VSM 870.

As per advice in this thread I went high speed and high pressure. It only took a couple of passes to take it to pre HT thickness and height (I took it to 0,4 mm).

One of my problems seem to be the fact that I've ground all my blades post HT. For some blades (thin) that makes sense, but it wastes a lot of belts and time to do it on all blades. I'll try to do as much grinding pre-HT as possible. We'll see just how much when I dial in the HT for the 14C28N.
 
Another technique for getting material ground away pre heat treat is to just grind a shorter bevel than the finished knife will end up with, maybe half the finished height. That leaves you a nice thick and flat spine to clamp between your plates when quenching to avoid warp, but you're half done when you start post heat treat grinding.
 
kuraki said:
Another technique for getting material ground away pre heat treat is to just grind a shorter bevel than the finished knife will end up with, maybe half the finished height. That leaves you a nice thick and flat spine to clamp between your plates when quenching to avoid warp, but you're half done when you start post heat treat grinding.
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That's another great tip. Thanks!
 
I will say the 967's much better at grinding hardened vs annealed steel, have no idea why, they really heat up the annealed stuff so fast. Still cut great with heavy pressure though...I didnt quite grind bevels in 5 minutes but I got it down to 15 anyway. Banged out a few 4 inch-ish blades this past weekend. MY last 20 or so knives has been grinding all hardened stock. What a difference grinding annealed steel !
 
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