How do you grind kitchen knife blades (stock removal) ?
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A few more blades ground down the road and the first that was also ground (smaller adjustments to the grind) after HT. It is a D2 gyuto. I am having a lot of trouble removing scratches on a belt grinder (the 1x30"). I have ground the blade with Sait 7S grit 40 belt, did the work I needed to be done. Then I have moved to 80, 120 and 240 belts (all Sait 7S) trying to remove scratches form the previous belt (not easy to observe as all are going in the same direction). I was not happy already during the grinding as I was often getting the impression that I can not 'reach' certain places on the blade - like I would have low spots roughly in the middle between edge and spine. Once I have moved to hand sanding I had to go down to 80 grit paper and still needed 1/2 hour to remove scratches left by the grinding.
I am wondering what was the reason. On one hand - the 'platen' the grinder has is some 3mm thick L-shaped piece of metal that is only attached to the grinder on one end, so it can give under pressure. On the other hand I am having hard tome to estimate when I have removed the scratches from the previous step as I can not really grind under different angle with every step as that just seems hard to do on a belt grinder + there is not enough place on this little one.
I would appreciate your thoughts.
This is the grinder in question - here you can see the 'platen'. I remove the 'work rest' for bevel grinding though:
I am wondering what was the reason. On one hand - the 'platen' the grinder has is some 3mm thick L-shaped piece of metal that is only attached to the grinder on one end, so it can give under pressure. On the other hand I am having hard tome to estimate when I have removed the scratches from the previous step as I can not really grind under different angle with every step as that just seems hard to do on a belt grinder + there is not enough place on this little one.
I would appreciate your thoughts.
This is the grinder in question - here you can see the 'platen'. I remove the 'work rest' for bevel grinding though:
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Well for what it is worth, when I took a lesson with WillC he often used a push stick to apply pressure to the part of the bevel that he wanted to grind more of...
A few more blades ground down the road and the first that was also ground (smaller adjustments to the grind) after HT. It is a D2 gyuto. I am having a lot of trouble removing scratches on a belt grinder (the 1x30"). I have ground the blade with Sait 7S grit 40 belt, did the work I needed to be done. Then I have moved to 80, 120 and 240 belts (all Sait 7S) trying to remove scratches form the previous belt (not easy to observe as all are going in the same direction). I was not happy already during the grinding as I was often getting the impression that I can not 'reach' certain places on the blade - like I would have low spots roughly in the middle between edge and spine. Once I have moved to hand sanding I had to go down to 80 grit paper and still needed 1/2 hour to remove scratches left by the grinding.
I am wondering what was the reason. On one hand - the 'platen' the grinder has is some 3mm thick L-shaped piece of metal that is only attached to the grinder on one end, so it can give under pressure. On the other hand I am having hard tome to estimate when I have removed the scratches from the previous step as I can not really grind under different angle with every step as that just seems hard to do on a belt grinder + there is not enough place on this little one.
I would appreciate your thoughts.
This is the grinder in question - here you can see the 'platen'. I remove the 'work rest' for bevel grinding though:
There are several factors that are working against you with your a 1x30. Since you only have a 1" wide platen, you have a greater chance of introducing the blade onto the platen at an angle and not perfectly flat to the platen. This creates deeper scratches as the blade is going across the edge of the platen. I'm not sure how stable your platen is, or if it has a ceramic glass backing, but lack of stability can cause problems as well. Another big disadvantage you have with the 1x30 is no ability to vary the speed of the belt. Fast is great for removing lots of metal, but a slower speed gives you much more control when working out scratches.
Something I do to find those deep scratches before going to the next belt, is to take the blade to my vise, using a sanding block and the same grit paper as the last belt I used, I sand the blade length ways (opposite of the belt marks). It won't take long doing this for the high and low spots as well as the deep scratches to show up.
I'm pretty sure a variable speed 2x72 machine and lots of grinding practice would be the cure to your problems.
Hope this helps!
Thank you. Those are all good points. I did have one intermittent loop when after 80 (or 120) belt I went to hand sandig with 80 grit paper and since I was not seeing progress after a while - I went back to the belt sander and even with 40 grit belt I had a really hard time to get those 80 grit scratches from hand sending removed from some parts of the blade.
Yes, the platen is rather flimsy and probably in the core of the problem.
2x72" grinder is in serious planning phase - if everything goes as hoped, I could have one by the end of the year.
Yes, the platen is rather flimsy and probably in the core of the problem.
2x72" grinder is in serious planning phase - if everything goes as hoped, I could have one by the end of the year.
Kippington
A small green parrot
Oh man I didn't realize until I watched those videos just how different stock removal is from grinding a forged blade.
There's no way to scribe the center of a forged blank, its way too irregular, so instead of starting at the edge I have to start from the spine and grind my way to the edge from there.
Deep hammer marks are the biggest pain in the ass for me to deal with at the grinding stage and I quickly learned to hit accurately while forging. It only takes one bad swing with the hammer on a hot blade and the corner of the hammer leaves a big ol' imprint on the blade surface that adds another half-hour of grinding to the project.
I can't imagine how long it would take to grind hardened steel like some of you guys do. I use a weak/cheap 1x30 belt so perhaps it's easier with a proper bladesmith grinder. I have to anneal my blanks after forging to keep the metal soft enough for my grinder, which comes with the added benefit of being able to bend a crooked edge straight. This kind of makes up for the lack of center marking that you would do on a stock removal edge.
Interesting thread!
Checking a 40 grit finish for irregularities. Next I'm gonna cut out the choil then prepare for a clay-coat marquench.
There's no way to scribe the center of a forged blank, its way too irregular, so instead of starting at the edge I have to start from the spine and grind my way to the edge from there.
Deep hammer marks are the biggest pain in the ass for me to deal with at the grinding stage and I quickly learned to hit accurately while forging. It only takes one bad swing with the hammer on a hot blade and the corner of the hammer leaves a big ol' imprint on the blade surface that adds another half-hour of grinding to the project.
I can't imagine how long it would take to grind hardened steel like some of you guys do. I use a weak/cheap 1x30 belt so perhaps it's easier with a proper bladesmith grinder. I have to anneal my blanks after forging to keep the metal soft enough for my grinder, which comes with the added benefit of being able to bend a crooked edge straight. This kind of makes up for the lack of center marking that you would do on a stock removal edge.
Interesting thread!
Checking a 40 grit finish for irregularities. Next I'm gonna cut out the choil then prepare for a clay-coat marquench.
Indeed - I find grinding blanks made out of stock steel demanding enough. Grinding bevels on dorged blade is entirely different level. Since you are also using a small 1x30" grinder I would appreciate any tips or trickes how to get most out of it.
I agree that grinding the blanks from stock after HT would take forever with this little weak grinder.
On the topic of scratches on the D2 knife I am working on at the moment. Obviously large part of the 'problem' is the steel itselt. It is VERY wear resistent. I have already spent nearly 3 hours going from 80 to 400 grit and I am not finished yet. The work with the 80 was so tough, that I went with sanding parallel to the knife axis just to be able to put more pressure into it without risking damaging the edge. I am NOT lookimg forward to the other side.
I have a batch of O1 knives in process (still grinding prior to HT). I will not be going back to D2 anytime soom (at least not for large kitchen knives). I do plan to try stainless, but it will be AEB-L and Niolox. I will probably stay with O1 as my main carbon steel for the foreseeable future.
I agree that grinding the blanks from stock after HT would take forever with this little weak grinder.
On the topic of scratches on the D2 knife I am working on at the moment. Obviously large part of the 'problem' is the steel itselt. It is VERY wear resistent. I have already spent nearly 3 hours going from 80 to 400 grit and I am not finished yet. The work with the 80 was so tough, that I went with sanding parallel to the knife axis just to be able to put more pressure into it without risking damaging the edge. I am NOT lookimg forward to the other side.
I have a batch of O1 knives in process (still grinding prior to HT). I will not be going back to D2 anytime soom (at least not for large kitchen knives). I do plan to try stainless, but it will be AEB-L and Niolox. I will probably stay with O1 as my main carbon steel for the foreseeable future.
Kippington
A small green parrot
How to get the most out of a 1x30"? Seeing it's not as fast or powerful as some of the other grinders out there, use the coarsest grit you can find and expect it to take a longer time. It's not a bad thing for a beginner!
The process is slowed down enough that I can grab a beer, wear my earphones under my hearing protection and chill out to music while taking my sweet time at the grinder trying to get things right. Its not like I'm making a product for a waiting customer; I can stop and resume whenever I want.
Use time to your advantage and get everything right. The blade above took maybe 5 hours over 2 days to get to that state from forged blank. It still needs a few hours work, but I have to heat treat it before it gets too thin (edge is 2mm).
Polish a blade from scratch once and you'll never forget the simple rule - Each polishing stage depends on the last, all the way up from the rough shaping.
What tools are you using to do the hand sanding? Maybe your flat backing behind the sandpaper is bending as you put pressure on both ends, leaving an arch above the middle of the blade.
If you think you have a low spot you can check with a flat object and a back-light. It's a very quick test you can also do while coarse grinding.
A slightly convex blade face is the easiest one to polish (and makes for a good kitchen knife!).
Chuck also had some good advice about the scratches.
The process is slowed down enough that I can grab a beer, wear my earphones under my hearing protection and chill out to music while taking my sweet time at the grinder trying to get things right. Its not like I'm making a product for a waiting customer; I can stop and resume whenever I want.
Use time to your advantage and get everything right. The blade above took maybe 5 hours over 2 days to get to that state from forged blank. It still needs a few hours work, but I have to heat treat it before it gets too thin (edge is 2mm).
Polish a blade from scratch once and you'll never forget the simple rule - Each polishing stage depends on the last, all the way up from the rough shaping.
What tools are you using to do the hand sanding? Maybe your flat backing behind the sandpaper is bending as you put pressure on both ends, leaving an arch above the middle of the blade.
If you think you have a low spot you can check with a flat object and a back-light. It's a very quick test you can also do while coarse grinding.
A slightly convex blade face is the easiest one to polish (and makes for a good kitchen knife!).
Chuck also had some good advice about the scratches.
All good points. I agree that trying to hurry is a recipe for a poor result. Most of knives I grind do indeed have a convex grind (flat grind on a tall kitchen knife would not make for too impressive performance anyhow). Yes - the support I use for hand sanding is a piece of simple hard wood with a cross section of 10x30mm, so it most probably bends a little. But I do not really have problem with hand sanding (it just takes very long in the case of the D2 steel), but when sanding with the grinder where the semi-stiff platen is probably not an advantage.
I really like your 'checking screen' - reflecting a pattern onto the blade is indeed a great idea to see local disturbances to the surface. I will try to make something similar. I am using similar technique to check for the shape of the grind as you show above. It also allows to spot some left-right asymmetries.
I really like your 'checking screen' - reflecting a pattern onto the blade is indeed a great idea to see local disturbances to the surface. I will try to make something similar. I am using similar technique to check for the shape of the grind as you show above. It also allows to spot some left-right asymmetries.
In a general sense, I use a work rest tilted to the bevel angle and hold in a fixture, on a flat platen, post heat treated. I am currently working on a 8" Gyuto that will require a large work rest.
I do not yet have the skills to grind a knife of that length freehand. I find with this method, I have very little scrap.
I do not yet have the skills to grind a knife of that length freehand. I find with this method, I have very little scrap.
