Thinning my Blazen

[Brad Bellomo]

I have a heavily used Blazen originally 300mm but now 290mm. This might or might not be SPG2 as it has the pre-2008 logo. The edge has never been thinned, and which as pointed out on another thread, is long overdue. Two questions:

1) I probably want to buy a course stone for this. I am not exactly sure what I have, as I haven't used anything rougher than 4000 in a while, but I am certain they aren't flat. Rather than try to flatten an old stone, I'd rather buy new. Any recommendations? I also have a HAP40 68 HRC gyuto in the mail, so I might want to pick up a diamond, although at least the roughest won't see the new gyuto for a long time.

2) I am worried about over-thinning. This blade is prone to chipping. Is that a potential problem? Or is chipping only a concern changing the cutting edge angle? How do I know when I've removed the right amount of metal?

 

[Benuser]

The steel treated by Ryusen is not known for being specially chippy, once a first stone sharpening done.
The blade has become so thick that a lot of force is being used to get it through food, with a violent board contact as a result.
For thickness behind the edge you may use a thumb rule: above the edge 0.2mm, 5mm upwards 0.5mm, 5mm more 1mm. If it is the first thinning after years of sharpening only the edge while losing 10mm of lenght I would send it out. I'm used to thin my knives at every sharpening session, and thinning more heavily from time to time, and that's with simple monosteel carbons: I do have an idea of the amount of work that's involved in your case. The cladding is highly abrasion resistant, and something like 2/3 of the thickness has to be removed to have it work properly again. Don't even think about doing it yourself, by hand.

 

[Nemo]

Some pictures would probably help. It would be useful to see how big the edge bevel is and a choil shot would help too.

When recommending a stone, it also helps to know where you are located, as this affects how easy it is to get certain stones.

If it has indeed lost 10mm of length, I agree that it's probably a bit big for a first thinning job, especially on a convex ground non wide bevel knife. Power tools will make this job much easier but make sure it is done by someone who knows how to maintain the geometry of the blade and especially the temper of the steel.

If I need to remove a lot of metal (major thinning or major chip removal) I tend to use coarse wet and dry sandpaper on a sandpaper holder (I use the Kasfly). This gets around the main issue with coarse stones: they dish quickly and need frequent flattening. Flattening coarse stones will wear out your flattening hardware much faster. The downside is that you need to change the sandpaper frequently. The other user upside is that you can choose your own grit and it's very easy to make a tight sandpaper progression to get all of the coarse scratches out. I tend to switch to stones at either 320 grit (Suehiro cerax) or 600ish grit (Naniwa Chosera/ Pro 400).

If you do want to go down the very coarse stone route, there have been a few good threads on very coarse (under 300 grit) stones recently. Here is but one:

https://www.kitchenknifeforums.com/...suehiro-debado-180-200-or-shapton-220s.58043/
Others will reveal themselves with a Google search, I'm sure.

Some commonly recommend medium- coarse stones include Shapton Glass 500 and Naniwa Pro 400.

I tend to thin until the edge bevel is almost gone, just before you form a burr at your thinning angle (a so called zero grind). Even if it is VG10 rather than SG2, Ryusen does one of the best VG10 heat treats and it should be fine with a very thin geometry.

On that note, if it is VG10 this could explain your short lasting edge: VG10 is said to require meticulous deburring on every stone. I've never sharpened the stuff but @Benuser is an advocate for careful deburring of VG10 and he would likely be happy to share his experience with you.

Which stones (brand and line are important) are you using now? HAP40 is not that hard to grind on AlOx stones, even fine ones. But you will need to use a stone that doesn't load on high alloy steels.

If you want to use diamond on HAP40, you won't need it until you get to a medium or even a fine stone. The theoretcal issue (there is a bit of a debate about this, and indeed about the need for diamonds in these steels) is that a fine abrasive that is softer than the very hard W and V carbides will abrade the steel matrix but leave the carbides sitting proud. Or even worse, the carbides will be pulled out, leaving big craters in the edge. This seems not to be an issue with coarse abrasives, which seem to abrade hard carbides just fine. It's unclear whether fine abrasives also abrade hard carbides OK. FWIW, on high alloy steels I tend to use regular AlOx stones up to 1K and finish on 6k diamond and I think this gives me a shaprer result on these steels. One alternative is to sharpen at a higher angle (say 20 dps) or even use a microbevel with these steels. You could always combine a microbevel with deburring in the Kippington deburring technique, which is how I sharpened these steels before I had a fine diamond stone:

https://www.kitchenknifeforums.com/threads/kippington-deburring-video.44003/#post-651311

 

[Blank Blades.]

You certainly want to get some coarse stones for this. There isn't going to be anyway around that, especially with how thick this knife sounds at the moment..

Can you over thin? Technically yes, but I promise this isn't going to be a concern for you. I think you could probably thin down the primary bevel to zero, then put a koba (secondary bevel, or microbevel, whatever you want to call it). And you would get great performance.

Thinning can take a lot of work if you let the thickness get out of hand, so I really doubt you're going to overdo it.

As far as recommendations. Get a shapton 120 kuromaku (pro). Then something in the 400 grit range to get those scratches out, or you can use a sandpaper progression. Then a 1000 grit stone (I suggest at least buying a 1000 grit if you dont have one, and not doing sandpaper.) Then from 1000 you can move up to your 4000 stone (I'm assuming that wasn't a typo, and that you meant 400 instead) and on up.

I really suggest you dont start with anything finer than the 120 shapton. I personally would go coarser, but that is a middle ground stone that I think more people will recommend.


Regarding something @Nemo Said. it will certainly make the job much quicker using a belt sander, I might suggest not going that route if you want to maintain the original geometry of the knife. I'm not saying it's not possible, it's just not easy. But you can definitely just thin the knife down quickly if that's all that really matters, and keep the geometry similar enough to what it was originally.

I think just starting with a proper very coarse waterstone will get the job done with a reasonable enough amount of work. Plus it will be a good lesson on the importance of doing maintenance thinning

 

[Brad Bellomo]

I think the coursest I've ever owned was 800. Is a 120 kuromaku a $40 stone on Amazon? Do I need to do this all at once? Or can I take off a modest amount (and not go higher than 120) every time I sharpen until I decide not to go thinner? I don't want a zero bevel. Those scratches won't be great for things like sushi, but that isn't what this knife is used for.

 

[Nemo]

Yeah, you can do a partial thinning. When you see the improvement, you'll likely want do finish the job .

I sometimes do get to a zero grind when thinning (and always when doing a major chip repair). What you do then is to just put our usual edge on it (which will take zero minutes minutes on a zero grind) and you have a thin behind the edge knife with a durable edge.

You could refinish your thinning bevel with a wet and dry sandpaper progression. Start at whatever grit your coarse stone is and make jumps of 1.5ish fold. A hard curved backing makes it easier. I use a piece of pine that I have shaped the end of into a curve (with coarse sandpaper). When doing this, I usually blunten the edge (by GENTLY bread knifing on fine stone) for safety.

BTW, still waiting to see pics of the knife .

 

[Benuser]

Remember the soft cladding is like wood around the core of a pencil. It has get removed to free the core over time. You don't want the cladding steel to incorporate the edge.
Now, the soft stainless cladding is very abrasion resistant. This may seem strange, but it is both very though and abrasion resistant. Messy stuff to remove. A choil shot would help to find out how much has to be done. Measure the thickness at the shoulders — where bevel and face meet. A thickness of 0.2mm is reasonable for a knife with board contact.
Besides a 120 you would need another one to ease the scratches, probably in the 320 area, before you may finish it on a 800, and start normal sharpening. You want at least the bevel on the right side to form a continuous arc with the face — no shoulder.
All reasons to believe you better have it done by a competent sharpener with the right equipment and knowledge about Japanese knives and their geometry.
I'm a bit sceptical about partial thinning: as it has to be followed by a full sharpening, it is likely to provide only little improvement for a lot of work. A lot of the work is in restoring an acceptable finish. That's the same, whether you've removed a lot of cladding or just a little bit.

 

[Brad Bellomo]

Near when I first started, I bought two Norton stones - combination 220/1000 and 4000/8000. I've tried others (and stroops and paper), but almost always just use the 4000/8000 unless the knife is really bad.

I am in Ohio, USA.

My other concern with over-thinning is I am removing cladding but not core steel. Won't that eventually remove all the cladding?

I know this is personal preference, but I've never done this before. Do I want to remove material all the way up to the spine of the blade? Do I want to change this from a convex to flat grind?

My reason for partial thinning is to help me learn. If I make a huge change, I can completely ruin this knife. If I make a smaller change and see it is an improvement, I will do more next time (which could be 2 months or 2 hours). If I go this route, do I need to go beyond the coarsest stone?

 

[Nemo]

I'm a bit sceptical about partial thinning: as it has to be followed by a full sharpening, it is likely to provide only little improvement for a lot of work. A lot of the work is in restoring an acceptable finish. That's the same, whether you've removed a lot of cladding or just a little bit.

This is a really important point. The only time I've stopped before completing a thinning, I regretted it because of having to do the refinishing twice.

 

[Brad Bellomo]

If I start with a 120 kuromaku, is a Shapton glass 500 an appropriate next step?

 

[Benuser]

If I start with a 120 kuromaku, is a Shapton glass 500 an appropriate next step?

Yes, but if you have the choice, I would rather choose the SG320.

 

[Benuser]

"My other concern with over-thinning is I am removing cladding but not core steel. Won't that eventually remove all the cladding?"
That is exactly the purpose: you want the last part close to the edge to be free of cladding. Here with a discoloured carbon core and soft stainless cladding.

 

[Nemo]

Near when I first started, I bought two Norton stones - combination 220/1000 and 4000/8000. I've tried others (and stroops and paper), but almost always just use the 4000/8000 unless the knife is really bad.

I am in Ohio, USA.

My other concern with over-thinning is I am removing cladding but not core steel. Won't that eventually remove all the cladding?

I know this is personal preference, but I've never done this before. Do I want to remove material all the way up to the spine of the blade? Do I want to change this from a convex to flat grind?

My reason for partial thinning is to help me learn. If I make a huge change, I can completely ruin this knife. If I make a smaller change and see it is an improvement, I will do more next time (which could be 2 months or 2 hours). If I go this route, do I need to go beyond the coarsest stone?

Thinning is usually done at an angle of 2-5ish degree angle, so the majority of the cladding steel is removed near the edge. It creates a new wide bevel which usually goes a third to a half way up the blade face.

If there is a lot of metal to remove, you will need to focus on trying to maintain the blade face's geometry (convex in the lower half of the blade). Otherwise you will just be cutting a new flat wide bevel into the convex lower blade face.

This is why we want to see pics of the blade. If it's a minor job, we can give some guidance on how to proceed but if it is indeed a big job, I agree with @Benuser - it's not ideal as a first thinning job not only because of the size but also because maintaining the geometry becomes more important the more steel that needs to be removed. But we can't guess the degree of thinning required without seeing the blade.

 

[Brad Bellomo]

 

[Brad Bellomo]

 

[Brad Bellomo]

Would this be an appropriate progression?
120 kuromaku > SG320 > Norton 1000

This knife is not being sent out.

 

[Benuser]

Would this be an appropriate progression?
120 kuromaku > SG320 > Norton 1000

This knife is not being sent out.

My last attempt:
Photos of face and spine will hardly inform about thickness behind the edge.
You may at least explain why you exclude sending out.

 

[Brad Bellomo]

If you explain what you want to see better, I will try, but am skeptical it will help. The metal is between 0.4mm and 0.7mm. Even holding the knife in my hand, my eyes don't tell me anything.

This is my knife, my money, my stones, my decision, my hobby. If you are on this forum, I assume you enjoy knives, sharpening and cooking, otherwise why do you post here? Why do people cook instead of eating out?

 

[ModRQC]

If you send it out you'll get it back like new and then you could slowly learn maintenance thinning instead of going head first into major thinning.

Also, major thinning of soft SS clad over SG2 core (if it is) or even anything like VG-10 on stones is a harsh job. The more grinding you need to do, with little experience you have, the more "errors" you're likely to make.

 

[Brad Bellomo]

I have no problem leaving it in a drawer until I have more experience. I could also just buy a new Blazen 300mm if I really needed one. After 14 years, I'd rather retire it than have some stranger do a major reprofile.

 

[Brad Bellomo]

For slowly learn maintenance thinning, do I thin every time I sharpen?

The argument against partial thinning was it is a lot of the work is in restoring an acceptable finish. That's the same, whether you've removed a lot of cladding or just a little bit. If that's true, how does maintenance thinning make sense?

 

[tostadas]

If you explain what you want to see better, I will try, but am skeptical it will help. The metal is between 0.4mm and 0.7mm. Even holding the knife in my hand, my eyes don't tell me anything.

This is my knife, my money, my stones, my decision, my hobby. If you are on this forum, I assume you enjoy knives, sharpening and cooking, otherwise why do you post here? Why do people cook instead of eating out?

I totally understand. Opportunity to learn is worth it, so why not go for it. Just know that it will take a long time to do by hand, and the geometry likely won't be the best for your first go.

A helpful tool to have is a pair of calipers to check your progress often. I'd aim for 0.2mm @1mm, 0.6mm@5mm, 1.2mm@10mm behind the edge to start. To give you an idea of time doing it by hand, it takes me roughly 1hr to remove 0.1mm at 10mm behind the edge by hand, not including refinishing. Also keep in mind that you might want to finish a little thicker than final with your coarse at grits, because as you refine with higher grits, you will continue to remove some material.

For this much steel removal, I'd recommend sandpaper starting at 120 grit. Going lower in my experience does not really speed up the process and introduces deep scratches that take extra time to remove. 120-240-400, then test out the knife and see if it needs more. 400 grit finish from sandpaper is smooth enough that you can get a decent test without roughness of the blade coming into play.

Another thing to note is that sandpaper grits and Whetstone grits are not the same. The feel of finish on sandpaper to me seems about 3x higher than the same grit on stones, though cutting speed is much higher. What I mean is that 800 grit sandpaper feels like 2400 grit Whetstone finish.

If your knife is as thick as you describe, performance can only go up from there. So have fun and good luck.

 

[Justinv]

I tried thinning an old VG10 petty after like 10 years of abuse and a shapton pro 120 stone didn’t make a dent in an hour. It removed a gram of steel. I just polished it up and gave it away. It needed hours more work which wasn’t worth the effort.

 

[ModRQC]

A professional - not "some stranger" will probably charge about equal to buying one coarse stone to do the job, and you need more than one. He'll also refinish it nicely for you. Just saying, if you have knives enough to put this one in the drawer, you have material enough to learn thinning by doing more regular maintenance first.

I've nothing against your will to learn, but that's not learning what you're about to do. You'll grind and grind with no immediate results but scratches all over the place, not knowing at all what to expect, what to look for, with no notion of how much more you need to grind to even get somewhere.

 

[Brad Bellomo]

I totally understand. Opportunity to learn is worth it, so why not go for it. Just know that it will take a long time to do by hand, and the geometry likely won't be the best for your first go.

A helpful tool to have is a pair of calipers to check your progress often. I'd aim for 0.2mm @1mm, 0.6mm@5mm, 1.2mm@10mm behind the edge to start. To give you an idea of time doing it by hand, it takes me roughly 1hr to remove 0.1mm at 10mm behind the edge by hand, not including refinishing. Also keep in mind that you might want to finish a little thicker than final with your coarse at grits, because as you refine with higher grits, you will continue to remove some material.

For this much steel removal, I'd recommend sandpaper starting at 120 grit. Going lower in my experience does not really speed up the process and introduces deep scratches that take extra time to remove. 120-240-400, then test out the knife and see if it needs more. 400 grit finish from sandpaper is smooth enough that you can get a decent test without roughness of the blade coming into play.

Another thing to note is that sandpaper grits and Whetstone grits are not the same. The feel of finish on sandpaper to me seems about 3x higher than the same grit on stones, though cutting speed is much higher. What I mean is that 800 grit sandpaper feels like 2400 grit Whetstone finish.

If your knife is as thick as you describe, performance can only go up from there. So have fun and good luck.

Most people seem to recommend INDASA Redline Rhynowet, which is meant to be used wet, but they use it dry. It starts at 180 grit, but there is a 120 Rhynodry which to me looks more appropriate. Would you recommend either or something else?

 

[tostadas]

Most people seem to recommend INDASA Redline Rhynowet, which is meant to be used wet, but they use it dry. It starts at 180 grit, but there is a 120 Rhynodry which to me looks more appropriate. Would you recommend either or something else?

Rhynowet does goes down to 120 and lower. I've used both rhynowet and also 3m pro grade precision (the purple one from home depot) and can recommend both.

 

[JBroida]

for what its worth, before they were SG2, they used SG1... i have one of them... its still a very nice knife

 

[Brad Bellomo]

for what its worth, before they were SG2, they used SG1... i have one of them... its still a very nice knife

This makes more sense, as my ex-wife left with a Tojiro DP that was VG10. Very different feel both cutting and sharpening. Going by zknives, the composition of SG1 isn't that different from SG2.

 

[Nemo]

I have no problem leaving it in a drawer until I have more experience. I could also just buy a new Blazen 300mm if I really needed one. After 14 years, I'd rather retire it than have some stranger do a major reprofile.

We are definitely not looking at changing the profile. Just thinning the grind.

 

[Nemo]

For slowly learn maintenance thinning, do I thin every time I sharpen?

The argument against partial thinning was it is a lot of the work is in restoring an acceptable finish. That's the same, whether you've removed a lot of cladding or just a little bit. If that's true, how does maintenance thinning make sense?

Sure, but I do maintenance thinning whenever I drop down to a medium stone. I usually use a Chosera 1k which leaves a circa 1500 JIS scratch pattern. It's much much much easier to get Chosera 1k scratches out than to get coarse sandpaper scratches out.

Here is a thread detailing how I worked out a reasonable refinishing progression for a Blazen after a maintenance thinning:

https://www.kitchenknifeforums.com/threads/refinishing-a-ryusen-blazen.41707/page-1
A 1500-2000 +/- 2500 sandpaper progression works well and takes a couple of minutes per grit.

I guess that the main difference is that a medium stone finish is much closer to the finish you will want to put on the knife.