WARPING - Naniwa Gouken Kagayaki 10 mm , i.e. Super Stone

[sd_baker]

This has happened to me too - Naniwa Gouken Kagayaki 10 mm. Here is what I mean exactly by warping:

1. Flatten stone both sides. Verify flatness.
2. Dry off with towel and stand up on long side and allow to dry fully for 2 hours.
3. Verify flatness. There is now a noticeable bow on both ends of the stone, less than a mm, maybe 0.2-0.5 mm.

Verify flatness​

What I mean by this - I put a metal rule edge down on the expected flat surface and shine a bright light behind and check if any light passes. I verify the flatness of the metal rule on my kitchen counter and against my other flat stones. It is flat.

As a double OCD sanity check, I use a 1/2" cast acrylic block in a similar way (i.e. stand it up on its flat edge) as well.

Variations tried​

Drying on the side​

The warping is noticeable on both top and bottom surface.

Drying flat on one surface, laying on another flat stone​

The bottom side remains flat, while the top shows unevenness.

Other Threads​

Other threads I found :

• Naniwa 12k warp ? - https://www.badgerandblade.com/forum/threads/naniwa-12k-warp.626329
• Naniwa SS warp, other alternatives? - https://www.badgerandblade.com/forum/threads/naniwa-ss-warp-other-alternatives.644593

Conclusion​

I suspect based on all of this that this is not "warping", where both top and bottom surface move together, but rather uneven swelling and shrinking during drying. This makes me think that even if I glued to a flat substrate, the same swelling will be observed (see flat drying above).

I will not be able to return the product if I glue it, so there is no other choice but to choose a different company.

This is so so disappointing. I don't think I will be able to bring myself to buy a Naniwa product again.

 

[Herrenberg]

As you say, this is a known problem with the thinner superstones.

I wouldn't let it put you off of their other fine products, like Chosera and Hibiki and their excellent resin-bonded diamond stones.

 

[Gamma]

Warping is just a general term used to describe what happens when some Nani SS get wet and or dry out. Sort of an easy to use blanket term. There are a few dynamics in the mix of things, but the end result is a not flat stone, like a twisted 2x4 at Home Depot.
It's not just thinner stones, some of the thicker SS types suffer from this also.
I had a 20mm 12k SS that showed me every possible event over 2 years or so. Sometimes it would stay flat, other times only one side would warp, other times both sides warped and there was no rhyme or reason whether I dried it standing up on end. lying down on a flat surface, on the long side, on an angle, etc... nothing I did brought about any consistency in how it warped or the degree that it warped.
I've had more Nani stones without problems than with problems. But those that did have issues really ticked me off.

 

[sd_baker]

Update: 12 hours on and the stone is same as 2 hours on.

I went for this stone because Amazon has extended the return policy for now, and I just couldn't believe problems would be that common given who the market must be for 12k stones. I mean who's has need for 12k stones, but can be laissez faire about flatness?

I have shapton pros and never bothered to check flatness after use and flattening because they don't have this sort of careless reputation. After this SS incident, I went and checked my Shaptons. They are all flat.

I'm going to forego the paranoia and just avoid Naniwas where I can from now on.

 

[JPO]

I have a 8k Naniwa SS and a 12k in two pieces.
The 8k is glued to slate.
I just lapped it. It had a low spot in the middle. With my honing technique I usually end up with a high spot in the middle (rolling x-strokes).
I will let it dry a few hours to see if there is a new low spot after it has dried.
I personally don't think gluing these to something hard is a solution to the underlying issue with these stones. You get uneven stress in the stone as it dries. The middle will dry slower then the edges.
I will see what happens after a few hours.
I might also soak it a few minutes if it is not flat just to see if it stabilizes.

 

[Tanuki]

The current Superstones are not soakers. Instructions are splash and go. From Naniwa, I only have S2s and a single Chosera. No warping issues in a few years of use. I just bought a 2k and 10k, to fill in the sequence and play with absolute minimum jumps in grit from 1k to 12k. Holiday discount pricing got me.

My Chosera 600 also seems bulletproof.

Mine are stored on edge in the drying rack, covered with a dry towel. I hone (usually only one or two razors in a session) with a splash of water and a tiny spritz of Keen Kutter. I flatten using a Dia-flat under running water.

 

[JPO]

I know these are considered splash and go. However, a short soak can help to stabilize the resin, and provide a slightly better feedback.
Which instructions are you referring to?
A short soaking is at least recommended on Ninwa's home page.

 

[JPO]

After 4 hours of drying the slate backed 8k is now lapped again. The stone went from being flat to convex.

It is now going to try properly to tomorrow morning, just to see if there is a difference.

Now I am starting to remember why I stopped using these stones.

 

[sd_baker]

New experiment: soak in warm water for 5 minutes.

Result: no change, still as uneven as before.

I'm going to dry overnight and see.

 

[sd_baker]

After 4 hours of drying the slate backed 8k is now lapped again.

Lapping is your way of looking for unevenness?

 

[JPO]

Lapping is your way of looking for unevenness?

I check with a straight edge first, then i apply grid marks on the stone,
and lap off the grid marks.

 

[Mr Kooby Shemayrew]

Lapping is your way of looking for unevenness?

I have the Naniwa Fuji 4K and Falcon 8K. When they were new the surfaces would seem to grow overnight after each use. This required lapping and flattening them before use each time. This effect has gone away and they stay flat now. I guess it took about 15 or so times using them.

Hopefully what you are experiencing is just a temporary phase until the stone settles from being new and going through X-number of wetting and drying cycles.

 

[sd_baker]

Here is another experiment I could try, if I had a few years to wait...

I left a Naniwa 12K in a bucket of water overnight.
I know I wasn't supposed to do that.
It warped and I let it dry as much as it would, and I put it away for a few years.
I just looked at it recently and it is completely flat.

 

[Herrenberg]

Clearly the key to the SS 12K is to leave it alone and not use it. I can proudly say that I have wisely done that with mine.

 

[sd_baker]

The irony here is I was considering the Proyan Glass 15k as a finishing stone, then I said to myself "don't waste time on inferior products, go for the stone everyone recommends as the starter synth finisher".

 

[JPO]

After the stone has dried over night I can see that it is now slightly convex again.
However, it did not take many laps with a 600 Atoma plate to get it flat again.
This is something I do with every synthetic stone before use anyway. I don't do it just to make them flat.

So, in my opinion gluing the stone doesn't completely eliminate the swelling issues. However, I don't have to threat this any different then any of my other synthetic stones.
This is not a new stone, so it should have gone through enough drying sycles.
I never got along with my superstones. Warping and swelling was not one of the reasons.
However, the 12k is probably one of the best finishing stones in that price range. So, get the extra thick versions or glue the standard version to something stable.

 

[Gamma]

I've owned 4-5 12k Nani Super Stones. One was a 10mm, the others were the thicker type, 20mm or so.
The only one that warped was the last one, which was 20mm thick. I've borrowed a couple along the way and they were fine also.

In my case, and othbers that I have discussed this with, the warping, twisting, swelling, was unpredictable and not fixable and it was always so far out of flat that lapping it back to flat took a very long time. That stone also had a crusty surface initially, with a lot of shallow pockmarks that were not visible until they were magnified.
One of the earlier 20mm 12k stones I owned had a similar top surface, but did not warp. I had to lap a lot off that stone before it behaved correctly though.

So maybe someone buys one and gets a good one. Or it just warps a little, or maybe it warps so bad that it's not acceptable to the user. How many people own Super Stones that are warping but they don't realize because they think lapping off grids means the stone is flat? Grids can come off a SS very quickly, way long before it's actually flat. Then someone might say if they don't notice does it really matter?
What matters to me, is that the stone I bought works as I need it to, not how it fells like based on humidity, hydration, cycle of the moon, etc If gluing the slab to granite is the fix, or a partial fix, keep it... no bueno. This stuff isn't cheap and it should not be doing gymnastics when I'm not around. Plus, maybe gluing it down might cause the internal stresses to crack the stone eventually. Seems possible.

So, at the end of the day, buying them is a gamble. The odds of getting a good one are probably in one's favor but the chances of getting stuck are there.

I had a full set of 10mm SS, and two sets of 20mm SS, plus a decent number of individual SSs, duplicates, etc along the way. Only one was a warper. I had a higher ratio of crazing Choseras.

 

[Steve56]

All of this has been discussed many times, but my philosophy is to lap after honing. IOW, you lap the stone in the same hydration state that you hone. If it warps when it’s dry, so what? Give it a 10m soak to simulate honing a razor on it and check the flatness. If it isn’t flat try soaking it another 10m. If it still isn’t flat enough for you get a ceramic stone, not a resin stone. Use the resin stones for knives.

I’ve never worried about absolute stone flatness, that’s a rabbit hole all by itself. Your stone needs to be as flat as your razor spine is straight and of even thickness heel to toe, and as flat as your edge is straight. If we’re talking vintage razors, that’s not many of them.

If you’re honing plane irons for kezurokai competition, then yes, you need to worry about how flat your finisher is, vintage razors, not so much.

 

[sd_baker]

If it still isn’t flat enough for you get a ceramic stone, not a resin stone. Use the resin stones for knives.

Do all resin stones do this? What are other resin bonded stones? When I google "resin sharpening stone", all I get are the diamond resin ones.

I was also considering the Kouseki 10k, which is magnesium bonded, I believe.

 

[Steve56]

Do all resin stones do this? What are other resin bonded stones? When I google "resin sharpening stone", all I get are the diamond resin ones.

I was also considering the Kouseki 10k, which is magnesium bonded, I believe.

I have no idea except that people complain about Naniwa Super Stones/Traditional, maybe because they aren’t currently fashionable. And the Chosera/Pro for cracking at >1k grits. I I have no issues with Naniwa Super Stones/Traditional.

In general, use more modern stones, if for no reason than they cut hard, modern steels. That’s where the knife and razor steel arrow is pointing.

The Suehiro Kouseku 10k is a winner IMO, I’m currently using it a lot, then to a JNat, but it can finish a razor very well by itself.