Shapton 12k seems coarser than the 5k

[KennyB]

I just got a 5k and 12k of the Shapton Ha No Kuromaku, and it seems like the 12k is actually coarser than the 5k, both in terms of the feel while honing, as well as the finish it leaves.

When I first got them, I didn't think they felt very fine, but I had no basis of comparison since I've only ever used pretty coarse hones. I decided to sharpen my D2 OKC Rat II on them. When I finished on the 5k, it had more of a matte finish, and when I proceeded to the 12k, it left kind of a hazy mirror polish. I couldn't get it to whittle hair off the 12k, but just chalked this down to it being a new stone I wasn't used to.

I didn't really expect to get a mirror polish, but what I found weird was that the 12k felt super aggressive. Even with super light pressure, it felt like it was cutting metal off the Rat II very readily, and I couldn't get it as sharp as I normally could. For comparison, I usually finish the Rat II on a DMT 600 grit to a hair whittling level. My DMT hone has been broken in over many years, but the 12k still felt even more aggressive.

I didn't get anything like a diamond plate to lap the Shaptons on because I read on their site you could just rub the two stones together, so that's what I did. I noticed after doing so that the surfaces felt much more smooth and fine, and more like what I would have expected such high grit hones to feel like, and figured that must have solved the problem.

So I decided to hone my cheap Gold Dollar straight razor on them at that point, and this time the 5k left a very nice mirror finish. However, as soon as I moved past it to the 12k, it once again felt super aggressive and I noticed it had left lots of scratches in the mirror finish the 5k had left.

I was very careful to clean the blade and my hands after moving from the 5k to the 12k, so I don't think it's from carrying the 5k grit over to the 12k surface like Shapton suggests in their FAQs. Maybe I contaminated the 12k surface with the 5k grit by rubbing them together? But that still wouldn't seem to account for why the 12k feels so much coarser.

I saw someone suggest that using too much pressure on the 12k would make it feel too aggressive and leave scratches, so I tried using very faint pressure, but it still felt like it was much coarser than the 5k and once again put scratches into the mirror finish left by the 5k. I'm not trying to say my technique is perfect, but I do know how to use extremely light pressure and my 600 grit DMT to get hair whittling edges; still even the lightest I could hone against this 12k, it felt much coarser than the 5k.

I was starting to worry maybe there was some kind of quality control issue and read some reviews on Amazon and noticed another reviewer seemed to have the exact same experience. I'm not discounting the possibility that both of us are using it wrong, but that does make me worried we both could have got lemons too.

So I decided to try the OKC again on the 5k instead of the 12k and it was much easier to get an edge that whittled hair off of the 5k than the 12k. I mean honestly it was like a night and day difference.

Anyway, sorry to blab that much but I just wanted to give enough detail. At this point I'm wondering if this is just the way the 12k is supposed to feel and perform or if I should try to exchange it for another one. It's really hard to believe that this is normal, but since these are my first hones of this grit level it's really hard for me to say.

 

[Craig James]

Never used either as I like the chosera range, but sounds like you have a dodgy / fake stone there...

 

[rm41400]

I have the shapton 12 k and it definitely leaves a nice mirror finish on a chisel back.

It’s noticeably finer than the 8k Shapton Pro.

I rub these two together all the time and have no contamination issue.

something sounds off... I’m very happy with my 2k,8k and 12k

 

[Ourorboros]

I have had both, the 12K definitely leaves a finer edge on steels that are suitable for it.
However D2 is known to have large carbides - many people only sharpen to mid-grit and strop. Perhaps we are looking at carbide pullout here, which will leave a ragged edge.

 

[KennyB]

I think what happened is that I am just used to using very soft waterstones. When I flatten my Norton 220/1K on a piece of sandpaper, the 1000 side ends up feeling a lot rougher than it should, and leaves a coarser edge, but only for a little bit, and as I continue to grind on it, it smooths back out within a few dozen strokes.

I think the same thing happened here because eventually I was able to get a good mirror polish on the D2 knife that I had, much better than yesterday. As well as that, the 5K hone stopped leaving as polished of a surface. So what I think what happened was that the 5K got left smoother than it should have been, and the 12K rougher than it should have been, and both just needed a lot more grinding done on them before it broke into the hone's abrasives beneath the burnished surface grit.

I actually did a ZDP-189 edge on the 5K and 12K before trying the D2 again, and I think this made the difference because it was so much harder than both the D2 and surely whatever 1070-series carbon the cheap Gold Dollar was using.

So at least I know the hone isn't defective, but I'm still not sure I really like this, because it took a lot of sharpening to abrade the roughed-up surface and get to the grit underneath of where it was burnished. They seem like they will stay flat through many more sharpening than my Norton, but I was planning on lapping/flattening them every time to keep them flat all the time. However, if I do that, it's clear they're going to need a lot of grinding done on them before whatever surface the flattening abrasive leaves on them departs.

I've read around and it seems like the best option would be to get a flattening plate and some SiC powder and try to match the grit of the hones as close as possible. That way I'm flattening, but not burnishing the surface to a smoother/rougher feel than the abrasive beneath.