Avoiding scratches with hard Tomo Nagura

[Slish Fish]

Hi all, I've noticed a tendency with very hard tomo nagura to dislodge some larger abrasive grains that can scratch the base stone or a razor bevel. I just cut a hard Nakayama Kiita into tomo nagura today that it is very prone to this, even with a very fine surface finish and all the edges carefully broken. I have never run into this problem with Mikawa nagura or any other softer stone (tsushima, akapin etc). Has anyone else here run into this issue and maybe come up with a solution?

A photo of the two tomo nagura in question. The scratches on the stone underneath are from the nagura:

 

[rhgg2]

Another VIC jnat person?

Lapping a bit of a curve into the tomo works well. I can recommend this video:

Less pressure and patience. Finishing it finer may not help because if it's too fine it will just burnish and then slurry even slower. I finish the stone to 400 and the nagura to 200 or 400. I still scratch things up badly from time to time, then there's nothing for it but to wash the stone clean and start again. But just practicing again and again seems to reduce the incidences, there's definitely a knack.

 

[Slish Fish]

Another VIC jnat person?

Lapping a bit of a curve into the tomo works well. I can recommend this video:

Less pressure and patience. Finishing it finer may not help because if it's too fine it will just burnish and then slurry even slower. I finish the stone to 400 and the nagura to 200 or 400. I still scratch things up badly from time to time, then there's nothing for it but to wash the stone clean and start again. But just practicing again and again seems to reduce the incidences, there's definitely a knack.

There's a few of us! I do ultimately round off of my nagura just to avoid the vaccum suction effect onto the base stone but I try to achieve this during use rather than 'wasting' nagura by grinding it off on a diamond plate. I've rounded off the most problematic nagura and it's feeling a lot better! Thank you - and thanks for the video link, I've always felt a bit like I've been doing the wrong thing by rounding off my nagura faces so I'm feeling quite vindicated.

I'll give the rounded off nagura a try tomorrow morning and see how honing sounds and how the edge looks under a bit of daylight.

 

[Steve56]

Are you letting the nagura tip during use? If you let it tip, it will scratch the stone even if the corners/edges are rounded.

Try de-glazing both stones with a worn diamond plate and just using normal pressure so the nagura doesn’t tip.

 

[H Brad Boonshaft]

Yes, I round the corners, not just chamfer, on my tomo much more, especially at the ends and remove all sharp corners. Yours look more beveled, that will leave a sharp edge and corners that can chip easily.

It can seem a waste but a truly hard tomo will not wear out in our lifetime, you should not need that much slurry with a hard stone to finish.

I prefer a harder base stone for finishing with just a hint of diamond slurry.

Alex Gilmore has a good videos on his old site, TheJapanStone, on shaping nagura.

 

[psfred]

Those are pretty big for nagura, I suspect one of the reasons they are typically smaller is that you get less suction to the base stone, hence less tendency for the edge to dig in.

The few I have are small nagura with non-rectangular shapes and they are slightly rounded with a large radius at the "corners".

 

[Matt O]

I love big nagura and think those look sweet!

It’s like anything else in life…

experimentation + practice + persistence = perfection

You’ll figure it out, just don’t give up…and don’t forget a worn 1200 Atoma makes an awesome “Tomo Nagura!”

 

[Steve56]

I never rounded the end of naguras. All that does is reduce the contact area with the stone, so for the same amount of force on the nagura, the pounds per square inch is much higher because there is less nagura area in contact with the stone. Iwasaki recommends to not use high pressure, and to use lower pressure longer, which is what most of us are trying to avoid.

There’s a better way though, and that’s keeping your stone and/or nagura deglazed. I usually use a well worn Atoma 600 and since it’s out, I use it on the nagura too.

Originally posted in the wrong thread, apologies.

 

[Slish Fish]

I rounded off one of the nagura then roughed up the surface a bit with a fresh atoma and went about creating slurry really, really gently. Unfortunately, I still heard some pretty crunchy sounds on that first stone and definitely felt a bit of scratchiness underneath a knife and a razor. So, I tried moving to a harder base stone - success(ish)! On a very hard stone with very light pressure I can make smooth slurry without any crunchy sounds popping up:

However, the base stone is one of those stupid-hard Nakayamas that take a million years to work one's head around - still yet to fall in love with this one. I did find a generally good level of polish off of this slurry but plagued by small scratches (the photo is from one of those cheap USB microscopes but it's enough to get the idea). I was really careful to leave a nice pre-finish so I am certain these scratches are from the last stone. You can also see a nice little nick in the edge - that was from previous attempts at honing with chunky nagura slurry on the first stone.

I'll keep attacking the problem this weekend and update if I have any breakthroughs - maybe this kiita is just too dang hard, we'll see! Hopefully I haven't cut a decent hone in half for nothing! Thanks for all the advice everyone, I'll post a couple of pics of the base stones below for anyone interested - the mizu asagi is hard and fine and the asagi is very, very hard and fine but like every super-hard Nakayama I've tried can be scratchy when used with pressure. Both have remnants of what look to be Maruka stamps. I've got no clue on the authenticity, though the mizu asagi looks pretty legit. With how often these stamps are faked there's just no knowing. I've taken a photo next to a genuine Maruka stamp from a (top) for comparison.

Happy honing everyone!

 

[alex1921]

I love big nagura and think those look sweet!

It’s like anything else in life…

experimentation + practice + persistence = perfection

You’ll figure it out, just don’t give up…and don’t forget a worn 1200 Atoma makes an awesome “Tomo Nagura!”

Exactly. I will frequently take a koppa, round off one of the short sides and use it as a tomo. Endless possibilities.

 

[Gamma]

What makes a Tomo a Tomo is how it performs as a Tomo.
Not all stone makes good Tomos. Not all stones like all Tomo.

Don't press hard.
Go slow. Let the stone do the work.
Curve the working surface of the Tomo. Work with the curve, not against it.
Nagura can be softened a bit with water, prior to use. Just tonight I soaked Mejiro, Koma, Tomo.

If scratches in the base stone can be felt, that's one thing and not good.
If scratches are seen but not felt, that's something else and usually not an issue.
These stones contain abrasive silica, it's not like wiping butter on a hot skillet.

 

[DrVK]

less pressure and selecting the right tomo for base stone. trying/forcing to make something to work is never a good idea.

what is the base stone like without tomo? have you maxed it out?

 

[Yuan]

I rounded off one of the nagura then roughed up the surface a bit with a fresh atoma and went about creating slurry really, really gently. Unfortunately, I still heard some pretty crunchy sounds on that first stone and definitely felt a bit of scratchiness underneath a knife and a razor. So, I tried moving to a harder base stone - success(ish)! On a very hard stone with very light pressure I can make smooth slurry without any crunchy sounds popping up:
View attachment 1937003

However, the base stone is one of those stupid-hard Nakayamas that take a million years to work one's head around - still yet to fall in love with this one. I did find a generally good level of polish off of this slurry but plagued by small scratches (the photo is from one of those cheap USB microscopes but it's enough to get the idea). I was really careful to leave a nice pre-finish so I am certain these scratches are from the last stone. You can also see a nice little nick in the edge - that was from previous attempts at honing with chunky nagura slurry on the first stone.
View attachment 1937004

I'll keep attacking the problem this weekend and update if I have any breakthroughs - maybe this kiita is just too dang hard, we'll see! Hopefully I haven't cut a decent hone in half for nothing! Thanks for all the advice everyone, I'll post a couple of pics of the base stones below for anyone interested - the mizu asagi is hard and fine and the asagi is very, very hard and fine but like every super-hard Nakayama I've tried can be scratchy when used with pressure. Both have remnants of what look to be Maruka stamps. I've got no clue on the authenticity, though the mizu asagi looks pretty legit. With how often these stamps are faked there's just no knowing. I've taken a photo next to a genuine Maruka stamp from a (top) for comparison.

View attachment 1937005

View attachment 1937006

Happy honing everyone!

That is some nice looking stones. Don't see stones like that these days. I have been looking to scratch that maruka itch. One day I'll get my chunk. I hope!

 

[Slish Fish]

less pressure and selecting the right tomo for base stone. trying/forcing to make something to work is never a good idea.

what is the base stone like without tomo? have you maxed it out?

I've found these tomo work alright on another piece of Nakayama Kiita that I have. Never ended up getting them to co-operate with the harder base stones. I've had better luck using a couple of softer pieces of asagi for tomo that I have lying around which seem to be much more fit for purpose.

I think it's a case of needing a really precise match up of tomo and base stone - these nagura just don't play nice with anything but kiita that I've tried.

 

[GreazyThumbs]

Sometimes if they are very hard I will let them soak in water while I am going through the rest of my progression, this helps to tame some tomo's even if ever so slightly