Thread: Naniwa Bulge

The photo below is of a Naniwa 10k that has been lapped for just a few seconds with a DMT plate. What causes this bulge in the middle (that the DMT is shearing off)? I have lapped this stone before so after some honing use shouldn't it tend to show wear in the midle instead of a bulge?

Very interesting. I suppose it's possible that
the hone is reacting to temperature, moisture,
or water absorption, but that seems a bit far-
fetched.

I don't see this pattern on the stones that I lap
(which don't include a Naniwa)...

- Scott

That's bizzare. You say, you lapped already, used it once, or so, and now there's a bulge in it.
I just bought a Naniwa 12k myself, I lapped it with my DMT D8XX, then D8C, then 220, 320, 400, 600, 800, and 1000 grit sandpaper. The surface came out great. I've used it once on a real problem blade as the final hone so I really can't judge it on that alone. You aren't excessively submerging it, or really soaking it in water are you. They're quite soft, and porous.
Anyway, The hone really shouldn't wear at all after just a little honing, You mean like one razor? It would take some time for it to wallow out. If I were you, I'd contact the seller and let them know. Your sure it was lapped flat the first time you did it.
Did you check it with a straight edge...

Is it your first time lapping the naniwa ? Not unusual IME to have a new hone need a good flattening the first time around. I have no experience with naniwa though.

Edit; Duh, just re-read the post and I see you lapped it before. I have to lap the shapton pros every time and usually they are concave rather then convex. Maybe the binder in the naniwa is polymer like the shaptons and tends to move over time.

I've lapped it and honed razors on it several times. Based on the amount of use I would have expected only a small bit hollowing in the middle.

Oddly it has shown this bulge pattern before when being lapped. I assumed (as you suggest) that it had something to do with wetting and drying. In the future I may try lapping it dry instead of under running water. (I spritz it when honing rather than soaking it.)

This Naniwa 10K Superstone is 3/4 inches thick rather than 3/8 like those at SRD, so that may accentuate any such tendencies.

One other thing you might check, see if any other stones you lap with your DMT have a similar profile. I had to send a 325 back to them for replacement. It wasn't flat and left the stones wallowed out slightly with a gradual curve toward the center from each end.

Is it porous? Maybe the water in the middle of the stone is taking longer to dry out and is causing the edges to shrink while the middle stays raised?

I think that the size of what you use to lap the stone makes a diference. If the stone is around the same size as the lapping surface, there's a tendency to overshoot the lapping plate on each stroke and at each end. At first I thought that this would result in the middle being hollowed-out, but found that the middle was raised. I suspect the andle of lapping or the pressure used changes on the overhang. Lapping a 1000 grit on a DMT about the same size as the hone first showed up the problem for me, as this hone laps very quickly. Changing the DMT for a large sheet of sandpaper laid on a flat glass plate removed the bulge in the middle of the hone. The hone never went past the edge of the paper. Maybe it's also the pressure I was using at the time - I know that you should just let the stone work under its own weight or thereabouts, but always being in a hurry I probably "assisted" too much! Maybe something like this has happened to you?

Regards,
Neil

Originally Posted by crazycliff200843

Is it porous? Maybe the water in the middle of the stone is taking longer to dry out and is causing the edges to shrink while the middle stays raised?

+1 on that.

Bart.

These stones are porous, as I said earlier. Other than that, Neil pointed out about being inconsistant on the DMT's which is easy. It's always a good idea to finish on some Wet/Dry Sandpaper. Start with your 220g and progress to the 1000 grit.
Sometimes finding 800 and 1000 grit is difficult. Try local Auto Parts stores.....Also. Get yourself a nice big 16 or 18 in sq tile to work on. That's what I use, and it doubles as a cutting board on the counter...I got me a nice piece of marble at a local florring place....I love having something that's a multi tasker. My girl love's the marble on the counter...It's a win win.
Rich