Polishing question

[austexchef]

Hey yall,

Newer to sharpening but even more so newer to polishing. This nakamura kaishin got thinned a bit and all I'm trying to do is make an even migaki polish. I have several stones and several set of sandpaper. Stones ranging from S220 to S5000 with various brand and grits in between. Sandpaper grit goes up to max 3000. Do I have to go back to 240grit sandpaper and start over again?

 

[azn_knives_4l]

Hey yall,

Newer to sharpening but even more so newer to polishing. This nakamura kaishin got thinned a bit and all I'm trying to do is make an even migaki polish. I have several stones and several set of sandpaper. Stones ranging from S220 to S5000 with various brand and grits in between. Sandpaper grit goes up to max 3000. Do I have to go back to 240grit sandpaper and start over again?View attachment 328084

Probably not the 240 since those are 220/240 scratches? Depends on what you're going for but the lowest paper greater than 240 seems reasonable to me if you want to remove those vertical scratches.

 

[austexchef]

Probably not the 240 since those are 220/240 scratches? Depends on what you're going for but the lowest paper greater than 240 seems reasonable to me if you want to remove

Probably not the 240 since those are 220/240 scratches? Depends on what you're going for but the lowest paper greater than 240 seems reasonable to me if you want to remove those vertical scratches.

The lowest sandpaper grit I have is 80, it's super rough to the touch. Do I start there and just get an even super scratched surface and then just work my way up?

 

[azn_knives_4l]

The lowest sandpaper grit I have is 80, it's super rough to the touch. Do I start there and just get an even super scratched surface and then just work my way up?

Nope! Idea is to figure out what caused those deep vertical scratches and go *higher* than that to remove them without the risk of creating more.

 

[austexchef]

Nope! Idea is to figure out what caused those deep vertical scratches and go *higher* than that to remove them without the risk of creating more.

Ah I see, I'm not super concerned about the vertical scratches at the moment, more the hazy patchwork from thinning on my king 1000 and Shapton 5000

 

[azn_knives_4l]

Ah I see, I'm not super concerned about the vertical scratches at the moment, more the hazy patchwork from thinning on my king 1000 and Shapton 5000

Ahhhhhh. That just takes practice, unfortunately. Pretty tough to polish a convex surface with a synthetic rock and *not* leave streaks.

 

[bsfsu]

Polish the hagane up to your 5000 stone then go back to the jigane on a lower grit stone, then even out the finish with sandpaper. I prefer to use uchigumori powder instead of sandpaper, it evens out the finish from stones a bit better.

The finish depends on how good your low grit work was, work on consistent scratch patterns, lighten up on the pressure that you use to limit the deeper scratches. Practice.

 

[M1k3]

Easy mode:

1. Not care about the vertical scratches.
2. 400 grit sandpaper, going from spine to heel, heel to spine.
3. Cut stuff

Not so easy mode:

1. 240 grit going edge to spine, spine to edge.
2. 400 grit going from spine to heel, heel to spine.
3. 800 grit going edge to spine, spine to edge.
4. 400 grit sandpaper, going from spine to heel, heel to spine.
5. Cut stuff.

 

[Benuser]

As a general rule, scratches only can be removed by the same grit as what caused them. That said, it's far from easy to establish what the grit was. A trick I got here was to start with evidently too fine a grit, gowing lower until you've found the right grit for those scratches, and from there going up again.

 

[austexchef]

I guess what I'm asking is, can I remove the cloudy dull inconsistent spots with sandpaper starting at an 80grit to even it out and then move up from there?

 

[Benuser]

With coarse sandpaper you're likely to deepen the low spot. See it as a valley: the only way to even it out is by removing the surrounding hills.
You may try with a coarse stone. Sandpaper, and much finer, only to get an even appearance if the low spot is too deep.

 

[Martyfish]

I guess what I'm asking is, can I remove the cloudy dull inconsistent spots with sandpaper starting at an 80grit to even it out and then move up from there?

It sounds like you just want it look decent again, which is very doable in 30 minutes or so with sandpaper. I'd start around P240-320 grit, because sandpaper in this grit range can still remove scratches, but it is also pretty quick to progress up to a nice working satin finish once you have an even base finish. I'd stop around P600-800 grit, because it looks good and isn't fine enough to start causing food to be suctioned to the blade.

I documented the refinishing process after thinning in the link below, which is applicable to your situation. Start from step 10 and after 30 minutes or so you should be at step 15 and have a decent finish.

 

[ile74]

Ah I see, I'm not super concerned about the vertical scratches at the moment, more the hazy patchwork from thinning on my king 1000 and Shapton 5000

If the scratches are coarsest #1000 grit, I would even out with #400 sandpaper or sanding felt. #400 grit gives quickly low maintenance and carefree hazy finish so you don't have to worry little scratces by wiping, washing and abusing the knife in use.

I wouldn't say #1000 grit is thinning. I have tried to learn sharpening with waterstones for 3 years. I started with #1000, #3000 and 6000#. Those are mostly for stropping and first sharpenings for really thin knife, but too slow even maintenance thinning. I messed up many knives geometry when tried to thin #1000. It's so slow that I wanted to speed up by lifting spine and then I got convex, thick behind edge geometry.

I recently purchased real thinning stones #80, #120, #180 and #320 grits. Shapton #320 was very enjoyable at repairing minor convexity and thick geometry in my previously messed yanagi and usuba. #120 and #180 are good if you need serious thinning and I have used them at double bevel knives. I try to do slowly and focused when using coarse stones. 2-5 strokes, stop, check if you have correct angle and pressure, rinse and repeat.

My typical mistake in sharpening the tip was not lifting the heel and I got low spot near the tip (red lines). Keep an eye to lift up heel to keep correct angle. Your knife is not messed yet, but I fear it's going to be if you continue that way. Just repaired one funayaki, what I messed really bad at first sharpening two years ago with SG #1000. There was serious low spot near the tip and edge was recurved as a bird's beak. That repairing and shaping was done quickly with #80 stone.

 

[cotedupy]

Hey yall,

Newer to sharpening but even more so newer to polishing. This nakamura kaishin got thinned a bit and all I'm trying to do is make an even migaki polish. I have several stones and several set of sandpaper. Stones ranging from S220 to S5000 with various brand and grits in between. Sandpaper grit goes up to max 3000. Do I have to go back to 240grit sandpaper and start over again?View attachment 328084

So… do you want a polish that is aesthetically even across the ‘shinogi’? The same on the kireha and the hira?

Cos that knife hasn’t been forged or ground to make that possible on stones, you’d have to completely re-work the geometry of the whole blade face on both sides. You can do that with very coarse sandpaper or stones, but it’ll completely change the knife. Otherwise if you do want an even polish across the whole face, then you’ll need to use just sandpaper (and/or; compound, powder, fingerstones &c.), not benchstones.

The vertical ‘scratches’ on the hira, as you probably know, are grind marks from when it was made. And they’re fairly deep and fairly coarse. They’re not going anywhere soon unless you’ve got a belt grinder.



p.s. If I’m completely misunderstanding your q. then do please ignore me!

 

[The Forest Ninja]

When they polish Japanese Katanas they use a different angle to polish with
early on with each new stone and that helps them to see if they eliminated
scratches from previous stones. Using the same tactic with Sandpaper could
help in figuring out where to go back if the polish isn't perfect.