Saji rainbow 210 gyuto thinning

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cheeken1111

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Long time lurker "first time" poster. Let me know if I messed anything up or any constructive feedback.

Didnt see any colored/rainbow damascus thinning threads.... well anywhere and had a fat Saji 210 gyuto that probably wouldnt see much use as is. I would guess most people who buy these flashy knives want to keep them flashy.

Also an interesting note is that i have two 210 saji rainbow damascus in B1.
20230502_223553.jpg


They are ground quite differently. The wa handle was quite fat behind the edge, while the yo handle is in the middle. The blade height of the yo handle is shorter and has a flatter profile. Both have vertical scratches that have been polished, no distal taper and quite stiff blades.

wa handle
20230502_223617.jpg


yo handle
20230502_223634.jpg


I was also curious on hardness. I have the "cheap" hardness tester files and gave the core on both yo and wa a light scratch. Both skated the hardest "65" hrc file. Pushed about how hard you would a pencil eraser while.... erasing pencil. Didnt go full bore incase i put down a scratch i cant take out..... Also was curious to test the stainless cladding which the 40 hrc file bit into immediately. No point testing the copper or brass......

20230502_223810.jpg


My progression was
- shapton 120 kuromaku ~30 min
- knifewear 220 naniwa ~ 5min
- shapton 1000 kuromaku ~5min
- 2000 green brick of joy ~20 min ( my weak side still showed oem vertical scratches so i dropped back to 220 a couple times)
- shapton 5000 kuromaku ~5 min
- shapton 8000 kuromaku ~5 min
- shapton 12000 kuromaku ~5 min

My main stratagy was to raise the primary bevel/shinogi line and not apex or touch the micro bevel. This was done by the left hand pressing on the opposite side shinogi line instead of center of the bevel and edge.

Had some learnings and it didnt turn out perfect but ill get it on the next sharpening/thinning. listed below

- Although there is a crappy scratched polished finish the bevels were suprisingly flat. No low spots in the bevels anywhere
- On the right side of the blade there is a low spot on the head and heel of the knife. I think its from the hot cut process after forging over size then taking a shear to cut the profile.
- It was pretty easy not to apex the micro bevel based on how fat the grind was.
- Clear low grit slurry often. Got a few scratches on the top flats.
-Probably dont try to finish in one night...... had a few slips and the finish/smoothness is not so great at the top of the primary bevel.
- Indoor lighting sucks for photos


Okay enough fore play here are the grinding photos

shapton 120
20230502_233815.jpg



naniwa 220
20230502_234936.jpg


shapton 1k, you can see the vertical scratches on the belly of the core steel i had to go back to 220 for.
20230503_000140.jpg



2k brick, ignore the dishes I am putting off doing
20230503_003303.jpg


Shapton 5k, you can see on the flats the verical grind lines from factory. If you see horizontal or diagonal grind lines.... that was me mesaing up.... least i can buff them and pass them off as factory.
20230503_004058.jpg


Shapton 8k can now see the clad line between core and stainless.

20230503_004603.jpg



Continued in next post due to pic limit
 
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shapton 12k
20230503_005137.jpg


finished profile was more or less set after 120 grit.
20230503_005408.jpg

another....
20230503_005257.jpg


Probably can use another thinning but a bit better than before.


Some areas of interest.

left side, edge of the heel and the edge of tye shinogi line are "bent".
20230503_005421.jpg

left side, tip was proabably me not lifting enough to polish
20230503_005428.jpg


Right side, tip i could not get the bevel to go all the way to the "head". in the previous photo there was no such issue. Also I am right handed so this is my "strong side" bevel sharpening.
20230503_005437.jpg


Right side, heel with not much issue.
20230503_005441.jpg


Let me know at what grit i should have stopped at. im partial to the 5 or 8k where there is some kasumi on the stainless cladding..... maybe i should take it to my natural stone..... yes singular.... i only have one.

Probably will round the choil and spine next and try to blue the core steel.... i am a turd polisher at heart.

Never formed a burr so probably still factory edge =) just not factory bevels. Thanks for reading and bearing with my crappy grammer and formatting.

Cheers.
 
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I actually did this with my santoku of the same make (saji rainbow b1). Similar progression starting with nanohone 70um (200grit), Jki 1k diamond, 3k naniwa pro, 9k morihei. Then I did wet/dry sandpaper with wd40 up to 1500 (400, 800,1500 progression) on the whole thing. I’m really pleased with the overall performance and aesthetic now that it’s thinner and less…shiny (I wasn’t a big fan of how blinding shiny they are with the default finish). I’ll have to take some pics and post them later.

Some notes on my experience: I had to deal with some low spots and uneven cladding, but the thinning resolved that (with some work!). The sanding removed the kanji, which is unfortunate, but the style is so unique, I don’t think it can be mistaken for another knife.
 
Are you sure that heel is not just thicker instead of bent? Quite common seeing an abrupt thickening at the heel. By the way: never performed a thinning that hadn't to be followed by at least a touching-up of the edge. Although the edge hadn't been touched.
 
I actually did this with my santoku of the same make (saji rainbow b1). Similar progression starting with nanohone 70um (200grit), Jki 1k diamond, 3k naniwa pro, 9k morihei. Then I did wet/dry sandpaper with wd40 up to 1500 (400, 800,1500 progression) on the whole thing. I’m really pleased with the overall performance and aesthetic now that it’s thinner and less…shiny (I wasn’t a big fan of how blinding shiny they are with the default finish). I’ll have to take some pics and post them later.

Some notes on my experience: I had to deal with some low spots and uneven cladding, but the thinning resolved that (with some work!). The sanding removed the kanji, which is unfortunate, but the style is so unique, I don’t think it can be mistaken for another knife.
Would definately be interested in seeing another example. Also definately agree, there arent many rainbow/colored damascus out there. The kanji really is barely on there.

Do you have the vg-10/b2 and yo/wa version? I was suprised how differently they are ground on my example. Guessing different person grinding each type. But only have a sample of 2. =/

How did you use the sand with the sand paper? Im guessing not with fingers. seems like a good way to get sliced.
 
Are you sure that heel is not just thicker instead of bent? Quite common seeing an abrupt thickening at the heel. By the way: never performed a thinning that hadn't to be followed by at least a touching-up of the edge. Although the edge hadn't been touched.
Feeling up and down the heel doesnt seem to get thicker but would need to put some calipers on it to be sure. By bent I meant the line didnt grind straight even tho I was grinding flat on the bevel. Perhaps clarifying there is a radius on the heel possibly from pinching during the profile shearing process.

I too was suprised too that I didnt form a burr or have any roughness on the edge after the 120 grit step. I would have assumed the slurry atleast would build up and touch the edge. I guess thats how wide the micobevel was due to thick it was behind the edge. When thinning I was pressing higher up on the bevel basically applying pressure on the shinogi line so maybe kept the removal away from the edge.
 
The changes in the very edge weren't due to slurry, as I could verify. My guess is it had to do with the used pressure.
 
Here are the original shots:
Original.jpg

original 2.jpg

And here are the shots after thinning a little and sanding:

IMG_5518.jpg

IMG_5519.jpg


As for the sanding, I just braced the wood against a block of wood, with the flat of the edge almost flush to the wood (handle was not on the wood / was used as a bit of a brace to keep it steady while sanding). Ideal would have been to have a vice or clamp, but you work with what you have.
 
Here are the original shots:
View attachment 241281
View attachment 241282
And here are the shots after thinning a little and sanding:

View attachment 241283
View attachment 241284

As for the sanding, I just braced the wood against a block of wood, with the flat of the edge almost flush to the wood (handle was not on the wood / was used as a bit of a brace to keep it steady while sanding). Ideal would have been to have a vice or clamp, but you work with what you have.
Funny that the vertical grind lines are deeper than the kanji. Also am suprised how well these come out.
 
Yeah seriously. I could probably go at it harder with sandpaper, but I'm satisfied with how it came out. I think sanding off the polished finish brings out the colors of the copper and bronze even better.
 
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