Does my gyuto need thinning?

[Carl Kotte]

Very wise!

And good luck! Come back with a report on the result!

 

[Jville]

I suspect it will be back to blazing through onions.

 

[M1k3]

I just remembered another tip! Use a sharpie on the blade face. It'll show where the high and low spots are as you're thinning. Be warned, you may get sad at how uneven it is.

 

[oval99]

OK, so things are heading in the wrong direction I spent about an hour on my coarse 220 Shapton stone thinning the bottom 1/3 of the blade. I marked with a sharpie the bottom third and checked to see if I was removing it. I was. But instead of things getting better, they got progressively worse. Now the knife REALLY wedges in onions, way worse than before. Two choil shots below: one on the top is new, bottom one is the previous shot before thinning.

I have three theories about why this is happening:

1) I've applied unequal pressure when thinning, and some parts of the knife are thinner than others
2) I've concentrated too much near the edge of the knife and not further up towards the "shoulders" -- judging by my new pic, I think this is the culprit. The old pic (one on the bottom) has a profile that is more "straight" (like a razor blade) whereas my new pic seems to bulge out (get "shoulders") much earlier from the edge. Perhaps I need to work exclusively on the area further away from the edge (about 1/2" or so).
3) The blade is becoming dull from all the thinning (unlikely)

Anyone know what's going on?

 

[M1k3]

You need to get roughly 2/3rds of the way up.

 

[oval99]

Wow, that will take a long long time! Thanks for the tip though

 

[refcast]

Try polishing the surface a bit with sandpaper, metal polish, or bar keeper's friend. Often after going really coarse, I find the surface left over is really grippy to food and causes wedging not due to geometry, but due to surface finish. Like splitting a log with an thin axe covered in sandpaper vs a thick axe that has a smooth finish.

Your point (2) does have some merit. I do get better food release and splitting of food with shoulders. So it sticks less that way. Both ways are valid and up to preference or situation (thinning close to the edge vs higher up the blade).

 

[Nemo]

Also remember when I got it back from Dave — same Ferrari performance.

Are we talking Dave Martell? If so, that's certainly a good benchmark.

 

[lemeneid]

This is why I never recommend novices do any thinning. Why on earth would you need to thin a laser anyway? Takamura, Shibata, Ginga, etc are all thin enough they don’t wedge and naturally thin if you sharpen correctly with good technique and angles.

To OP, you can’t judge the knife’s geometry from a choil shot. All it does is show how the knife looks at the heel.

Unless you’re ok with making this a project knife with the possibility of making things worse, I suggest taking it back to Dave Martell and getting him to fix up the knife for you. It will cost you but at least you don’t do anything irreversible. He can at least look at it and tell you professionally what happened because there is only so much pictures can tell how the grind has changed.

Otherwise if you’re making this your project knife, thin away!

 

[Jville]

After you thinned on a 220 did you sharpen it?

 

[lemeneid]

IMO you’ve probably created a thick secondary bevel on the edge which is why the knife isn’t cutting well and that needs to be fixed with very aggressive angles or even laying the blade flat on an equally flat stone. You will probably screw up the finish on the knife doing this but that would be my way forward with the little information I have. Which is why I recommend getting a professional fix this for you because there is no way of knowing what’s wrong without working the knife personally.

 

[labor of love]

gingas, tads, takamuras indeed start to suck if they’re sharpened over and over again and never thinned. But these are some of the easiest knives to thin IMO. A little can go a long way. It is suspect that this knife is performing poorly after only six sharpenings but the choil shot for an ootb takamura should be a lot thinner than what you demonstrated in the photo.
I’m not sure anyone had ever thinned a knife really well the first time. Keep studying, watch thinning videos and practicing. Can you take photos of your thinning scratches?

 

[lemeneid]

gingas, tads, takamuras indeed start to suck if they’re sharpened over and over again and never thinned. But these are some of the easiest knives to thin IMO. A little can go a long way. It is suspect that this knife is performing poorly after only six sharpenings but the choil shot for an ootb takamura should be a lot thinner than what you demonstrated in the photo.
I’m not sure anyone had ever thinned a knife really well the first time. Keep studying, watch thinning videos and practicing. Can you take photos of your thinning scratches?

You’re definitely right with that, that’s why I found it baffling thinning was started on a really aggressive 220 stone. If anything, and the wrong angles, you probably ended up with too thick an edge too quickly. Should have started on the 1500 like some others recommended.

 

[Knife2meatu]

OK, so things are heading in the wrong direction I spent about an hour on my coarse 220 [...] But instead of things getting better, they got progressively worse. Now the knife REALLY wedges in onions, way worse than before.[...]

I have three theories about why this is happening
[...]
3) The blade is becoming dull from all the thinning (unlikely)
[...]

I'm nowhere near knowledgeable on any of this -- but perhaps this advice is best given by an admittedly rank amateur: If I'm correct in the assumption that you're doing all this thinning with the edge still sharp and intact, I would suggest you consider perhaps instead dulling it beforehand next time.

I've found that the force involved in thinning, a moment of unforeseen stiction, fingertips, and a really sharp edge, can make for a painfully memorable mix.

 

[oval99]

All,

I have some results to report. They're pretty anticlimactic, really. After a long session on an Atoma 120 diamond plate, nothing really seemed to happen (other than taking off a metric ton of steel, of course). Profile didn't change much, and performance perhaps improved a tad, but it still wedges badly on onions. And yet it still cuts incredibly well for just about everything else I prep (tomatoes, scallions, bell peppers). Also didn't wedge TOO badly in carrots.

And yes, I've dubbed this my test/project knife. The scratch patterns don't bother me -- it doesn't need to hang in the Louvre. If all else fails, I'll send it to Dave and see if he can fix it when funds allow.

Below are some pics of the scratch patterns:

 

[labor of love]

Well I’m glad to know you have a contingency plan.
With your diamond plate you thinned quite a bit up the blade. What happens here is that your focusing your pressure on a broader area instead of a small area, the impact felt from thinning won’t be as effective. If you just put pressure on a smaller area you should feel the results sooner. Your finger tip placement decides the pressure as long as you’re laying the blade flat on the stone. Shorter thinning strokes (like 3 inches forward and back) guarantees better repeat/hitting the same spot over and over again and removing metal from the area as opposed to going all the way from the bottom of the stone face to the top(really long 8 inch strokes).
If you want to feel progress sooner and I’d focus my pressure closer to the edge, use shorter strokes, focus on repeating the same spot over and over again as I work my hands down the blade.
Nothing I’m saying here is written in stone as law. But it does work well for me.

 

[labor of love]

Did everything I say make sense? Let’s have so more discourse before your next thinning session.

 

[TurboScooter]

Try polishing the surface a bit with sandpaper, metal polish, or bar keeper's friend. Often after going really coarse, I find the surface left over is really grippy to food and causes wedging not due to geometry, but due to surface finish. Like splitting a log with an thin axe covered in sandpaper vs a thick axe that has a smooth finish.

Your point (2) does have some merit. I do get better food release and splitting of food with shoulders. So it sticks less that way. Both ways are valid and up to preference or situation (thinning close to the edge vs higher up the blade).

IME this is absolutely a valid consideration.

It's tedious as fvck if you end up wanting to go further in your thinning job, but I basically refinished my blade to test if I was happy with my thinning job. With the finish left by a coarse stone it drags badly and you can't really tell what the performance will be like once you refinish the blade.

 

[labor of love]

Yeah, this is true. I Atleast finish my thinning with a chosera 400 or a 1k or micro mesh pad polish before I test how it cuts.

 

[labor of love]

Also, there’s nothing really wrong with thinning that high up the blade if you want to(with the atoma) but results will take longer.

 

[McMan]

Well I’m glad to know you have a contingency plan.
With your diamond plate you thinned quite a bit up the blade. What happens here is that your focusing your pressure on a broader area instead of a small area, the impact felt from thinning won’t be as effective. If you just put pressure on a smaller area you should feel the results sooner. Your finger tip placement decides the pressure as long as you’re laying the blade flat on the stone. Shorter thinning strokes (like 3 inches forward and back) guarantees better repeat/hitting the same spot over and over again and removing metal from the area as opposed to going all the way from the bottom of the stone face to the top(really long 8 inch strokes).
If you want to feel progress sooner and I’d focus my pressure closer to the edge, use shorter strokes, focus on repeating the same spot over and over again as I work my hands down the blade.
Nothing I’m saying here is written in stone as law. But it does work well for me.

I agree with Labor.
You can the importance of finger pressure/location at 2:20.
I should've posted this earlier... better late than never.

 

[labor of love]

I’ve always loved that handle on Jon’s Zakuri!

 

[krx927]

In my opinion you now need to do 2 things to really evaluate your thinning result:

1. you need to refinish the knife a little bit (or fully) and get rid of the thinning scratches. There are many threads on KKF about this. If you need some help we can give you further pointers.
2. You will need to resharpen your knife. In my experience you always loose the sharpness when thinning even if you think you are not touching the cutting edge.

 

[M1k3]

Hopefully the photo shows how high I go. It's nearly flat where it doesn't look pretty and convexes (hamaguri) at/near the edge.

 

[Jville]

Could you also show another choil shot, because youve thinned more since your last pic?

 

[M1k3]

Could you also show another choil shot, because youve thinned more since your last pic?

Me? I'm not OP but I'll attach pictures of it

 

[Jville]

Me? I'm not OP but I'll attach pictures of it

I thought these were before he finished thinning, tweener pics.

 

[oval99]

The avalanche of advice is frankly amazing! I’m blushing, truly. I particularly appreciated labor of love's, well, labor of love in his in-depth responses.

But I also know when I’m in over my head; I feel like I have bees buzzing in my head from all the info. I think lemeneid has the right idea: when my funds allow, I’ll send it to Dave Martell and see what he can do to repair it. More importantly, I’d love to know WHAT he did to it and where I went wrong. Otherwise I know I’ll find myself in a quicksand.

This is what is so insidious about learning this stuff over the net: it only takes me so far. I tend to learn by having a decent framework of the concept (YouTube vids and this forum help here), then doing the task, making mistakes, and then having an expert in person show me where I went wrong. THEN the concept really sinks in; then I am truly learning from my mistakes —from my experience.

You ever had to read/watch training material for a new skill, take and pass the test but the concept is still foggy, then struggle on your own and make mistakes by directly using the skill/product, and THEN go back to the training materials? For me, that’s when I truly read/understand the training materials — once I have the fumbling/infuriating/exhilarating first-hand experience of wrestling with the damn thing, then I truly understand the concepts. Perhaps I could talk with Dave after he’s sharpened/repaired my knife about what he did (and what I DID) so it can really sink in first-hand.