Advice on repairing new knife with broken tip

[DpC]

I came home today to find my cleaner had decided my new (literally used once) Yoshikane KU Tsuchime Petty 150 was - despite having been warned never to touch my j-knives - an appropriate cleaning tool: broke and rounded the tip, dulled the edge, scuffed up the cladding, and apparently cut her hand in the process

Cleaner fired, but how do I salvage my new knife? I'm a novice sharpener and have never done a serious repair job. I figure I need to work on getting the tip back first and then try to maintain the edge geometry? Do I need to thin afterwards (I guess that will remove the nice KU )?

Currently my stones are Naniwa Pro 1000, 3000, BBW, SG 6000...guessing I'll need a lower grit stone? Would SG 220 or Naniwa Pro 400 work?

 

[deltaplex]

Any of those stones will work, either the SG220 or the NP400 would be a bit faster at removing the metal. I usually end up using the side of the stone for this since it takes a little care to not end up with a line ground into the surface of the stone, and it matters relatively little to me if the side of the stone has a gouge in it for re-profiling tips. I'd personally do most of the material removal from the spine side (red lines), but you could choose to bring the edge up to meet the spine if you didn't mind the tip further drifting up from the edge profile (blue line). Either way you'll need a little bit of blending to make the repair look relatively seamless; excuse my rough markup, it's just to give a general idea:

 

[Nemo]

Ahhh... Your first tip repair. Very likely it won't be your last. Don't ask how I know.

I hope that your cleaner didn't injure themself badly.

This is a small tip injury and should be a quick and easy fix. Like 5 or 10 minutes. Plus resharpening.

Most of the work can be done with any coarse stone. I have used chosera 400 or sandpaper on a Kasfly sandpaper holder for this in the past.

Obviously be careful not to cut yourself. I tend to dull the edge by breadknifing very gently on a fine stone before doing any serious grinding or refinishing work. This technique makes it much easier to restore the edge later on.

Grind from the spine side (the spine is pressed against the stone, with the edge pointing directly up) until you have generated a curve that suits the blade and meets the intact edge. The red line in the picture above is in the ballpark. Keep in mind that the edge will rise slightly with suhsequent resharpening, so you may not need to get 100% to the intact edge. Consider using a sharpie to draw the approximate curve that you want to achieve. Grind little bits at a time and check where you need to focus on the next dozen or so strokes. Changing the angle that you hold the knife to the stone throughout the stroke will help smooth out your curve. For reference, the steepest angle that you hold the knife at (the angle between the handle and the stone) should be in the ballpark of 45 or 50 degrees.

Don't grind the edge side unless you want to do the thinning and geometry correction that will result. Much more work and much more room for error.

If you wish, you can chamfer or round the edges of your newly ground spine and/or refine the finish with a finer stone (or sandpaper).

Then resharpen the knife.

 

[DpC]

Thanks for the advice! Have ordered a NP400.. will try the spine removal approach when it arrives. Also consoled myself by impulse buying a Toyama dama 150 petty

 

[Benuser]

For the steel removal at the spine alone, I like to use a nail file. The NP 400 will serve you very well for the light thinning behind the edge and sharpening of the new tip once spine and edge meet again.

 

[DpC]

Finally got around to doing this today - pretty happy with the results:

 

[ian]

Did you end up grinding from the edge rather than the spine?

 

[deltaplex]

That's how it appears to me.

 

[DpC]

Did you end up grinding from the edge rather than the spine?

No - I did it from the spine. Though starting a little further back (i.e towards the heel) than shown in @deltaplex’s diagram. Then I put a new edge on it starting from the NP400.

 

[stringer]

No - I did it from the spine. Though starting a little further back (i.e towards the heel) than shown in @deltaplex’s diagram. Then I put a new edge on it starting from the NP400.

It looks great. Nice repair

 

[HumbleHomeCook]

Nice job!

 

[gaijin]

Well done!

 

[ian]

No - I did it from the spine. Though starting a little further back (i.e towards the heel) than shown in @deltaplex’s diagram. Then I put a new edge on it starting from the NP400.

Looks great.

 

[The_Real_Self]

Ah.... yes.... but the real question is did you TIP her for her services after she cleaned your house? You have to appreciate those who go above and beyond their duties...

 

[valdim]

A useful thread and further advices...I will face same issue soon. Thank you, all invoolved.

 

[valdim]

This is my first tip repair and I am indulging it.
I want to keep the profile of the knife and in My opinion that means to keep the "slopes" both from the edge side and the spine. The latter is more steep. That means (as per my humble aesthetic understanding), that I will have to grind as per the marked black lines.
I I have some concern from the fact that I would be taking more material from the edge, than from the spine...But may be it is not such a big deal... Huh?

I will work with whetstone SG 320 and may try nail file on the spine line.
The vertical line (7 mm) is where the tip bending ends.

Any concerns? Opinions on my working plan?

 

[Mr.Wizard]

I have some concern from the fact that I would be taking more material from the edge, than from the spine...But may be it is not such a big deal...

I always prefer to remove from the spine side only for preservation of the original grind, but I have only done this on western and western-pattern knives. It seems to me that if you are comfortable working the full height to the shinogi line and you don't mind significant work thinning you can effectively do a regrind to restore the geometry.

Taking a close look at your drawing I don't see why you want to remove so much metal however. Why are you planning to move the tip well back from the existing break?

 

[valdim]

Taking a close look at your drawing I don't see why you want to remove so much metal however. Why are you planning to move the tip well back from the existing break?

Which metal you mean, the section from the spine side or the opposite section?
I didn't understand the above quoted question, too...
Note: The tip has been accidentally bended and the vertical black line is where the bend goes. I hope this clarification is useful.

 

[Mr.Wizard]

Note: The tip has been accidentally bended and the vertical black line is where the bend goes. I hope this clarification is useful.

Okay, I misread what you meant by "tip bending" but now I see. If it was malleable enough to bend perhaps you can bend it back? I realize it may work harden and snap, so care would be needed not to make the problem worse, but if it were my knife I would try.

 

[valdim]

Okay, I misread what you meant by "tip bending" but now I see. If it was malleable enough to bend perhaps you can bend it back? I realize it may work harden and snap, so care would be needed not to make the problem worse, but if it were my knife I would try.

Bending back has already been done. Unsuccessfully. Now I should concentrate on reparing the tip.

 

[Heckel7302]

I would still only grind down the spine side. If you grind up the edge side you will be thicker behind the edge than the rest of the blade road.

 

[valdim]

....you will be thicker behind the edge than the rest of the blade road.

Unless I thin it. Although, I am not sure I can do the thinning properly, though I have the stones (1000, 2000, 4000, 5000)... Never done thinning in such case.

If I thin from the spine only, I am afraid I would change the aestethics and the initial idea of the bladesmith. And I would like to preserve them.
I was thinking about making K-tip, too, but ...that means to change the knife tip and shape even more...
The length of the edge area that i have to remove is like 30 mm... @Heckel7302, are you sure removing that lenth would have the above effect?

 

[Heckel7302]

In my opinion maintaining the blade road is much more important than maintaining the spine shape. The latter has very little affect on how the knife is used. It’s just aesthetic

 

[Mr.Wizard]

Unless I thin it. Although, I am not sure I can do the thinning properly, though I have the stones (1000, 2000, 4000, 5000)... Never done thinning in such case.

Unless that 1000 stone is something special you will struggle to do that much thinning with it. If you want this as a learning project so be it, but know what you're getting into with open eyes. It's a lot of work and far from trivial skill if aesthetics are important.

I forgot you said you will use SG 320. I haven't used that particular stone but I hope it is much much faster than a Cerax #320.

 

[myguidingmoonlight]

With knife tipping I always grind spine direction down to meet the edge.

In my experience, this is much easier than thinning the entire tip bevel. Even if I have to turn it into a santoku.

 

[valdim]

I guess if I follow your advice, the repaired tip should have this shape...
Not bad, in my opinion (if I do it properly).

 

[Pie]

Finally got around to doing this today - pretty happy with the results:View attachment 235035View attachment 235036

Now this is one hell of a first try. Well done.