Advice on repairing new knife with broken tip

Japanese Knives - by Tokushu Knife
Kitchen Knife Forums

Help Support Kitchen Knife Forums:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
D

DpC

Member
Joined
Feb 13, 2023
Messages
14
Reaction score
60
Location
UK
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 :mad: :facepalm:
IMG_9592.jpeg
IMG_9593.jpeg

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?
 
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:

1678830730327.png
 
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.
 
Last edited:
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 😅
 
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.
 
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?
 

Attachments

  • IMG_20240111_181238.jpg
    IMG_20240111_181238.jpg
    2.6 MB · Views: 0
  • IMG_20240111_181736.jpg
    IMG_20240111_181736.jpg
    2.7 MB · Views: 0
  • IMG_20240111_181906.jpg
    IMG_20240111_181906.jpg
    2.5 MB · Views: 0
  • IMG_20240111_181916.jpg
    IMG_20240111_181916.jpg
    2.4 MB · Views: 0
valdim said:
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...
Click to expand...
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?
 
Mr.Wizard said:
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?
Click to expand...
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.
 
valdim said:
Note: The tip has been accidentally bended and the vertical black line is where the bend goes. I hope this clarification is useful.
Click to expand...
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.
 
Mr.Wizard said:
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.
Click to expand...
Bending back has already been done. Unsuccessfully. Now I should concentrate on reparing the tip.
 
Heckel7302 said:
....you will be thicker behind the edge than the rest of the blade road.
Click to expand...
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?
 
Last edited:
valdim said:
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.
Click to expand...
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.
 
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.
 
I guess if I follow your advice, the repaired tip should have this shape...
Not bad, in my opinion (if I do it properly).
 

Attachments

  • 17051655138016036669572521028931.jpg
    17051655138016036669572521028931.jpg
    2.2 MB · Views: 0
  • 17051660247456239529800093530443.jpg
    17051660247456239529800093530443.jpg
    2.2 MB · Views: 0
  • 17051660724181668072472383669872.jpg
    17051660724181668072472383669872.jpg
    2.1 MB · Views: 0
You must log in or register to reply here.

Latest posts

Back
Top