Need help with tip repair

[jnbrown]

Hi,

I have a Shun 3.5" paring with a broken tip (see picture).
I am wondering if I should grind from the blade side, the spine, or some of both to restore the tip.
The coarsest stone I have is 600 grit which I don't think will work, so I am wondering if a can use sandpaper on a granite slab to start.
I also have CKTG 140 diamond plate but would like to use it for flattening only,
I am afraid I could damage by using it on a knife.
I also have a Rigid spindle sander that has a belt attachment.
Right now it has an 80 grit belt but I could order something with finer grit.
Thanks for any advise.

[d_rap]

Of course I see in your post that you want to avoid what I'm going to suggest but I still think it's the right course. Your cktg 140 plate is a very good tool for that job. It's affordable, and in any event if you stroke gently, using different parts of the stone, you won't damage it. Yes tip repair represents a kind of wear to a diamond plate but you can do many such repairs and still use that plate for flattening without any problem.

I would go some from the spine and edge (most even results) drawing the knife toward you, checking the results after every stroke or two to make sure you feather the edge nicely.

It's a small knife, forgiving steel and an aggressive plate. Try even a couple of easy strokes and you'll see why I'm making the suggestion.

I have used that plate on a number of tip repairs with good success and no gouging.

[Chappychap]

Just to add to David's reply, I had a similar tip situation and followed the above approach pretty much. Happy with the result in terms of losing as little as the tip as possible, minimal work, and minimal wear to my CKTG plate. In general you want to repair from the spine side first if you can, as this will affect blade geometry the least. If you go from edge side upward you can end up with a 'fatter' tip than the rest of the knife has , as you'll be eating into the grind. This can result in needing to then thin at that part as well, which is obviously best avoided if you can.

One thing to consider is some fine grit sandpaper to polish off the part that you grind down, if aesthetics matter to you.

[Jeff B]

Start off with a low grit sandpaper on a flat surface to do the heavy lifting and work from the spine down. Use the plate for the final shaping or stick with sandpaper for all of it. Sandpaper is cheap and will save some wear on your diamond plate. Use a higher grit sandpaper to polish the spine after you get the tip the way you want it.

[jnbrown]

When I am grinding the spine I assume the knife should be perpendicular to the diamond plate.
How about from the blade side? The same angle as normal sharpening?

Thanks

[Jeff B]

I would do the entire repair from the spine side. No need to grind on the edge side for that repair. Take the top point of the break down to the bottom point of the break.

[d_rap]

And either way, edge or spine, you're going to want to work perpendicular to the plate because you're trying to cut steel away to create a new tip before you re-sharpen. Gently dragging the edge side along the 140 perpendicular to it works fine.

That said makes sense Jeff. Certainly the path of least resistance.

[Jeff B]

001.jpg (19.49 KiB) Viewed 1757 times

[d_rap]

Sold!

Nice. Thanks for that Jeff.

[jnbrown]

Thanks Jeff.

[ken123]

You want to smooth the spine out with a finer grit rounding the edge. You can develop a burr on both sides of the blade FWIW
Ken.

[jnbrown]

Here is the restored tip.
I am pretty happy with how it turned out.
I mostly used sandpaper, but I did try using the CKTG diamond plate.
It was pretty obvious that the plate was much faster and better and I used very light pressure.
But still I was afraid of ruining the plate.
I do have some scratches on the sides of the blade.
Not sure if I should try to polish those out or just not worry about them.

[d_rap]

Looks like you got some good results there. Glad it worked out.

There's some good discussion here on the forum about scratches but that would be a whole 'nother project, so if you're okay with them leave them. Repairing scratches thoroughly really means refinishing the whole blade surface, but there is also some touch-up level stuff you can probably do depending on the details.

[Chappychap]

Looks like you did a great job! I hope it was also a confidence-building experience - I know my first tip repair job was a huge one for me.

[PaulME]

Late to the party but you really should not be concerned of the diamond plate. When used on steel the “wear” on the plate is really the risk of the diamonds coming out - any normal pressure is not an issue. Won’t go into the other thing that can happen with diamond an carbon steer - safe to say it will NEVER occur with hand sharpening.
Realize diamond wheels are what is used to cut and shape carbide cutting tools - lots harder than steel.
Paul

[David_R]

Late as well. That looks great. I had a similar knife with a similar tip. I got impatient and ground the spine side on my bench grinder. One second on the grinder, then into water. I also had to chamfer the spine with a stone where I used the grinder. I did spine side only so I didn't change the edge profile.