Knife repair

S Clark · « **on:** 19 Jul 2020, 09:19 pm »

I keep falling further and further down the Japanese knife rabbit hole... Rob B. warned me years ago about this danger.
I've found another damaged knife to try to bring back. This one is a deeply chipped SG-2 powdered metal knife by the giant megacorporation Kai/Shun.... the very knives they are being sued about for blades that are too chippy (hard and thin). When it arrives, it's going to take some major reshaping to save it.
I might VERY judiciously take some off with a belt sander, as this steel is not supposed to surrender easily. Or, I might do it with diamond stones by hand... just have to see how difficult it is to work with.
Mr. Babcock, any suggestions? The SG2 is supposed to be nearly identical to R2 steel.

WGH · « **Reply #1 on:** 19 Jul 2020, 10:14 pm »

You will need sanding belts designed for stainless steel like the Klingspor Aluminum Zirconia 411, "Suitable for most metals, alloys, hardwoods, aluminum, brass, bronze and stainless steel".
It never gets dull but because it is coarse there will be a lot of scratches to slowly work out. This is the only sandpaper that holds up to mesquite.

Matching the same blade curvature by rotating the point up and keeping the heel the same it looks like you loose 1" off the tip, that's a lot of honing.

S Clark · « **Reply #2 on:** 19 Jul 2020, 10:56 pm »

Wayne, thank for the tip on the belt. This is a 3 1/2" paring knife, and by the photo, I was thinking about taking about 1/8" off the heel and shortening the knife by about 3/8" to 1/2". Of course the damascus cladding will need to be thinned as well. If it turns out to be a real bear to remove the steel, i have a friend that has a Tormek machine... I'd just use the knife as an excuse to visit. But in these times, that may be a while, so I'll look for a source for the Klingspor belt just in case.

sts9fan · « **Reply #3 on:** 19 Jul 2020, 11:50 pm »

I’m a hobbyist knife maker. That’s quite a bit up the bevel. It definitely won’t cut the same but should be fine. The Shun classic are quite brittle. I have a set I used before I got into the “more expensive the audio” custom knife game. A bunch have chips. To re-profile you really should use a 2x72 grinder with ceramic belts.

sts9fan · « **Reply #4 on:** 19 Jul 2020, 11:53 pm »

I want to add, go slow and don’t heat it up too much. You don’t want to screw with the heat treat.

S Clark · « **Reply #5 on:** 20 Jul 2020, 12:24 am »

The Shun Classic is VG10 or VG-Max steel- close to the same. Both are much softer and less wear resistant than the SG-2 powdered steel, and not as brittle (even though they are brittle for that steel). I'm very aware of how amazingly fast a belt can ruin the temper, especially near the tip (ruined a screwdriver or two over the years). I've got some coarse diamond plates to try first. Hopefully I can do it all by hand. I may see what I can do with a mill file in vice. If all attempts at shaping by hand fail, then the sander is an option. Regardless, I'll remove the 16* factory edge and go back with something around 19 or 20* since these knives are worse than the Classics about chipping. After all it's a paring knife and will be used in hand and seldom on a board- I don't see the need for an incredibly thin edge.

It should be coming in the mail in a week or so. I'll let you guys know how it goes.

jules · « **Reply #6 on:** 20 Jul 2020, 01:24 am »

I don't think this is going to go down well but I'd suggest you don't bother with it.

I haven't followed the legal challenge but I own one Japanese knife that has exactly the same problem. The chips aren't as big but I was surprised that they happened at all. I've used knives professionally for many years. I'm careful with them and only use them on substances that they are designed/suited to.

Just as a personal view, super hard edges are a pain. They're difficult to sharpen, lack feel and don't out-perform blades that use slightly less brittle materials.

S Clark · « **Reply #7 on:** 20 Jul 2020, 03:46 am »

Jules, your point is well taken, and absolutely this is a project that really isn't worth the effort... but I'm really doing it for a lark. I've only got about $35 in it to my door, so if I can't make it right, it's no big deal. I kinda like bringing stuff back from the dead... Last month I rebuilt an impact wrench from the 1950's, and then a heavy duty Hitachi corded drill that needed a switch and brushes. All stuff that cost about $15-20 (before spending more than that in parts).

I've never been in a pro kitchen, so I'm sure you know when you say hard steels are a PITA. But I'm not sure that super hard edges are that hard to sharpen. I've got a couple of knives made from HAP 40 steel that is up in the ridiculous high Rockwell range... but with an EdgePro and time you can make it like a razor blade. However, I'm sure you are right that a pro can't spend the time messing with finicky steel. And I'd not want to build an edge from scratch on them by hand.
If this turns out to be a bust, it's just one of those "Oh, well" projects... sort of like when I rewired a tonearm. I pulled it off, but I'll never do it again.

Rob Babcock · « **Reply #8 on:** 20 Jul 2020, 04:52 am »

Yikes! That's a pretty big chip!

Just saw it (got back yesterday from a week-long camping trip in the Nez Perce Forest in Idaho). Obviously you can only take off steel, not add it back, so anything you do will alter the profile a lot. The repair will leave the bevel up in the suminigashi too which creates a feeling of drag while cutting. The two main ways to go would be to regrind it into a small knife with the same profile or keep most of your repairs in and ahead of the chip resulting in a very different shape.

Shun has a pretty good warranty and may replace it. If they don't they will probably "repair" it. A coworker of mine went that route. If it was VG-10 I'd probably throw it away but those SG-2 & R2 knives are spendy!

I certainly wouldn't do it by hand with diamonds. It would work- after all, the Grand Canyon was cut by moving water!

But that's about how long it will take. No, that's a job for a belt sander/grinder. But that's gonna be a lot of grinding. I would start with a 60 grit Blaze ceramic belt and take breaks to keep it from overheating. Maybe a dunk in some cold water periodically. I have a hobbyist Kalamazoo 1x42" grinder, about $300 nowadays. A 2x72" would make the job faster but if you're going out and buying it that's a significant expense.

My approach is to use a Sharpie to draw a new bevel to guide my grinding.

jules · « **Reply #9 on:** 20 Jul 2020, 05:08 am »

Quote

I kinda like bringing stuff back from the dead... Last month I rebuilt an impact wrench from the 1950's, and then a heavy duty Hitachi corded drill that needed a switch and brushes. All stuff that cost about $15-20 (before spending more than that in parts).

I'm with you on that. I guess the knife's worth a go for fun. Keeping such a small blade cool might be your biggest problem but you've already noted that.

I ground an old paring knife down and converted it to scalpel shape ... quite useful for some jobs

Looking forward to your results.

S Clark · « **Reply #10 on:** 20 Jul 2020, 05:13 am »

Quote from: Rob Babcock on 20 Jul 2020, 04:52 am

... The repair will leave the bevel up in the suminigashi too which creates a feeling of drag while cutting...And this is a real concern. I don't know if the SG2 core goes all the way up the blade, or if it's an insert upon forging. It may be the thinning suminigashi exposes-- more of the soft cladding. The hope is that thinning could remove 1/4" of cladding to expose more SG2.

Shun has a pretty good warranty and may replace it. If they don't they will probably "repair" it. A coworker of mine went that route. If it was VG-10 I'd probably throw it away but those SG-2 & R2 knives are spendy! This the wisest choice, and what I should do.

My approach is to use a Sharpie to draw a new bevel to guide my grinding. Yep, I've seen this done, it's easy, and it works.

Rob Babcock · « **Reply #11 on:** 20 Jul 2020, 05:35 am »

It's an expensive enough knife that I'd contact Kershaw USA. How did you do that? The damage I mean? In my mind that's a flaw in the knife. My coworker hit a bone in a chunk of lamb he thought was boneless. It seems pretty fragile unless you were really abusing it (not saying you were).

The hagane probably goes almost all the way to the spine. But that's a lot of metal to grind, especially SG2 or R2.

S Clark · « **Reply #12 on:** 20 Jul 2020, 12:14 pm »

I may call the company to ask their advice, but I'd have to tell them that I bought the knife as it is as a project. I've only got 35 bucks in it--no idea how it got damaged. Lot of these knives have been showing up on ebay recently. I picked up a Shun classic 8" gyuto with the very end of the tip missing a couple of weeks ago. It was an easy fix, and the plan is to give it to my daughter. This one won't be an easy fix.

S Clark · « **Reply #13 on:** 24 Jul 2020, 06:56 pm »

The Shun Kaji paring knife came in today. Put it on 140 Atoma Edge Pro plate, and realized I was going to be all day... so out to the garage and my very old Craftman table belt sander, left the rather worn out belt on it, filled a bucket of water to cool with, and 5 minutes later the chip is out and the knife reshaped. Easy peasy. Now, thinning and sharpening... that was another hour or more. I put way too many scratches in the pretty Damascus cladding, but it's sharp up to 8K and .5micron stropped after that. I'll get pics up as soon as I can figure out transferring from a phone.

S Clark · « **Reply #14 on:** 24 Jul 2020, 08:53 pm »

Aha!

Rob Babcock · « **Reply #15 on:** 25 Jul 2020, 01:12 am »

Very nice work!

With a chip that large the only real option is to decide what kind of knife to make out of it.

I'd say you did a fine job!

Rob Babcock · « **Reply #16 on:** 25 Jul 2020, 01:14 am »

BTW, an Atoma is pretty fast for what it is but vs a belt grinder it's the difference between a fast horse and a slow spaceship.

S Clark · « **Reply #17 on:** 25 Jul 2020, 01:54 am »

Thanks, Rob. It turned out about as good as I could hope for... a usable knife with good steel for the price of a reissue l.p. I'd like to thin it more later down the road, and maybe try to polish out some of those scratches up in the cladding. Don't know how they got there as I thought I was being pretty careful, but there's more than a few.

jules · « **Reply #18 on:** 29 Jul 2020, 07:41 am »

Well planned and executed! It could turn out to be something you reach for quite regularly.

mijostyn · « **Reply #19 on:** 29 Jul 2020, 12:36 pm »

Good work. If you want to get the scratches out and make the Damascus pattern really pop, first sand the blade with silicone carbide 600 grit with a light oil. The take the knife to a muslin wheel charged with gray compound (you can use a Dremel tool but you will not get as even a job as a 6 or 8" muslin wheel on a polisher.) Always keep the blade's edge pointed in the direction the wheel is spinning in. A polisher spins up. Grinders spin down. Many of us make polishers by simply turning a grinder around.
If you like you can finish off with rouge and for an even finer shine you can go to white (diamond) compound. After buffing you will have to re establish the edge
A word about Japanese tools. The Japanese layer their blades for a reason. The cutting edge or central layer is made from a variety of metals that can be hardened to upwards of Rockwell 65. So hard that the knife would easily break under minimal pressure. To prevent this the blade or tool is forge laminated to a soft low carbon steel or Kamaji (wrought iron preferable from very old ship anchor chains!) This supports the blade to keep it from snapping. If a tool or blade chips like this one the Japanese would simply say that the blade was not respected. You can not use a Japanese blade like a western one. Western blade are hardened to Rockwell 58 or so. They are much tougher but will not get as sharp or hold their edge as long. The Japanese want a sharp long lasting edge. If an edge is too brittle which can happen the Japanese will put the blade out on their roofs on a hot sunny day:)