Will cutting a food releasing groove in a knife with a water cooled dental handpiece damage a knife?

[ditomura]

I’ve been unable to get one of those hook grind/B grind etc. knives for food release. So I was thinking of modifying one of my knives. I have access to high speed dental handpieces. I can increase the water and adjust the speed to prevent overheating. I have a variety of diamond bits used to make clean cuts in teeth. I was wondering if this would work. I might try it out on a cheap knife. What do you think?

 

[Jovidah]

Maybe try it on a Shigefusa or a Kato and document your progress? Should make for a fun thread...

 

[ethompson]

What’s the minimum speed? I can tell you from experience that you can pretty easily cook the steel and ruin the HT with a dremel at min speed and similar attachments even under running water

 

[dabes]

The B grind is more than just the fuller near the edge of the knife, the area above the fuller to near the spine is also ground and slightly sunken in.

I sometimes polish with diamond paste on felt w/ a dremel and just that can get uncomfortably hot at anything above minimum speeds.

 

[ditomura]

What’s the minimum speed? I can tell you from experience that you can pretty easily cook the steel and ruin the HT with a dremel at min speed and similar attachments even under running water

The handpiece is air driven by a compressor. The speed is variable depending on foot pressure. I don’t know what the rpm is but if it’s too low it will not cut, the bur will just stop when contacting a hard surface. So the rpm is pretty fast, I have to hear that high pitched whine to know that it will cut. Since heat isn’t good for a tooth, i was thinking that heat would be minimized when cutting a knife. I’ll use light, multiple strokes to reduce heat also. The water is constantly directed at the cutting surface.

 

[gentiscid]

Are u going to inject lidocaine to the knife before doing that? Ice pack and soft foods to be cut with the knife after procedure… lol.

Jokes apart, it’s not a good idea. Buy a Takeda for food (S grind) release. Or a decent western.

 

[nhb22]

I think this is super interesting. Sounds feasible to me. You can probably have a bucket of ice water on the side and drip the blade in as often as you need and be conservative with temperature control. There are some Hawaii based knife makers. Might be better to DM a couple of knife makers.

https://www.instagram.com/rpm_neil?igsh=OTl2d2t2eTltY2kx

 

[ethompson]

Don’t try it on a knife you really like first. Also depending on the amount of material being removed be prepared for the blade to warp as you grind.

 

[ditomura]

I’ve been fascinated with a Kippington video, where he diced a potato and the potatoes didn’t stick to the knife. I contacted him and unfortunately he’s not making the hook grinds anymore. I have a Takeda which I like but diced onions stick to the knife.

 

[nhb22]

I do agree it is not worth it, the risk or your time really…if you are a dentist, your hourly rate is probably too expensive to make this worth awhile. But I assume you want to do it for fun…

 

[ditomura]

I was thinking of using a Wusthof chef knife or an Amazon “Kasumi” gyuto to test it out.

 

[nhb22]

@Sweetlou can you try dicing some onion with that Karys cleaver? I bet it doesn’t stick much.

 

[Uncle Danny]

I REALLY have a hard time seeing you succeed without ruining the HT. I would totally be a cool thing to do, but you would have to go as slow as Barry White goes deep. Constantly focusing on temperature. Maybe a laser thermometer fixed to read the blade surface

 

[Just a DK]

Is this what retired dentists do with their time

 

[ditomura]

I do agree it is not worth it, the risk or your time really…if you are a dentist, your hourly rate is probably too expensive to make this worth awhile. But I assume you want to do it for fun…

Yeah, I thought it might be a fun experiment. I ordered a Tobias Hangler S grind bunka and I’m getting a custom made food release knife from Tim Johnson but I haven’t received them yet. I almost bought your Karys nakiri but that knife looks too nice snd my wife might get suspicious on how much I’m spending on these knives.

 

[ditomura]

The ice water is a good idea, should I also cool the knife in the fridge. Will the sudden change in temperature be bad for the knife?

 

[ethompson]

The change in temp happens so fast on thin steel it won’t matter much. Ice water dunks, running cold water, and diligent patience to only do a light pass at a time will be your friends

 

[Sweetlou]

@Sweetlou can you try dicing some onion with that Karys cleaver? I bet it doesn’t stick much.

I used it last week on onions, squash, mushrooms and garlic. It worked flawlessly.

 

[aporigine]

The handpiece is air driven by a compressor. The speed is variable depending on foot pressure. I don’t know what the rpm is but if it’s too low it will not cut, the bur will just stop when contacting a hard surface. So the rpm is pretty fast, I have to hear that high pitched whine to know that it will cut. Since heat isn’t good for a tooth, i was thinking that heat would be minimized when cutting a knife. I’ll use light, multiple strokes to reduce heat also. The water is constantly directed at the cutting surface.

Iirc those bits spin at 200k rpm.
They are optimized for ceramics (like teeth). I’m curious how they work on hard metal.

 

[aporigine]

Is this what retired dentists do with their time

they’ve got deep experience tuning choppers.

 

[ditomura]

Iirc those bits spin at 200k rpm.
They are optimized for ceramics (like teeth). I’m curious how they work on hard metal.

I’ve been able to cut off metal crowns and bridges with them but these metals are probably softer than most of the knife steels. White gold is used for corrosion resistance and other metals are added to increase the hardness. Nowadays, crowns are milled from a solid block of hardened zirconia. I’m able to cut zirconia but it takes much longer and the burs dull quicker. The hardness of a zirconia crown is 8.5 on a Mohs hardness scale. I don’t know what this equates to on a Rockwell scale.

 

[aporigine]

I’ve been able to cut off metal crowns and bridges with them but these metals are probably softer than most of the knife steels. White gold is used for corrosion resistance and other metals are added to increase the hardness. Nowadays, crowns are milled from a solid block of hardened zirconia. I’m able to cut zirconia but it takes much longer and the burs dull quicker. The hardness of a zirconia crown is 8.5 on a Mohs hardness scale. I don’t know what this equates to on a Rockwell scale.

I don’t think it’s linear.
Zirconia is also very tough for a ceramic. Not as hard as diamond, but tougher. I think cbn falls in between.

 

[James]

What’s the minimum speed? I can tell you from experience that you can pretty easily cook the steel and ruin the HT with a dremel at min speed and similar attachments even under running water

Generally about 400k rpm, but the contact area of these burs is less than 2 mm.

It might be worth a try to use carbide burs instead of diamonds. I typically use carbide burs for metal cutting and diamond for tooth and ceramic. The carbide burs mill and diamond burs abrade.

Also, fine diamonds and a lot of water work well on zirconia for me

 

[refcast]

Should be straightforward. The groove or recess doesn't need to be super deep in my tests either, when I tried doing this sort of stuff with fingerstones for food release. Try one portion of the tester knife first though. The dental tool is water cooled and I don't think it'll damage the heat treat -- if in contact with water and doesn't steam. So no steam, if there's liquid water, no damaged ht. Just don't cut yourself, etc, usual precautions. The hook grind / shinogi recess tends to work best 1-3cm from the edge, you can test or decide how you want to do it. I've broken and damaged... A lot of knives, so no big deal, have cheap beater knives if you want, too. But principles of food release are less surface in contact with the food, no wide flat surfaces on the blade, and thin enough behind the edge ... Idk why but knives seem to need to be thin there. Depends on the existing blade geometry

 

[Yoshi]

Don't think your issue will be heat. Milling freehand is unlikely going to get you a desired neat groove.

 

[Vertigo]

Just scratch up the sides of the knife on a diamond stone or a concrete block.

 

[ditomura]

Just scratch up the sides of the knife on a diamond stone or a concrete block.

I thought you were joking but this might work. Food is less likely to stick to a rough surface. I have a nakiri with a dimpled tsuchime finish but food still sticks to it. Maybe I’ll roughen up the right side of that knife with some sandpaper.

 

[Vertigo]

I thought you were joking but this might work. Food is less likely to stick to a rough surface. I have a nakiri with a dimpled tsuchime finish but food still sticks to it. Maybe I’ll roughen up the right side of that knife with some sandpaper.

Yeah, dimples and scalloping never work quite as well as just scratching the heck out of your knife.

 

[aporigine]

I thought you were joking but this might work. Food is less likely to stick to a rough surface. I have a nakiri with a dimpled tsuchime finish but food still sticks to it. Maybe I’ll roughen up the right side of that knife with some sandpaper.

This is why Shibata knives have an apparently unrefined belt finish. With his knives thin as (word), that deep-scratched finish improves food release.

 

[ditomura]

I have a 165mm Kyohei Shindo Santoku that I was thinking of modifying. This already has a hollow grind and food release is pretty good. The problem is the knife is only 2mm thick slightly above the shinogi line where I was planning to make the groove. I was thinking I could put a 1mm grove there but would that be deep enough to make a difference. I drew a blue line on the knife where I planned on cutting.