- Joined
- Dec 9, 2003
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- 4,817
So my chef friend was telling me one day that he had this funny idea with his coworkers of a knife that had 5 blades so it could cut a chicken katsu (japanese breaded fried chicken) fillet into pieces all in one stroke. I thought about it and I told him I think I could actually make it. So he went out and bought 5 chinese cleavers for about $8 each. Decent quality in my opinion, chinese brand, nothing fancy, good knife for the money. Not sure what metal but it said stainless steel.
I decided to design some sort of spacer system to make all 5 knives about 3/4" apart which is my ideal chicken katsu strip width. The handles were rounded and all metal so I could not just attach the handles, plus it would be too hard to hold on. So first step was to buy a grinder/cutoff wheel and cut off 4 of the 5 knife handles. This went pretty fast. I was affraid of the heat build up with this and the drilling but interestingly even though the area got red hot the blade was only barely warm to the touch near the edge of the blade.
I could not figure out an ideal spacer system or material to use so after some deliberation and time at the hardware store I decided to use a 1/4 bolt and nylon spacers. I figured that the nylon would be the best since it should be food safe (cutting board material right?), wont rust, wouldn't have any adverse reaction to food acids or other metals and because it might seal off between the blades when everything was tightened down. So I got 1/4" inside diameter nylon spacers, the unthreaded type. Then 2 bolts and 2 lock washers. This system, I figured, would also have the added benefit of allowing one to take apart the knife for cleaning rather than me having to try and devise a system that was permanent but no way to clean if food oil slipped into spaces.
So the drilling is where I had trouble. I decided to use a carbide tipped 1/4" masonry bit as I had found a masonry bit to work on another hardened blade project some time ago. Well the bit didn't do much at all. It couldn't dig in to start a hole even when I used a dremel tip to grind a shallow divet into the metal. Every different bit I tried wouldn't so much as scare the knife, a glass/tile spade bit, a conventional drill bit etc. Then I read an idea on the internet about spot annealing and one person had use a drill bit running at high speed till it heated up to soften the metal.
I took an old 1/8" (i think) carbide tipped masonry bit that was kind of eaten up and threw it into my drill press with the pulleys set to maximum speed. I then pressed the bit onto the blade with some force and after about 20 seconds or so the bit started to glow red. It made the metal immediately around the bit glow red too. As it got red I could feel the bit really start to drill through the metal and I let it go most of the way. A note of caution, the spinning bit may spread shards of red hot steel flying at you. Once red hot for a few seconds I let it cool off and then I went back and hit it with the 1/4'" bit at low speed. The metal had clearly softened and the bit ate right through. I have to say I love this method, it was pretty easy with no special tools. Again the blade never got very hot except immediately around the hole. It also did not seem to destroy the bit as I was expecting even though it was already partially eaten up. I am theorizing that maybe the carbide tip somehow is able to withstand very high temperatures and not deform when compared to the red hot steel. Maybe a conventional multipurpose drill bit would have also lost its heat treat and not actually drilled anything but just heated up the one point.
Then just bolt the whole thing together. I still have to trim off the bolt ends but the guy loves it. Heavier than I though, and I definitely would not want to get cut by that. It would turn your arm into a cut up sushi roll.
Possible problems: Even if I got the holes perfectly matching on all the blades I realized that the edges are probably hand ground and were not identical knife to knife. I managed to get them all to line up fairly close to the point that I think it will cut most foods right through without a problem, but it took a lot of time measuring and a lot of luck in the end for the edges of the 5 knives to line up from tip to back all at about the same point.
So what do you guys thing? Great educational lesson for spot annealing for me.
Photos: Sorry I didn't take any photos to illustrate the drilling process. not so good phone pics but I am sure you get the idea.
I decided to design some sort of spacer system to make all 5 knives about 3/4" apart which is my ideal chicken katsu strip width. The handles were rounded and all metal so I could not just attach the handles, plus it would be too hard to hold on. So first step was to buy a grinder/cutoff wheel and cut off 4 of the 5 knife handles. This went pretty fast. I was affraid of the heat build up with this and the drilling but interestingly even though the area got red hot the blade was only barely warm to the touch near the edge of the blade.
I could not figure out an ideal spacer system or material to use so after some deliberation and time at the hardware store I decided to use a 1/4 bolt and nylon spacers. I figured that the nylon would be the best since it should be food safe (cutting board material right?), wont rust, wouldn't have any adverse reaction to food acids or other metals and because it might seal off between the blades when everything was tightened down. So I got 1/4" inside diameter nylon spacers, the unthreaded type. Then 2 bolts and 2 lock washers. This system, I figured, would also have the added benefit of allowing one to take apart the knife for cleaning rather than me having to try and devise a system that was permanent but no way to clean if food oil slipped into spaces.
So the drilling is where I had trouble. I decided to use a carbide tipped 1/4" masonry bit as I had found a masonry bit to work on another hardened blade project some time ago. Well the bit didn't do much at all. It couldn't dig in to start a hole even when I used a dremel tip to grind a shallow divet into the metal. Every different bit I tried wouldn't so much as scare the knife, a glass/tile spade bit, a conventional drill bit etc. Then I read an idea on the internet about spot annealing and one person had use a drill bit running at high speed till it heated up to soften the metal.
I took an old 1/8" (i think) carbide tipped masonry bit that was kind of eaten up and threw it into my drill press with the pulleys set to maximum speed. I then pressed the bit onto the blade with some force and after about 20 seconds or so the bit started to glow red. It made the metal immediately around the bit glow red too. As it got red I could feel the bit really start to drill through the metal and I let it go most of the way. A note of caution, the spinning bit may spread shards of red hot steel flying at you. Once red hot for a few seconds I let it cool off and then I went back and hit it with the 1/4'" bit at low speed. The metal had clearly softened and the bit ate right through. I have to say I love this method, it was pretty easy with no special tools. Again the blade never got very hot except immediately around the hole. It also did not seem to destroy the bit as I was expecting even though it was already partially eaten up. I am theorizing that maybe the carbide tip somehow is able to withstand very high temperatures and not deform when compared to the red hot steel. Maybe a conventional multipurpose drill bit would have also lost its heat treat and not actually drilled anything but just heated up the one point.
Then just bolt the whole thing together. I still have to trim off the bolt ends but the guy loves it. Heavier than I though, and I definitely would not want to get cut by that. It would turn your arm into a cut up sushi roll.
Possible problems: Even if I got the holes perfectly matching on all the blades I realized that the edges are probably hand ground and were not identical knife to knife. I managed to get them all to line up fairly close to the point that I think it will cut most foods right through without a problem, but it took a lot of time measuring and a lot of luck in the end for the edges of the 5 knives to line up from tip to back all at about the same point.
So what do you guys thing? Great educational lesson for spot annealing for me.
Photos: Sorry I didn't take any photos to illustrate the drilling process. not so good phone pics but I am sure you get the idea.
