What produces those marks on the bladeface of those knives? Manufacturing question

[mhpr262]

This afternoon I cheated on the KKF and browsed the /r/chefknife subReddit. One of the threads was from a guy who had bought a cheap knife and inquired about the marks on the bladeface that looked like marks left by a tiny caterpillar track (picture here: https://www.reddit.com/r/chefknives...iba_to_practice_sharpening/eep8b42/?context=3 )

I had seen those mark before, on the bladeface of my KIWI knives, also very cheaply made blades. They didnt look like they were left by any grinding device I know. I therefore suspected the taper toward the edge on those knives is produced by pressing/squashing the blade between two super powerful gearwheels and it is the teeth on those gearwheels that leave those marks.

That method would be more expensive for small production runs because of the upfront cost for the machinery but cheaper for extremely large numbers of knives because it could work quicker and at the same time almost without wear and tear on your tools.

Does anybody know enough about industrial style knife manufacturing to explain what leaves those marks and who can tell me if my guess is correct?

 

[Kippington]

Some kind of milling machine for sure.

 

[panda]

Even my Hiromoto honyaki has those marks!!

 

[JBroida]

its a type of cnc used for grinding knives... often used in rough grinding, but in less expensive knives, like the one on reddit, they barely finish afterwards.

 

[mhpr262]

its a type of cnc used for grinding knives... often used in rough grinding, but in less expensive knives, like the one on reddit, they barely finish afterwards.

Do you have a pic of the milling tool that leaves such marks? I have no idea what it would look like.

 

[JBroida]

they are generally in an enclosure, so they just look like an ambiguously large machine... the grinding part is usually not visible

 

[Dan P.]

I'd say those look like very rough glazing marks, produced manually on a glazing wheel. Or grinding marks from some other kind of very badly dressed abrasive wheel.
I'm happy to defer to the greater knowledge of others, but I don't know if anyone would take the time to program a milling machine to grind what appears to be quite a complex path, and then do it wobbly.

 

[Nemo]

Even my Hiromoto honyaki has those marks!!

Same on mine

 

[Michi]

The ura on the very cheap yanagiba I bought years ago looked like that.

 

[alterwisser]

I’m not sure these are milling cutter marks. For sure not facemill like the one in the video above .... it would have to be a smaller milling cutter like an end mill, thread mill or similar.

But I also highly doubt that it’s a milling cutter at all, especially not for a cheap knife. Not worth the time and effort to make these on a CNC, I think....

Then again, ist the guy from Nyatiblades trying to make mid tier production knifes on a CNC machine? (Fiftyblades?)

 

[milkbaby]

North Arm Knives starts with their blades milled out by CNC. You can see some of the lines left on the blade face:

 

[Kippington]

North Arm Knives starts with their blades milled out by CNC. You can see some of the lines left on the blade face:

I-is that a small board or a large paring knife?
I mean... the potatoes should help, but they only make me question it more!

 

[Nemo]

I-is that a small board or a large paring knife?
I mean... the potatoes should help, but they only make me question it more!

270mm paring. Two handed handle. Giant Tasmanian spuds. [emoji16]

 

[merlijny2k]

I'd say those look like very rough glazing marks, produced manually on a glazing wheel. Or grinding marks from some other kind of very badly dressed abrasive wheel.
I'm happy to defer to the greater knowledge of others, but I don't know if anyone would take the time to program a milling machine to grind what appears to be quite a complex path, and then do it wobbly.

Creating a wobbly pattern is only counterintuitive if one imagines the cutting tool moving past the blade, rather than the blade past a fixed cutting tool. Due to the curved nature of the edge an irregular pattern is created when moving the knife past the cutter at a relatively high speed.

I would say the tool is some variation of this:


Installed more like this:


This gives:

- A high speed of production
- Low tool cost: you can use a simple bar of HSS as a chisel, if you have a bigger machine you can have it autosharpen at intervals and then move the chisel forward for say .2mm after each sharpening. That way you only need manual intervention when the HSS bar runs out.

Downsides: It is not very accurate, and it produces a rough finish. The first doesn't really matter because the target 2mm behind the edge thickness is typically .8mm or so for knives made in that fashion.

The CNC motion is very simple, just the knife passing between the two cutters at a certain speed following the curve of the edge. I would bet it isn't even CNC but more of a motion that is guided by a die, like for replicating a key. This would further increase irregularity VS actual CNC since the cutters are not always perfectly perpendicular to the edge.

 

[Dan P.]

Creating a wobbly pattern is only counterintuitive if one imagines the cutting tool moving past the blade, rather than the blade past a fixed cutting tool. Due to the curved nature of the edge an irregular pattern is created when moving the knife past the cutter at a relatively high speed.

I would say the tool is some variation of this:


Installed more like this:


This gives:

- A high speed of production
- Low tool cost: you can use a simple bar of HSS as a chisel, if you have a bigger machine you can have it autosharpen at intervals and then move the chisel forward for say .2mm after each sharpening. That way you only need manual intervention when the HSS bar runs out.

Downsides: It is not very accurate, and it produces a rough finish. The first doesn't really matter because the target 2mm behind the edge thickness is typically .8mm or so for knives made in that fashion.

The CNC motion is very simple, just the knife passing between the two cutters at a certain speed following the curve of the edge. I would bet it isn't even CNC but more of a motion that is guided by a die, like for replicating a key. This would further increase irregularity VS actual CNC since the cutters are not always perfectly perpendicular to the edge.

Could be, but you could produce that finish manually in well under 10 seconds, no programming necessary!