CNC sharpening

[220-9er]

A CNC program follows a very specifically defined shape and would work well on brand new knives that are the exact (within thousandths anyway) same dimensions.
Knives that are returned by the owners for resharpening can vary dimentionally, depending on the wear and skills of those that have resharpened or touched up the blade since it left the factory. That's why manually resharpening is the only realistic way to handle that process.
The best way, as most here probably know, is to invest in at least a modestly capable sharpening system of your own and learn how to use it correctly. It's doesn't require rocket science to be reasonably competent in the required skills to keep your knife sharp. That way you can do it as much or as little as you like and keep all your knives in your home sharp without having to ship and wait.

 

[Glenn Goodlett]

There are CNC machines that sharpen end mills. I see no reason a CNC machine designed to resharpen knives could not do a great job at it. With automated probing wear is not really a factor. The problem is that the machine would cost $300K and need an operator that costs $200K a year, as opposed to a guy on a belt grinder could do an adequate job for a lot less money and probably get more production.

 

[Ilikesharpstuff]

There are CNC machines that sharpen end mills. I see no reason a CNC machine designed to resharpen knives could not do a great job at it. With automated probing wear is not really a factor. The problem is that the machine would cost $300K and need an operator that costs $200K a year, as opposed to a guy on a belt grinder could do an adequate job for a lot less money and probably get more production.

PLEASE message me the details about any shop paying an operator $200k/year.

 

[rlewpolar]

PLEASE message me the details about any shop paying an operator $200k/year.

In an Asian country (or any other country) where wages are way below US and Western Europe countries, I bet you could make the economics works.

 

[Glenn Goodlett]

PLEASE message me the details about any shop paying an operator $200k/year.

That's operator costs, not operator pay. Nevertheless, I think the guy that made the video makes more than $200K.

 

[The Mastiff]

Spyderco is using CNC controlled sharpening arms for at least some of their knives. My experience with their edges is excellent and always has been but the new ones are pretty amazing.

 

[Another Shepherd]

Out of the 6 Cold Steel knives that I have checked with a laser goniometer, 4 had wildly unequal edge angles.

I have checked 10 Cold Steel knives now, including two different Ultimate Hunters (my favorite). Most were right out of the box, none had been resharpened. All were quite sharp except for the Mini Tac Bowie, which had an average BESS score of 243 (which is not bad out of the box) and the AK-47 with an average BESS score of 377, which is rather dull because it had been used a lot, but it still had a nice V-shaped secondary bevel; I should get around to sharpening it.

Numbers like W:X-Y:Z mean:
W = Left secondary (edge) bevel angle
X = Right secondary (edge) bevel angle
Y = Left primary bevel angle
Z = Right primary bevel angle
The measurements for each knife were done at one position along the edge. I rarely see much variation along the edge except in pronounced bellies and junk knives. The numbers are probably accurate to within one degree.

The SR1 Lite had convex secondary bevels with angles ranging from 20 to 34 degrees on the left side and from 19 to 34 degrees on the right side. It had never been used except for making BESS measurements.

It is surprising that three knives had secondary bevel angles of 11 and 19 degrees. That could just be a coincidence, but I have to wonder if some machine was out of adjustment. The Recon 1 Tanto is a recent purchase. The other two were from 3 or 4 years ago.

AK-47                       CPM-3V     19:21-6:6             
Finn Wolf                   AUS-8A     11:11-0:0             
Mini Tac Bowie (Neck)       8Cr13MoV   20:16-4:4             
Recon 1                     CPM-S35VN  16:24-4:4             
Recon 1 (Tanto)             CPM-S35VN  11:19-3:3             
SR1 Lite                    8Cr13MoV   (20,34):(19,34)-8:6 Convex secondary bevel   
Tuff Lite                   AUS-8A     11:19-4:4
Ultimate Hunter @A          CPM-S35VN  18:18-4:4             
Ultimate Hunter @B          CPM-S35VN  11:19-4:4             
XL Voyager Clip Point       AUS-10A    15:19-3:3

 

[rlewpolar]

I have checked 10 Cold Steel knives now, including two different Ultimate Hunters (my favorite). Most were right out of the box, none had been resharpened. All were quite sharp except for the Mini Tac Bowie, which had an average BESS score of 243 (which is not bad out of the box) and the AK-47 with an average BESS score of 377, which is rather dull because it had been used a lot, but it still had a nice V-shaped secondary bevel; I should get around to sharpening it.

Numbers like W:X-Y:Z mean:
W = Left secondary (edge) bevel angle
X = Right secondary (edge) bevel angle
Y = Left primary bevel angle
Z = Right primary bevel angle
The measurements for each knife were done at one position along the edge. I rarely see much variation along the edge except in pronounced bellies and junk knives. The numbers are probably accurate to within one degree.

The SR1 Lite had convex secondary bevels with angles ranging from 20 to 34 degrees on the left side and from 19 to 34 degrees on the right side. It had never been used except for making BESS measurements.

It is surprising that three knives had secondary bevel angles of 11 and 19 degrees. That could just be a coincidence, but I have to wonder if some machine was out of adjustment. The Recon 1 Tanto is a recent purchase. The other two were from 3 or 4 years ago.

AK-47                       CPM-3V     19:21-6:6            
Finn Wolf                   AUS-8A     11:11-0:0            
Mini Tac Bowie (Neck)       8Cr13MoV   20:16-4:4            
Recon 1                     CPM-S35VN  16:24-4:4            
Recon 1 (Tanto)             CPM-S35VN  11:19-3:3            
SR1 Lite                    8Cr13MoV   (20,34):(19,34)-8:6 Convex secondary bevel  
Tuff Lite                   AUS-8A     11:19-4:4
Ultimate Hunter @A          CPM-S35VN  18:18-4:4            
Ultimate Hunter @B          CPM-S35VN  11:19-4:4            
XL Voyager Clip Point       AUS-10A    15:19-3:3

Good info, thanks. I’m curious, what laser goniometer are you using. I’ve been kicking around the idea of getting one.

Regarding those different edge angles, that’s disappointing, especially if these were done on a CNC machine . Kind of defeats the purpose

 

[Another Shepherd]

Good info, thanks. I’m curious, what laser goniometer are you using. I’ve been kicking around the idea of getting one.

I have two goniometers from Gritomatic. The cheap one is good for scanning along the whole edge to look for weird spots. The expensive one with magnets is easier to use to make a careful measurement at one spot along the edge.

It is not always easy to interpret the laser reflection pattern, but there is a good Youtube video by our friend from Leading Edge:

Asymmetric bevels are pretty common in many brands. It's important to know about them when you are using a guided-angle sharpener where you can flip the knife over without changing the angle, because then you will have to reprofile one or both sides. Or if you use a Wicked Edge where you can set different angles for the two sides, the goniometer will tell you what settings to use.

If you always sharpen at certain angles, such as 15 or 20 DPS, then you do not have to write down which angle you used for every knife you've sharpened, because the goniometer will tell immediately what angle it is. I've seen a lot of new knives that I think have a convex microbevel, but I'm not sure about that. The goniometer will also tell you immediately if you have a convex secondary bevel, and you can also see if the primary bevel is concave.

 

[rlewpolar]

I have two goniometers from Gritomatic. The cheap one is good for scanning along the whole edge to look for weird spots. The expensive one with magnets is easier to use to make a careful measurement at one spot along the edge.

It is not always easy to interpret the laser reflection pattern, but there is a good Youtube video by our friend from Leading Edge:

Asymmetric bevels are pretty common in many brands. It's important to know about them when you are using a guided-angle sharpener where you can flip the knife over without changing the angle, because then you will have to reprofile one or both sides. Or if you use a Wicked Edge where you can set different angles for the two sides, the goniometer will tell you what settings to use.

If you always sharpen at certain angles, such as 15 or 20 DPS, then you do not have to write down which angle you used for every knife you've sharpened, because the goniometer will tell immediately what angle it is. I've seen a lot of new knives that I think have a convex microbevel, but I'm not sure about that. The goniometer will also tell you immediately if you have a convex secondary bevel, and you can also see if the primary bevel is concave.

I actually do sharpen usually at 15 or 20 degrees and my thought was to use the goniometer initially before sharpening to see what the factory edge was and sharpen the angle that is closest to the factory edge. Is a goniometer a valid use for this purpose or is it overkill?

 

[Another Shepherd]

I actually do sharpen usually at 15 or 20 degrees and my thought was to use the goniometer initially before sharpening to see what the factory edge was and sharpen the angle that is closest to the factory edge. Is a goniometer a valid use for this purpose or is it overkill?

That is an excellent use for a goniometer. That would take maybe 30 seconds. If you used a marker in the conventional way to find the angle, that could take a few minutes, or maybe more if it is a really wonky grind. If the bevel is convex, the goniometer will quickly tell you a lot more than the marker method. If you do a lot of sharpening, the goniometer will save you a lot of time in the long run.

 

[EngrSorenson]

There are CNC machines that sharpen end mills. I see no reason a CNC machine designed to resharpen knives could not do a great job at it. With automated probing wear is not really a factor. The problem is that the machine would cost $300K and need an operator that costs $200K a year, as opposed to a guy on a belt grinder could do an adequate job for a lot less money and probably get more production.

Sharpening an end mill is relatively easy compared to a knife. Axisymmetric, and the geometry is much easier to describe to a computer.

As you said, it can be done, but I shudder to think how much time and money it’d take to get consistent results.

 

[marrenmiller]

I've probably had a dozen cold steel knives, and I haven't seen particularly great edges on any of them, with widely varying edge angles from side to side and model to model. I'm convinced that they sharpen by hand on a grinder.

The only major production OEM that I know of using robotic sharpening is Spyderco on their Golden knives. Even their machine puts out duds, but generally it's fairly consistent along the edge on each side.