Sharpmaker question.

[Razzle]

Yesterday, sharpening my PM2 and Millie, starting with the diamond rods, I finally figured out what a "clean apex" is! Had to take quite a bit of material off the Millie, as the factory edge was a good 75% larger on one side. Used the Sharpie all along, until I had a good idea about "hitting the edge", etc.

Now have beautiful, SHARP edges on both knives, with a nice toothy 15 degree primary bevel and a sharp 20 degree micro.

My question is, all is normal that one edge is still larger than the other, as that's the way it came from the factory, as long as the edges meet nicely at the apex, correct?

Short of removing a lot more material (spent three hours on the diamond rods already, just on the Millie), I'm golden, right?

[JD Spydo]

What you're talking about is what John Juranitch refers to as primary and secondary bevels. He explains it in detail in his great book on sharpening entitled "The Razor Edge Book Of Sharpening" and you can get them from Razor Edge Systems out of Ely, Minnesota.

The Spyderco 204 Sharpmaker makes that process so very much easier than just about any other sharpening tool I know of. I'm assuming that both of the knives you mentioned probably have S30V blade steel???

You might also check out the ultra-fine stones you can buy extra for the 204 Sharpmaker. To me they are worth their weight in high grade Gold.

It sounds to me like you are learning to use the 204 Sharpmaker the right way. I've yet to use the CBN rods for the 204 Sharpmaker but they are high on my list and I should have them soon.

[Razzle]

The primary bevel is still 25% "larger" on the left side of the knife, it was REALLY off from the factory.

The nice, perfectly even scratch marks from the diamond rods are worth their weight in gold to me, I find it even prettier than a mirror edge!

[Cliff Stamp]

My question is, all is normal that one edge is still larger than the other, as that's the way it came from the factory, as long as the edges meet nicely at the apex, correct?

It is not uncommon. If the blade bevels are not perfectly even then when you grind the edge bevels at the same angle then they will be different in width. It can be adjusted by grinding down the blade on the other side, but that would be a fair amount of work on the Sharpmaker. You could also grind the narrow side until it evens out, however that is a decent waste of steel unless the look of it really bothers you.

[Razzle]

Exactly as I thought, Cliff, thanks for chiming in.

The left side is still about 25% larger, much better than the 75% I started with.... I can live with that.

Another question? When sharpening my M4 Gayle Bradley, if I go from the diamonds at 30 degrees to the brown rods at 40 degrees, the edge chips badly while sharpening. Seems to do much better if I stick with the diamonds at 40 degrees and stop there?

Is this characteristic of the M4 steel, or?

[Cliff Stamp]

Is this characteristic of the M4 steel, or?

When you jump from the 30 to the 40 the pressure on the steel explodes because the contact area gets so small. Pressure is force/area. When you are working on the edge bevel, the pressure is going to be similar to :

-5 lbs / (1/32" * 1/2") ~=300 psi

Assuming you apply 5 lbs, which unless you are trying to be very light is likely close to the force you are using. Just press on a bathroom scale, it is very easy to exert 5 lbs.

However when you jump to the 20 dps slots the contact area isn't the edge bevel (typically 1/32" wide), it is the very apex which is actually going to be on the scale of ~1/1000" . This means the pressure will explode up to :

-5 lbs / (1/1000 * 1/2) = 10, 000 psi

This would be like if you pressed down on the 15 dps settings with 150 lbs. If you did that it is likely that the knife would be at risk of damage. In short, the solution is just to go very light when you switch to the 20 dps setting.

[jabba359]

When you jump from the 30 to the 40 the pressure on the steel explodes because the contact area gets so small. Pressure is force/area. When you are working on the edge bevel, the pressure is going to be similar to :

-5 lbs / (1/32" * 1/2") ~=300 psi

Assuming you apply 5 lbs, which unless you are trying to be very light is likely close to the force you are using. Just press on a bathroom scale, it is very easy to exert 5 lbs.

However when you jump to the 20 dps slots the contact area isn't the edge bevel (typically 1/32" wide), it is the very apex which is actually going to be on the scale of ~1/1000" . This means the pressure will explode up to :

-5 lbs / (1/1000 * 1/2) = 10, 000 psi

This would be like if you pressed down on the 15 dps settings with 150 lbs. If you did that it is likely that the knife would be at risk of damage. In short, the solution is just to go very light when you switch to the 20 dps setting.

Very good explanation on pressure and why very light strokes are needed when sharpening the apex. It's pretty crazy how quickly pressure goes up when you're working on such small scales!

[Cliff Stamp]

Yeah, it is why the corners give people fits especially with steels like ZDP-189. If you saw someone for example take two hands and rake the knife down as hard as they can on the flats it would be obvious that is likely to cause problems with the edge deforming/chipping as much as abrading. However just look at the contact area on the corners. There is no difference pressure wise between increasing the force or reducing the area, hence the corners can do wicked damage to an edge under even low forces.

[Razzle]

Very good explanation, Cliff, explains almost exactly what I was doing wrong.

The S30V seems much more tolerant of my hamfistedness than the M4 does.

[Cliff Stamp]

The S30V seems much more tolerant of my hamfistedness than the M4 does.

It is likely the M4 is much harder, the main issue is going to be ductility and that tends to decrease with hardness (though there are other factors). It could also be the edge angle/thickness.

This is why for example people using Japanese knives warn about sharpening on rods. If you take one of those very thin ground blades to the Sharpmaker and use the corner then you can literally see the edge bending over the corner of the rod. If you take one of them and press down hard and rake it down then you can chip out the entire length of the edge of the knife.

[Razzle]

So the harder the steel the MORE time its going to take on the Sharpmaker, as I have to use less pressure than say with S30V, correct?

I have to be more subtle on the diamond rods with the M4......beginning to see why there are so many fans of VG10, me included!

[Cliff Stamp]

The harder and the higher the alloy, the more you see elements like Vanadium, Tungsten, Molybdenum, Chromium, especially if it is combined with a very high carbon level.

What I would suggest is to pick a knife you don't mind wearing out, and sharpen it only on the diamond rods and just get very good at applying just enough force to make them cut.

When you can get nice edges off of the very coarse stones it will make it much easier to refine on the finer stones. Have a look at the edge off of the stone in this video, it is a really coarse 36 grit stone (the diamond rods are 400 grit) :

https://youtu.be/AQnhNfWIj7Q

When you get really comfortable with the diamond rods and can use them with a very light touch you can get to the point you can sharpen a knife in easily 30-60 seconds. The procedure will be very similar to :

-grind the edge on the diamonds rods, 25-50 passes at 15 degrees
-grind the apex on the medium (or fine rods, depending on the sharpness you want), 5-10 passes at 20 degrees

[Razzle]

Once a good apex has been initially established, you're saying.

The above can now be easily done on my PM2 and Millie, but first establishing a good edge took literally hours on each knife.... especially the Millie, as it took that long just to start taking off Sharpie at the apex.

I must say, it's an incredible feeling to finally reach this point, as both knives have gorgeous edges, are screaming sharp and after all this sweat equity, I am very bonded to each of them.

Will retackle the M4 GB this weekend.... gently.

[Cliff Stamp]

If it is taking you that long you might want to scan through this :

- viewtopic.php?t=66998#p1005054" onclick="window.open(this.href);return false;

I wrote a post awhile ago on how to significantly decrease grinding time when sharpening knives and you have to change the edge angle and it also works if the angle has to be evened out.

[Razzle]

Makes sense, I was already doing the up and down grind.

Another question.. I'm not overly concerned about slightly rounding tips on my every day user knives, as I rarely find any need for ultimate "piercing" sharpness. But on those blades that I'd rather keep pristine, how does one not round tips using the SM?

And, thanks so much for your time, I'm learning a bunch!

[Cliff Stamp]

But on those blades that I'd rather keep pristine, how does one not round tips using the SM?

The main reason this happens is that people pull the knife off the rod and this rakes the tip right across and into the sides of the stone.

[WorkingEdge]

Cliff. Some of your posts add so much to my understanding. This one will immediately affect how I sharpen. Love it!

Is this characteristic of the M4 steel, or?

When you jump from the 30 to the 40 the pressure on the steel explodes because the contact area gets so small. Pressure is force/area. When you are working on the edge bevel, the pressure is going to be similar to :

-5 lbs / (1/32" * 1/2") ~=300 psi

Assuming you apply 5 lbs, which unless you are trying to be very light is likely close to the force you are using. Just press on a bathroom scale, it is very easy to exert 5 lbs.

However when you jump to the 20 dps slots the contact area isn't the edge bevel (typically 1/32" wide), it is the very apex which is actually going to be on the scale of ~1/1000" . This means the pressure will explode up to :

-5 lbs / (1/1000 * 1/2) = 10, 000 psi

This would be like if you pressed down on the 15 dps settings with 150 lbs. If you did that it is likely that the knife would be at risk of damage. In short, the solution is just to go very light when you switch to the 20 dps setting.

[Cliff Stamp]

Pressure is really critical with abrasives, most people just think about the force. If you were to take a knife and press down with a lot of force almost everyone watching you would note you are likely to cause damage. However it is very easy due to the curvature of knives for the area of contact to be very small and this will also generate very large pressures, just like if you had applied a lot of force. The next time you sharpen, have a look at what happens to the contact area as you sharpen through the tip. Watch how much of the edge typically contacts the stone, similar when you do recurves.

[Surfingringo]

Exactly as I thought, Cliff, thanks for chiming in.

The left side is still about 25% larger, much better than the 75% I started with.... I can live with that.

Another question? When sharpening my M4 Gayle Bradley, if I go from the diamonds at 30 degrees to the brown rods at 40 degrees, the edge chips badly while sharpening. Seems to do much better if I stick with the diamonds at 40 degrees and stop there?

Is this characteristic of the M4 steel, or?

I have a couple of knives in m4 that are daily users and see a lot of sharpening. I typically sharpen them just as you have described (including the medium rod microbevel) and have never had any chipping issue. Cliff is probably right about the pressure being the culprit. Typically after I've got a clean, sharp apex it only takes 8-10 (or even less) very light strokes to put a razor sharp microbevel on it. (I always use the FLATS of the rods for this) From there I just keep resharpening the microbevel until it starts to overtake the primary and sharpenings start to take too long. If you don't "oversharpen" your microbevel and remove more steel than necessary, you will be able to get in way more sharpenings before a reprofile is needed.

Glad you had the "apex epiphany". That's pretty much the whole game so it's all smooth sailing from there. :-)

[Razzle]

You were my initial instructor, gringo!

I am just using too much pressure.