Sharpening M390 is puzzling

[scottc3]

If you're referring to some kind of fine angle adjustment gizmo, there is one available, but I don't have it yet.

I was thinking about adjusting height of clamped blade in relationship to stone holder adjuster mechanism height, so that angle adjustment could go higher or lower. Unlike both sides of a rocking ships deck, always being on the same horizontal plane no matter what side to side roll there is, some guided systems allow you to break that plane. As I have a KME, this adjustment can only be made, broken, on the stone side, by swapping the stone carrier plate upside down, allowing lower angles to be achieved. From reading, I thought EdgePro and other systems allowed other adjustments before setting the angle.

 

[Blankblank]

Blank, even a bad heat treat would take a good edge, it just wouldn't hold it.

Are you measuring stone angles when you switch stones or strops? different stones have different thickness's so the angle changes. And yeah, strops take a very light touch. Otherwise they tend to create a concave edge.

A bad heat treat can effect the steels tendency to hold on to the burr. It definitely will lead to less edge retention too, which it sounds like he is having a problem with, but it can also effect the ability to get sharp initially too because of that. Excessive retained austinite will cause this to happen, and with something like m390 I could see that happening, if made in a large enough batch, I've heard of different parts of the oven reaching different temperatures. They also might choose to quench with more cost effective methods for large batches that cool the knife slower, and not do their cryo treatment at best time for reducing retained austinite, because it will increase risks of warps or cracks during heat treating. All of this stuff together, could lead to excessive retained austinite.

This is a quote from larrin Thomas in his article testing the edge retention of different steels. In this particular part he is talking about the ease of sharpening of the steels, and before this he mentions he didn't notice much difference between them. Except the following.

The biggest differences in ease in sharpening were instead with burr removal. The only truly difficult to sharpen knife was in Rex 121, I believe this was the result of high retained austenite rather than pure wear resistance, as Rex 86 and 15V sharpened fine. Some steels which were also expected to have relatively high retained austenite like Vanax also were relatively difficult to deburr. A modified heat treatment for reduced retained austenite would be expected to lead to greater ease in sharpening, though sharpening to higher polish where the burr size is reduced would also help.

 

[Spats McGee]

Given that it is Fathers' Day, I allowed myself a little extra time doing stuff that I enjoy. Among other things, I sat down and took another run at the Valet.

https://imgur.com/a/hcC482L

I put the Valet in the clamps, and dropped the angle to 15*. I had to remove the thumb studs to sharpen at that angle. Otherwise, I would have either: (a) had to leave a section at the heel of the blade alone; or (b) grind the thumb stud down with the diamonds. Neither of those options is any good, and the studs came off without too much trouble.

Anyway, I put it on the Hap, broke out the angle cube, and got a surprise. For reasons I don't understand, there was (to my mind) a pretty big difference in the angle when I flopped the blade. IOW, when I had the knife with the handle to my left and the pointy end pointing right, I put the stone on the blade and set it at 15.0*. When I rotated the clamps so that the knife was reversed, it was at something like 14.7*. I set and reset everything a couple of times, just in case I was missing some major factor here. I found nothing and could only conclude that there is some kind of Geometry Voodoo going on that is beyond the ken of my knowledge.

Armed with that knowledge, I re-measured the angle every time I flipped the knife except for one time I forgot, but that was only a few strokes before I remembered. I sharpied the edges and went through the 200, 600, and 1K grit stones. I continued until I could no longer detect any kind of burr with a Q-Tip. Then I ran several passes through cork. So far, I am pleased with the result. It is notably sharper than I have ever gotten it.

 

[UncleBoots]

Anyway, I put it on the Hap, broke out the angle cube, and got a surprise. For reasons I don't understand, there was (to my mind) a pretty big difference in the angle when I flopped the blade. IOW, when I had the knife with the handle to my left and the pointy end pointing right, I put the stone on the blade and set it at 15.0*. When I rotated the clamps so that the knife was reversed, it was at something like 14.7*. I set and reset everything a couple of times, just in case I was missing some major factor here. I found nothing and could only conclude that there is some kind of Geometry Voodoo going on that is beyond the ken of my knowledge.

Somewhere on here, I ran into nice visual instructions about how to use all three of the screws on those clamps to avoid that asymmetry. The basic idea is that you look from the side, and use the back screw to make the clamp's hold exactly conform to the slope of the part of the knife you're gripping, so you get a flat grip that's even on both sides, instead of just pinching the knife at one point on each side.

 

[777 Edge]

Hi Spats, glad the M390 is behaving itself for you now!

If I may recommend something; for consistency and to try and avoid chasing a rabbit down a hole, it's best to always measure on one side of your knife only. The small angular difference could be anything from the knife grind to the clamps or position. The same thing goes for TSProf, Hapstone, KME, Edge Pro, Kazak, Kakbritva, Work Sharp or any of the similar type of systems. Whatever it is in every case, you'll find the same thing with most knives. Personally, I only measure with my knife facing handle to the right and I flip back to that position when changing stones and readjusting the angle for the new stone again.

If you re-measure and adjust the angle every time you flip, you could possibly end up chasing the angle too much, make a mistake or forget adjusting back when you flip back again. This could sometimes lead to a downhill spiral. A difference of 0.3 degrees from one side of the bevel to the other side it completely insignificant, but if you change the angle and forget to change it back when flipping over, you could end up missing the edge bevel in the perfect spot, due to changing the angle all the time.

Your miles may vary, but personally I find the best results by always only measuring and adjusting the angle on one side.

 

[3D Anvil]

I second what 777 Edge said. It's totally not worth driving yourself nuts over <.5°. The truth is that *many* knives, straight from the factory, are 2, 3, or even 4° off from one side to the other. It's a rare case when a factory bevel is off by less than a full degree.

 

[Spats McGee]

Good to know. I chased that rabbit and he's fast.

 

[Blankblank]

Definitely good to hear you got a good edge. Lowering the angle can make a huge difference. Especially on knives that are a bit thicker behind the edge.

There was a customer that had a wierd crkt knife that was huge, it was one of the ones that used d2 steel I believe, and a propriety lock for the blade. This thing was basically a big fat pry bar, with how thick it was, and just going off of the angle that was put on by the factory, I couldn't get it to cut anything. I could get the edge sharp (able to shave) but if you tried to cut a piece of paper or cardboard it wouldn't work. The only thing that was able to get it cutting, was to quickly pull out a coarse stone, and drop the angle quite a bit. Which because of how thick this thing was, made the bevel look pretty huge. After that the customer was happy with the results. Though as far as my opinion goes, it couldn't perform as a knife worth a damn.

Moral of the story is geometry is huge, and though that knife was an extreme example. Having a sufficiently low angle, that is still able to be supported by the strength of a given steel, is usually a big part of getting the best possible results. Along with making absolutely sure that the edge is completely deburred, and that the apex isn't being rounded over (usually not as big of a concern on a guided system) .