New microscope, different steels, hypotheses?

[RustyIron]

Hey, kids.
Early on when I decided to give more effort to sharpening knives, I found that looking at edges under magnification could tell me a lot and point me in a better direction. I have a 60x loupe that I like for most work, and it's just right. I also have a 120x that is fun on occasion, but it isn't as useful. Recently I spotted one of those 250x USB microscopes that can be plugged into a computer and I couldn't resist. The clarity isn't really that great, but I can view larger areas, and I can provide lighting that accentuates detail. Overall, I've blown forty bucks on a lot dumber things.

After touching up a couple knives yesterday and then viewing the edges under magnification, I spotted some interesting phenomena. Following are three pics, but I'm mostly interested in opinions on the last shot. I'm using an EdgePro Professional, and the stones are the same for all the pictures: 1k Nubatama Platinum, 3k Nubatama Platinum, 5k Shapton, chunk of wood with old 1 micron CBN to strop.

This first shot is just a baseline to show what I'm doing. It's a knife from the kitchen with an unknown stainless that I've had for 30 years. I took it to 3k, then gave it another quarter degree of angle, a few strokes with the 5k, and then the strop. The pic makes sense to me: scratches along the bevel, then polishing out near the edge as I increased the angle. This is just a quickie sharpening job to put a usable edge on the knife, it wasn't intended to be a top-notch job. But you can see that I can make the edge relatively flat.

This next shot is another example, but I don't understand it exactly. I've seen this phenomenon since I got the knife. The blade is Maxamet. No matter how I sharpen it, I seem to get a matte finish at the back and front of the edge, but the middle is shiny and a more polished look. It appears to be flat. The edge is never as sharp as some of my other work, but it's not a slouch. You don't want to accidentally touch it, or it might shave off a thin layer of skin. I'm happy with the edges I get on this knife, but am sharing the picture because it might be related to the next picture.

This last shot is really the one I want to ask about. It's pretty sharp, and I was pleased with the edge. Then I put it under the scope and I've found areas that tell me I need to up my game. I gave this blade the same progression of stones as the previous two pictures, but this one is S30V. You'll see the scratches near the back and the front of the edge. In the middle, you'll see how it's polished out much nicer. That's how I intended the whole width to be.

My first thought is that I need to quit being a slob and start giving more time with each stone. Fair enough. But why is it polishing out in the middle? It would almost seem that I'm being sloppy on the coarser stones, rocking and creating a convex edge. Then with the finer stones I'm becoming more precise. I don't really buy that idea, however. My workmanship should be the same regardless of the grit of the stone.

Is it possible that on the coarser stones, there is a little slurry that is getting dragged under the blade, creating some convexity? Maybe I should be doing all leading edge strokes. Or maybe just trailing edge strokes. Or keep everything cleaner.

I could easily overcome this, sort of like in the first picture on the unknown stainless. If I give a quarter degree of angle with every step up in grit, then I'd be sure to be concentrating on the true edge, but creating a convex edge. That seems more like a hack, though, and I'd prefer to keep everything as flat as possible. Thoughts?

Thanks.

 

[sickpuppy1]

I'm going to go out on a limb here, since you say they cut good regardless of the look, and say stone thickness. If you were to use a micrometer on your stone you may find that they a slightly different thickness and therefore a slightly different angle. maybe only a .001 or two. this could equate to 20/19.5 or 20.5 etc. Easiest way to see, providing you used a digital angle gauge is to set up you first stone to say 20 deg, then immediately go to next stone and then third stone and see what the angle is for each. Some guys use a thickness compensator (me included) and some will measure the angle of each stone. Check it and see. takes a few minutes only.

 

[Diemaker]

For your third photo problem that is not stone thickness, that is movement of the blade while sharpening. I have a microscope and saw it recently in my own work. I recently finished sharpening, second try, a new Maxamet Spyderco and saw this too. Keeping your knife stable is critical to proper grit progressions. Stone thickness is important but I think there needs to be more than .01" difference in thickness for it to matter, less than that and I haven't noticed any problems.

Second photo, I am going to say you need to try diamond on your Maxamet, nothing else really works, except maybe CBN.

First photo, if you increase the magnification I will bet you will see a lot of microchipping from not removing enough steel when sharpening. I see this on my Henkels Santoku when I do the same.

 

[sickpuppy1]

ya know, that makes sense also. I sometimes forget about blade movement, as I use a Hapstone M2, which has a small adjustable plate that you set up to hold the tip of the blade. Wont bend over like that. Diemaker probably hit it right on the head. He has way more experience on an Edge Pro than I do.

 

[RustyIron]

Thanks for your guidance, gents.

For your third photo problem that is not stone thickness, that is movement of the blade while sharpening.

Entirely possible. I'll keep that in mind in the future and see what happens.

Second photo, I am going to say you need to try diamond on your Maxamet, nothing else really works, except maybe CBN.

That's been on my mind. I tried some cheap diamond plates on the Maxamet when I first got it, and the resulting edge looked similar to if you polished the wood on your dining room table with a chain saw. Do you make, or are involved in the production of the diamond matrix stones for Edgepro? Should I bag a couple from you, them, or someone else? I was thinking a 650 and 1100. Maybe I'd go with a 2300, but probably not the 4k. Any advice?

 

[HeavyHanded]

But why is it polishing out in the middle? It would almost seem that I'm being sloppy on the coarser stones, rocking and creating a convex edge. Then with the finer stones I'm becoming more precise. I don't really buy that idea, however. My workmanship should be the same regardless of the grit of the stone.

I made a drawing years agobto show how this happens off the coarse stones while still making visually flat bevels. The blade either has movement or the coarse stone is dished.
To counter this you should always try to work from shoulder to apex.http://imgur.com/a/mEIPzCG.jpg

 

[Diemaker]

Whoops, forgot about dished stones, not something I ever see firsthand now. I think that bevel problem is a dished stone now because the marks from the coarser stone are on both sides of the bevel. When my knife moves I see the marks on one side, so far.

RustyIron, yes I make the Matrix stones so keep in mind that I am biased. I would say you may want to have the 250 and go up from there, it really depends on what steels you have. The 650 is a little fine as your coarsest stone for "super" steels but would be good for good kitchen steels. The difference between the 2300 and 4k is the smallest, 8 vs 5 microns, but after a while I bet you will want it too. The 2300 is definitely getting to a polished edge, the keenes is noticeably better than what the 1100 will do. If you already have coarse diamond plates then you don't need the 80. If you are going to reprofile then I would suggest getting a bevel started with the 250 before using your diamond plates to protect them. The hardest thing on a coarse diamond stone is a sharp edge so you want to get a bevel started before trying to remove any metal.

I only sell Matrix stones to EP so I would suggest getting them from them. If you do make sure you get some abrasive to dress them with. 200 grit alox for the 650 and finer stones. 60 sic for the 250 but it only needs dressing if you used too much pressure.

 

[RustyIron]

To counter this you should always try to work from shoulder to apex.

Thanks. The amount of dish on any of my stones is pretty small. As I ponder blade movement along with the little bit of slop in my setup, working in one direction might reduce the effect. I'll give it a try.

 

[Mr.Wizard]

D Diemaker do you know the functional crossover point(s) from the Matrix stones to 3M diamond lapping film?

 

[HeavyHanded]

Thanks. The amount of dish on any of my stones is pretty small. As I ponder blade movement along with the little bit of slop in my setup, working in one direction might reduce the effect. I'll give it a try.

I have a homebrew guided sharpener that really seems to work best if I drop the angle a tiny bit with each progression, maybe as small as half degree.

Pressure could also play a role, guessing that more force on the coarse stones will bring out whatever flex there is in the system, revealed at the reduced pressure on the finishing stones.

Guided setups are cool, but they come with their own problems to be managed. The more precise, the more attention to detail is needed.

 

[Diemaker]

D Diemaker do you know the functional crossover point(s) from the Matrix stones to 3M diamond lapping film?

I have never used them but expect diamond tape will be much more aggressive than resin bond with the same size abrasive, kind of like a plated bond is.

 

[Mr.Wizard]

D Diemaker Pardon me but that seems like a strange assumption. I believe 3M lapping films are slurry coated with a resin bond. Should this not put them in the same family as your stones, and the polar opposite of plated diamond in terms of aggression?

 

[eKretz]

I concur with possibilities of dished stone or blade movement. You say your stones are "pretty flat" but have you actually checked them? Another possibility is that the stone surfaces are not equally parallel with the sliding rod. In other words even if they are flat they may be slightly angled, which would also cause the problems you're having if each stone is different. Check for flatness and parallelism to the backing. Quantitatively, so you have an actual measurement...

 

[Diemaker]

D Diemaker Pardon me but that seems like a strange assumption. I believe 3M lapping films are slurry coated with a resin bond. Should this not put them in the same family as your stones, and the polar opposite of plated diamond in terms of aggression?

Ok, not what I expected. Like I said, I have never used it so obviously don't know. Looks like I need to get some to play with, sounds interesting.

Looked it up on 3Ms website, wow, there are a lot of options to choose from, many different resins and diamond concentrations.

 

[HeavyHanded]

Have played with the diamond lapping films, the 3mil backing combined with the bond layer make them very uniform in terms of finish. They do a great job of surface polishing high VC steels.

The 3 mil does induce a very slight convex even on a flat plate. I used them quite a bit on my Washboard, a drop of mineral oil prevents loading better than water based release agents. If you dont nick it, a sheet can last a loong time.

 

[Mr.Wizard]

I haven't used them either, but I thought it reasonable to combine them with the Diamond Matrix stones given their construction.

 

[RustyIron]

This evening I ordered up a handful of Diemaker's diamond matrix stones from EdgePro. Decided to go with 650 through 4k. As is the case with any new stone, I'm eager to try them, and will probably not be able to bring myself to work with anything else before their arrival.

You guys were talking about lapping film. I've only dabbled with that, in about the 6k realm. My challenge was that it was really easy to scratch the film. I didn't know if I should decrease the angle just a hair, or carefully unweight the arm so there was less pressure. I lost interest and did something else.

 

[Diemaker]

You will probably miss the 250 more than like the 4k but glad to hear you got a set. Use wet, keep wet while using, 10 edge trailing strokes per 3" per stone once you set the bevel, light pressure, and a light scrub with your finger right after using before it dries. Don't worry about them turning dark, it doesn't make much difference how they work.

The fragility of the EP tapes was the inspiration for the Matrix stones. You can still nick them but it really doesn't hurt them, not good for the knife though.

 

[RustyIron]

You will probably miss the 250 more than like the 4k but glad to hear you got a set.

Thanks to all you guys for the expert guidance. I got the pile of stones because I know that if I didn't, I'd always be wondering "what if?" The new rocks arrive Thursday, but I probably won't use them on anything interesting until one of my blades needs a some touch-up. I'll take pictures.

 

[sickpuppy1]

lol, Welcome to the dark side my friend. I just now ordered a new 650 Matrix ten minutes ago. I lent it to a bud and have been trying to get it back for over a month. one excuse after another..... He owes me a BUNCH of beer...