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Matt Todd

help sharpening

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For the life of me I just can't seem to get a sharp edge on my knives. I have watched countless videos, but I feel like I'm missing something. Does anyone have any secrets or advice? I don't feel I can in good conscience sell a knife that isn't sharp.

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What is your current process?

and how about a couple pictures of the edge geometry on the sharpest knife you have done so far...

James

Edited by James Spurgeon

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I use my 2x72 slack platen starting with a 220 jflex belt and go to 800. Then move to my Sydeco Sharpmaker. 20 passes per side and stone. Normally works. On occasion I will need another 10 passes per side.

Edited by GBrackett

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Primary variable is edge geometry rather than method used to achieve it...

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Do you use a leather strop? Leather, for me, is the difference between an acceptable edge, and a really sharp knife. I use stones until it can shave hair, but still not that great, and then stop on leather for ten minutes or so, and by then I should have a really great, hair whittling sharp edge. Also, work on edge angles, I tend to do a convex on the cutting edge, by working on thinning the area just behind the cutting edge, before doing just a few strokes on the very edge.

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I do an apple seed shaped convex grind. I strop depending on the use and need of it related to the use of the knife.

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My process is pretty basic. I set my bevel at 30 degrees on a course stone. I continue the process with the fine side of the stone. I have a strop, but whenever I use it I lose the burr. I have a honing stone, but I bought it for sharpening straight razors. Which is something else I am working on. I really don't want to use it for knives. I wonder if maybe I am using too much pressure, or I'm not working at it long enough. Sometimes I get a good burr, but its only to one side as I drag my thumb across it. I would use my belt grinder to set the bevel, but my hand is not that steady and my skill level is moderate. I don't have any really good pictures of my last knife, I don't own a good camera. I usually have to borrow one. Thanks for the input you guys

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I think I may know the problem. If you zoomed in close on a dull knife, there'll be a flat surface on the edge where it should be a corner. A big mistake a lot of people make is not sharpening to the point where both sides meet in a corner, instead they get very close but not quite there. Murray Carter's technique is to use the three finger test; put the thumb on the spine of the blade and gently move three fingers along the edge (not across, but with). If it slides easily without grabbing or cutting it, you need to grind further. If it grabs your finger (do it gently and you can tell without getting sliced) you know you're there, and can move to finer stones.

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I'm going to take a step back and ask a few questions. Are these knives you've made that you're having trouble sharpening? If so do you have problems sharpening a bought blade?

 

Also, how are you testing sharpness? You may have a good edge that is simple too thick right behind the edge which prevents it from cutting well.

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I would say I have a hard time sharpening any knife. I think its a matter of technique and practice. I usually test sharpness but cutting, or try to cut a piece of paper.

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There are a lot of guys who use the lansky system because they aren't very good with the hand stones... No shame in that. I personally use hand stones, but I would just as happily use a lansky system.

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Some discussion of sharpening philosophy might be in order...

 

The key to getting a sharp edge is to have the two planes of the edge (the secondary bevel) meeting at a point of infinity (the cutting edge).... The two planes do not need to be flat (they can be curved for a convex edge), they just need to meet together at an acute angle. The problem that occurs when sharpening steel is that, when the two planes meet, they will form what is called a burr, which is similar to a piece of foil... extremely sharp but extremely fragile (I've heard this referred to as a wire edge). Therefore, the first order of business is to rub the edge along an abrasive substance until the edge bevels meet and a burr is formed. All steps after the burr is formed are to polish the bevels, refine, and then remove the burr entirely. Usually we will start with a coarse stone to establish the burr, then finer stones to polish. Until the burr is formed there is no use in switching to a finer stone.

 

There are 2 ways I know of to remove the burr once the bevels are polished. One is a method called stropping, where a substance with some 'give' to it (usually leather) is loaded with a polishing compound, and the edge is dragged along this surface until the burr is polished away without completely rounding the edge in the process. The other method is to break the burr loose by flexing it back and forth with very light pressure instead of polishing it away. I find it difficult to describe how this is done, but this is the type of edge I prefer... maybe we should stick with stropping for now.

 

A few words concerning the angle of the secondary bevel.... a perfectly formed 90 degree angle can cut, but this is far from ideal. The finer the angle, the less force is required to cut, and the more fragile the edge becomes. The two extremes would be a Scandinavian style blade and an ax. With a traditionally made Scandinavian style blade, there is no primary or secondary bevel, there is just a single bevel, usually meeting at an angle around 12-13 degrees per side (24-26 degrees inclusive). This makes for a frighteningly sharp, but somewhat fragile edge. On the other extreme is the ax, sharpened to a 25-30 degree angle (50-60 degrees inclusive). This makes for a strong, robust edge that can handle quite a bit of abuse, but requires more force to cut deeply. Somewhere in the middle is where most knives will fall, between say 15 and 22 degrees, depending upon the hardness, type of steel, and required use.

Edited by GEzell

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Thank you GE, that was a lot of helpful info, I just hope I can translate that into results. I guess I just need to work on developing this aspect of bladesmithing, along with all the other aspects.

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Think those guys covered it ha, a leather belt with compound is ideal if you are stropping, I've used the back of a belt I'm wearing, the edge of a sheath.. whatever I can improvisee really. A quick way of removing a bevel if that is the problem is by lightly sticking the knife edge into a scrap piece of wood and dragging it out a few times. Not as good as a strop but somewhat effective.. some people run the blade backwards on a fine whet stone for a few passes each side at a slightly higher angle than the one you used to establish the secondary bevel

Edited by Kenon Rain.

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When I was sharpening a lot of bigger blades I would use the slack part of my belt grinder, starting with 600 grit, bringing it to am edge with 1000grit, polishing it with a 3000grit, then "stropping" it with a felt belt with a little compound.. took all of about 10 minutes from dull to shaving, it's easy to over heat with the fine grits is the only thing. But nice slightly convexed edge in the end if you do it correctly

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I used to practice knife sharpening a lot, and could put a good edge on just about anything. This was 25 years ago.

 

I got away from it, and find myself struggling some with it now. I have simply lost my feel for maintaining the angle of the blade to the stone, and have had to go back to using angle guides.

 

It is my experience that there is no room for error in the blade angle from stroke to stroke. If you are sharpening at 20 degrees per side, then you have to keep it at 20 degrees. One stroke at 22.5 will undo the work from a lot of strokes that you did at 20.

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GEzell nailed almost all the points I'll try to add some more

 

Maintaining the same angle consistently on both sides is very important. If you have to use a jig or a Lansky to do that then do it. You getting a burr on only one side might be a symptom of this

 

If you hold your blade under strong bright light with the edge up the edge should be invisible. If any light reflects off the edge back to your eye that is a flat spot that needs to be ground down.

A properly formed wire edge or burr should be visible and you should be able to push it from one side to the other with a finger by stroking from the back to the edge of the blade.

And because it is important enough to repeat: if you don't have a nice even burr that you can flip from side to side do not move to the next finer grit. There's no point.

Each level of grit will make a finer burr so if you want you blade really scary sharp work the burr off and form a new one with each grit level. Just understand that this takes more steel off and if you do it too much your blade won't last. I usually do it once the very first time and then just maintain it after

 

Good luck

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just as an aside

 

I Like a lot of us used to do my sharping on the grinder, I did a convex edge and buffed the edge to strop. I was very happy with my edges and the performance of my blades... untill I watched a lecture by Roman Landes at Ashoken a few years ago... Roman blew my mind a bit his ideas on thickness and edge retention among other things I am sitll working through. He has micro graph of edges that show information I never thought about, as it relates to sharpening this is what I can away with, a edge that will scrap/shave hair is under 1 micron, one that will cut free standing hair is under 1/2 micro, so I see that as the goal (the keeness is not for the most part relient on angle) what Roman showed is that sharpening just on a DRY waterstone can anneal the edge for 5 microns on a grinder (even with NO color showing) 10-20microns. this does not happe with a wet water or oil stone, the oil/water carries the heat away quickly enough to not affect the steel, (a true wet grinder will also not affect the edge)

 

so I did a test I sharpened one of my chefs knife they way i had allwas done it and one i resharpened with stones and did some cutting ... the stone cut edge out lasted the other edge better than 2-1. I have learned that sharpen is really about two things angle and finish. keeness vs sharpness sharpness is mostly angle (a total angle of 15deg for a razor 40ish for a axe ) keeness is more about how finely polished the cutting edge is honed to. I found in the past I was never going to a fine enough stone.

MP

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I think I may know the problem. If you zoomed in close on a dull knife, there'll be a flat surface on the edge where it should be a corner. A big mistake a lot of people make is not sharpening to the point where both sides meet in a corner, instead they get very close but not quite there. Murray Carter's technique is to use the three finger test; put the thumb on the spine of the blade and gently move three fingers along the edge (not across, but with). If it slides easily without grabbing or cutting it, you need to grind further. If it grabs your finger (do it gently and you can tell without getting sliced) you know you're there, and can move to finer stones.

Murray Carter also does something that I don't think I've seen anyone else do. He gets rid of the burr every now and then in the higher grits to start the next finer grit with a clean edge. He does this by really gently running the edge through the corner of a piece of soft wood or cardboard. I tried this the other day and it worked really well. Sometimes the sharp bit you can feel with your fingers is the jagged edge of the bur, so gently removing that burr frees up your finger tips to feel the actual edge you have produced. Here's a vid that shows him doing it with a straight razor at 6000 grit

 

Edited by Brad Adams

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I based most of my current techniques on Murray Carter's videos and the one Brad posted is certainly one of his best free videos.

James

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I use my belt grinder with a used 120g belt. I feel the edge every now and then to check for the bur, and once I start seeing the bur I'll bring the knife to my buffer. Using a white/fine rouge, I'll ever so slightly buff ONLY the edge equal amounts on both sides. Usually 3 or 4 passes each side. Shaves nice and fine, and then let the customer figure out if he thinks he can get it sharper.

 

Side note, I shoot for 20 to 25 degree angles for my hunting blades. 30 seems a bit "dull" for my purposes.

 

Hope this helps!

Edited by Austin_Lyles

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I use my belt grinder with a used 120g belt. I feel the edge every now and then to check for the bur, and once I start seeing the bur I'll bring the knife to my buffer. Using a white/fine rouge, I'll ever so slightly buff ONLY the edge equal amounts on both sides. Usually 3 or 4 passes each side. Shaves nice and fine, and then let the customer figure out if he thinks he can get it sharper.

 

Side note, I shoot for 20 to 25 degree angles for my hunting blades. 30 seems a bit "dull" for my purposes.

 

Hope this helps!

:blink: 120 grit then buff? If the belt is used enough to put a servicable edge on the blade, it is worn enough to generate way to much heat for working heat treated steel, especially at the thin edge. Even then, the grit is still the same size and isn't able to get the edge much thinner than the grit itself. You are probobly getting a very thick bur edge and then the buffer is knocking it straight and breaking off some of the more feathery bur but not the main bur. That bur can be quite sharp, but it won't stay sharp for long.

My grinder work ends at a 600 grit Trizact (Gator) belt. Then I move to DMT diamond "stones" or my water stones, depending on the style of blade.

James

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I mainly just gave the method my teacher, Lee Oates taught me. He's well respected for heat treating/knife making here in Texas, heat treating for Texaskifemakers. I've cut through two 2x4's and still shaved hair off my arm with a knife sharpened like that. I like an aggressive edge, and let my customers figure out if they want it differently. :)

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How do you define "aggressive edge"?

That term, to me, means an edge that cuts quickly, deeply and with very little resistance. Almost like it is pulling you through the material rather than you pushing it.

The way you used it I am guessing you mean a knife that will take a beating and still cut?

 

The method you describe is exactly how I sharpen machetes and my less expensive hatchets.

But I wouldn't want to slice veggies or cape out a deer with that kind of edge. As the OP was concerned about getting stuff "really sharp" I addressed it from that perspective.

James

Edited by James Spurgeon

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