Help!!! My v grinds are turning out convex!

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d.weglarz13

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Jun 4, 2008
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Hey guys. I have been getting a lot better sharpening freehand on my bench stones lately, but still having some trouble. I have a Course DMT 8", and a Fine DMT 8", and then also a Shapton 1000 grit and 2000 grit, and a Strop Bat from JRE.....just for reference.
I have 2 problems. First, even though i am getting sharper edges with more practice, and i feel that my freehand sharpening is getting better with more confidence, I still end up with a somewhat convex edge on my blades, all the while im actually trying for a v'grind, as the stones are flat. I know Ive heard some say that there will always be some convexing in the grind when you do it free hand, but when i look at pics of guys like Knifenut1013, his edges do NOT look convex at all. Is it my technique? The stones aren't dished in any way yet. The convex is very noticeable too, i don't even need a loupe to see its there.
Second question, after all said and done, when i hit the strop(just weight of blade, and what i think is a little shallower angle), it seems that the strop makes my edges dull again, especially on my knives WITH the convex edge, not the v grind. Any advice or ideas? I try very hard not to round the edges with the strop, but that seems like this is what is happening anyway. And, any tips on stropping the tip of the knife? I think i heard many say to come off the strop when the point is in the middle of the strop, right? thanks again for all the help. I can't wait until im good like some of you guys, but I am starting to lose hope......a little. Thanks again guys. Any ideas or tips will be greatly appreciated.

Dave
 
You are getting convexed bevels because you aren't holding the angle steady enough. I have problems with this, too. My best advice is to continue doing what you're doing, and eventually (not in a week, not in a month, and probably not in a year) you'll get better and better. If you like, you can also get a DMT Aligner clamp and use it once or twice a year to set the bevels straight again.

Also, you noted that you have DMT stones and that they have "not yet hollowed." DMT plates are supposed to never hollow out.

And if your strop is dulling your edge, then you probably have a small burr that you are flopping over during the stropping. Either that or rounding it off.

I hope that helps.
 
What kind of grinding movement are you using?

I've found it's very easy to convex a blade on accident if you use both edge trailing and leading strokes. As you draw back there's a tendency for the spine to rise, and as you push forward to drop back down. This will create a motion that will convex.

I avoid this by using my hips, legs and back to make the movement forward and backward, while keeping my hands immobile. I've gotten bevels that look as flat as the ones I can get off a DMT aligner doing this.
 
Best advice I have is to use some sort of clamp or block to prevent the stone from moving at all. Other bit of advice is to always sharpen your knives standing up, with the stone somewhere around the level of your belt buckle or a little lower. Last bit of advice is to use knives you don't care much about till you get a steadier hand. Freehand sharpening relies heavily on using sight, feel, and sound to get the best possible outcome. I'd also recommend going fairly slow with your passes, and using a fair bit of pressure. After a few you'll build up a bunch of muscle-memory and it will get a lot easier.
 
KennyB makes a good point. Due to my limited ability and experience in free hand sharpening, I do something similar. I was told to use the "fine motor skills "of the hands , wrists and fingers to hold a consistent angle of contact between the blade edge and the stones . Use the "Gross motor skills" of the legs, upper arms and shoulders to maintain a repeatable uniform motion which pushes the blade along the stone surface. In practice it looks like rocking forward and backward with the legs while holding the upper body rigid.
Sharpening, using edge leading only strokes has drastically reduced my unintentional convexing. It also seems that the more acute the angle of attack the less the effect of unwanted convexing. You may wish to read this thread complete with diagrams from Twindog on stropping angles and pressure. It is basic but condenses a lot of useful information. OldDude1

http://www.bladeforums.com/forums/showthread.php?t=750008&highlight=correct+stropping+angle
 
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I agree that you're probably not holding the angle steady enough and just thought I'd say that a leather strop tends to naturally convex any bevels but this can be increased/decreased with the amount of pressure you apply. As it has a cushioning effect basically the more pressure you apply the more it will convex any bevels but I'm sure you already knew that. Secondly in response to this and other questions:

"I think i heard many say to come off the strop when the point is in the middle of the strop, right...?"

I find that it's best not to intellectualize too much but instead just feel what I'm doing. Eventually it will just click and you won't know why or how but you'll be getting perfect bevels from choil to tip.
Best,
Gabriel.
 
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You want to stop with the tip of the knife still on the stone or strop. If you pull the tip off then it tends to round the tip off over time and you won't have that nice sharp and pointy tip.

I also dulled my blades when I used chromium oxide on leather. But I cleaned it off and replaced it with diamond spray and immediately had the sharpest blades I have ever had. I have found that if the knife is at least shaving sharp, that the diamond loaded strop will make the knife quite a bit more sharp. If it won't or will barely shave then you are just wasting your time.
 
Okay guys....first, thanks a lot for the replies. I will check out that link now, too. Oh, and I do only use edge leading strokes. You guys pretty much all hit on one main thing......STAND UP!! So far, I have not done this. It makes a lot of sense though, and I will change this in my technique. Also, like you said, its probably a lot more practice, too. I really appreciate the help, and will try standing while sharpening, and let you guys know how it goes.
Dave
anything else you think of, please throw it in!
 
There is nothing wrong with a little convex and the pics of the edges I post have more convex than you think. Do you have any pics?

As you freehand you will never be able to hold the exact same angle but with proper hold, points of pressure applied, and a good "feel" of the bevel you can get really close. Ease up on your pressure as this will help with your angle control along with many other small factors as you sharpen. The more it feels like the bevel is "floating" on the stone the better. This is more of a factor with the diamonds but can be applied to the use of any stone.

IMO you also need a finer stone before stropping.
 
FlaMtnBkr said:
You want to stop with the tip of the knife still on the stone or strop. If you pull the tip off then it tends to round the tip off over time and you won't have that nice sharp and pointy tip.
Click to expand...

Also, remember to spend the same amount of time on the tip (during the stroke) as all other parts of the edge, or else you'll end up flattening the tip.
 
FlaMtnBkr said:
You want to stop with the tip of the knife still on the stone or strop. If you pull the tip off then it tends to round the tip off over time and you won't have that nice sharp and pointy tip.

I also dulled my blades when I used chromium oxide on leather. But I cleaned it off and replaced it with diamond spray and immediately had the sharpest blades I have ever had. I have found that if the knife is at least shaving sharp, that the diamond loaded strop will make the knife quite a bit more sharp. If it won't or will barely shave then you are just wasting your time.
Click to expand...
I've never heard of diamond spray but it certainly sounds very effective. I use a leather paddle strop(two sides) loaded with two oxide compounds to finish off with or just to maintain when there is no need for realigning the edge and it really brings it up to an a hair popping edge every time. Never had any problems with the gray or green oxides so far...
 
I will try to get some pics up soon, but i gotta borrow a camera for that, no big deal. just give me a little while. To be Really honest with you guys, most of the time i just use my DMT Course, and then the Fine, and it is usually Very sharp. Then most of the time i strop, which seems to set me backwards. So, do i make sure to use the finer ones after that? and even get maybe a finer one than those? I could do that if i must. Oh, and before i go to another stone, i usually knock the burr off by running it on a piece of wood. Is that okay also? Thanks, i will try to get pics.
 
Running the edge down a piece of wood will only help with a floppy burr that you can see and move around with your finger. A normal burr will not come off in this way.

The reason I said you need a finer stone is because when you strop you are using a very fine abrasive, if chromium oxide your talking 50,000 grit! so why would you stop at 2k before you strop? That would be like using a 220 stone then trying to jump straight to a 10k stone in hopes it would remove the scratch and polish the edge. Many like to strop far before they should to correct the burr they are unable to remove by hand sharpening with a stone or simply to make a sharp edge. This may work but is far from correct. Sure you can strop a edge after the fine diamond but if you were to strop after a much finer stone you would then see the true capabilities of the micro abrasive and how sharp it really should be for that size of abrasive.
 
Maybe somebody said this but already buy my breakthrough on this problem, and everybody has this problem at first was this:

Keep the action on one side of the blade on a given grit until you raise a burr. Do not go left right left right left right...etc. What that'll do for you is you get your stroke perfected and some muscle memory kicks in and you attack the stroke with the same motion of the hand and arm.

Then, of course, the trick is when you do flip sides, getting that angle exactly the same as the one on the first side. Once I could get a consistent angle on a give side, I still tended to do the other at a little different angle resulting in a asymetrical edge. That is still a little troublesome for me and sometimes I hit it and sometimes I do not.

Freehanded sharpening skill is one of those very valuable life skills that I think everybody should have. It will not come without practice so just keep it up. You are getting there otherwise you would not notice your convexing so in my mind you are making progress. Freehand knife work on a stone is an execise in patience.
 
knifenut1013 said:
Running the edge down a piece of wood will only help with a floppy burr that you can see and move around with your finger. A normal burr will not come off in this way.

The reason I said you need a finer stone is because when you strop you are using a very fine abrasive, if chromium oxide your talking 50,000 grit! so why would you stop at 2k before you strop? That would be like using a 220 stone then trying to jump straight to a 10k stone in hopes it would remove the scratch and polish the edge. Many like to strop far before they should to correct the burr they are unable to remove by hand sharpening with a stone or simply to make a sharp edge. This may work but is far from correct. Sure you can strop a edge after the fine diamond but if you were to strop after a much finer stone you would then see the true capabilities of the micro abrasive and how sharp it really should be for that size of abrasive.
Click to expand...

Right on.

OTOH you *could* make huge jumps in grit size, but you then must spend a HUGE amount of time polishing away material. Just understand that this practice is a lot like digging with a track hoe then back filling with a teaspoon...it could be done, but seems kind of silly.
 
Different strokes for different folks . I don't strop to polish the edge as I don't really care about that . I strop to make sure I've totally removed the burr . Just taking an edge to 300 grit is fine as long as your not planning to shave with it . I adhear with well known writers that the more coarse edge lasts longer . DM
 
knifenut1013 said:
There is nothing wrong with a little convex and the pics of the edges I post have more convex than you think. Do you have any pics?

As you freehand you will never be able to hold the exact same angle but with proper hold, points of pressure applied, and a good "feel" of the bevel you can get really close. Ease up on your pressure as this will help with your angle control along with many other small factors as you sharpen. The more it feels like the bevel is "floating" on the stone the better. This is more of a factor with the diamonds but can be applied to the use of any stone.

IMO you also need a finer stone before stropping.
Click to expand...

Yeah, one thing about free-handing that I learned while being taught to use handfiles, is that you can really think of the work you're doing with "finer" tools as being "fine" work. In other words, don't worry too much about holding a consistent angle on a coarse stone, just get it pretty even. Then on your fine hone, you have less material to "flatten" out. The more you can hold a consistent angle doing the coarse work the better, but you can still basically focus on some things more during a certain point in the process.

The way I relate it to handfiling is stock removal versus lapping. During stock removal, you don't have to worry about much but keeping it relatively the same angle on the entire surface and in the tolerance, but the closer you get it, the quicker the "lapping" process of getting it extremely flat goes. I've lapped tools with handfiles and sandpaper with nothing more than a surface plate and prussian blue and they were ± .005 in. So doing very precise hand work is every bit possible, you just need to pay extra attention to technique.

As far as the topic of polishing goes... Well, is there no benefit in going from a 220 grit stone to a 10K grit stone? Of course there is, because even though you cannot accomplish the same level of polish, the edge is still refined to be smaller than it originally was. Grit progression is very important for the surface polish of an edge, but there's still a huge difference in how refined an edge can be jumping to higher grits. There will still be spots on it that are not as consistent though, much like there would be large furrows where the larger grit cut deeper than where the higher one polished, but in my experience the leap from a very rough edge to one taken off of a higher grit is significant, even if the polish on it was not as refined as it could have been.

All that being said, I think stropping is a weird term, or "strops" themselves are weird tools. The way I see it, a strop is just an abrasive that is softer than steel. You can avoid large amounts of metal removal, but still have something coarse and hard enough to move metal around on a scale small enough. So when talking about removing burrs, I think they're viable, but of course they're not going to refine an edge like taking it to various high grits of stone, then stropping compound, etc.

I've often come into the idea though that polished is better. As if, anything that coarse can do, polished can do better. I don't know if I necessarily agree with that; I sometimes like my edges to have a bit of "tooth" to them depending on the task. I also don't really seem to have the same experiences people have with defending what is required to "shave" with. I mean, I've shaved with my trapper off of a 1K edge and using a leather belt to strop it with, and in the mean time I've ran into people stating you cannot shave with anything less than a hone on a 10K stone. Maybe I didn't really shave as much as I cut hair off my face? Who knows, as far as I'm concerned when it gets to that point you're just splitting hairs--pun intended.
 
The way I see it, a strop is just an abrasive that is softer than steel.
Click to expand...

This is incorrect, the leather itself is soft but the abrasive being used on the strop or the natural silicates if used bare are much harder than steel.
 
knifenut1013 said:
This is incorrect, the leather itself is soft but the abrasive being used on the strop or the natural silicates if used bare are much harder than steel.
Click to expand...

Well, I was more using that as a description of the way I use it, rather than that actually being the properties involved. I had no idea there were even natural silicates on there, I thought it was just all leather.
 
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