Stropping convex edges--questions

[Bladenoobie1]

Hi,

The knife of question is a custom scandi bushcrafter I got from a maker here 2 months or so ago. Since then, I've put an asymmetrical grind where I convex one side while keeping the other relatively flat. The purpose is to beef up the edge and to make feathers on a feather stick curl out more easily. In conjunction with a TON of stropping I have created a relatively convexed edge.

The problem I have is stropping it. I look at the very edge closely under a lamp and try to strop accordingly from there--when doing that for some reason I am unable to get good results. On the other end I increase angle, probably a little over the edge angle and then strop. For some reason I am getting a "toothier" sharper edge than when I try to strop at the proper angle. The last thing I've tried is placing the edge in relation to the strop at a shallow angle, under the actual edge angle. To compensate for is shallow angle I use a lot of pressure. This produces good results, but not consistently. In one instance I was able to get the edge hair whittling across the whole bevel, but I find it difficult to repeat such results.

In summary, I am having difficulty finding that "sweet spot" where I am really hitting the apex and making it sharper. It might be worth nothing that the knife has a very subtle small recurve due to the lack of a sharpening choil. Any advice will be appreciated.

Thanks,
BN

 

[Sadden]

Hmmmm...

To me this sounds like you have some microconvexity going on , where the very edge of your edge is slightly steeper than the rest of your convex edge. This can be induced by using pressure when one strops.

This picture is a CPM3V knife I stropped with quite a bit of pressure in order to intentionally induce some microconvexity. After that I applied sharpie and went back to my 8shapton. To the naked eye I removed all the sharpie , but this picture tells the true story. I would have to raise the angle several degrees in order to actually hit the edge of the edge.



All that black stuff is residual sharpie. This could definitely be what you are experiencing , making it difficult to diagnose.

 

[HeavyHanded]

When stropping a convex I prefer to use a real hard backing and if necessary, a Sharpie and a loupe. You have to figure, there's only one single angle where you'll have good contact without crossing the apex (rounding the edge). It is somewhat difficult to find that on a conformable surface when grinding - with sandpaper over leather for example - even more difficult when stropping. It will also help quite a bit in keeping the flat side as flat as possible. You might have to grind a fresh cutting edge and start over...

 

[Obsessed with Edges]

As mentioned, too much pressure and/or a substrate that's too soft/conformable are likely creating most of your problems. In combination, they're almost guaranteed to round off the edge a bit.

A stropping surface that's very firm, like wood, or paper over wood/glass/stone, is much more tolerant of heavier pressure (within reason) and so long as proper angle is maintained. The firmer the substrate, the crisper the edge will be, regardless of whether you're stropping a flat or convex bevel. For example, I've lately been stropping on paper over a piece of plywood, and also started experimenting using an interrupted-surface diamond hone under the paper, and I'm getting better results than anything I've previously used. An added advantage to using a firm/hard stropping substrate is, the compounds will work more aggressively, even on more wear-resistant steels that don't respond to the same compounds on softer substrates.


David

 

[Sadden]

Yeah , my strops are all backed on aluminum or glass. That picture was actually hard to get because the roo strops just do not like to do that , in the end I had to use somewhere around 10+ pds of pressure on an EP sized strop to do that. Considering I normally strop as close to 0pds of pressure as I can humanly get. And I couldn't actually do it with the nanocloth. It just was not physically possible.

I guess a person could do this intentionally to give the edge more durability. Say on a chopper. Or a customers knife that you know gets abused.

 

[HeavyHanded]

As mentioned, too much pressure and/or a substrate that's too soft/conformable are likely creating most of your problems. In combination, they're almost guaranteed to round off the edge a bit.

A stropping surface that's very firm, like wood, or paper over wood/glass/stone, is much more tolerant of heavier pressure (within reason) and so long as proper angle is maintained. The firmer the substrate, the crisper the edge will be, regardless of whether you're stropping a flat or convex bevel. For example, I've lately been stropping on paper over a piece of plywood, and also started experimenting using an interrupted-surface diamond hone under the paper, and I'm getting better results than anything I've previously used. An added advantage to using a firm/hard stropping substrate is, the compounds will work more aggressively, even on more wear-resistant steels that don't respond to the same compounds on softer substrates.


David

David, have noticed the trajectory you're traveling on this subject - you are totally working toward a Washboard state of mind! Right down to noticing that some compounds hit way beyond their weight class when you beef up the backing, and using the word "crisp" to describe the resulting edge...Did I mention I'm making a number of 6" "Backpacker's" boards - also a perfect size for folks that hold the knife and the stone while they work...

Martin

 

[Obsessed with Edges]

David, have noticed the trajectory you're traveling on this subject - you are totally working toward a Washboard state of mind! Right down to noticing that some compounds hit way beyond their weight class when you beef up the backing, and using the word "crisp" to describe the resulting edge...Did I mention I'm making a number of 6" "Backpacker's" boards - also a perfect size for folks that hold the knife and the stone while they work...

Martin

I hear ya... :thumbup:

The paper-over-plywood strop, used with some Ryobi 'White Rouge' compound (2-5 micron, as labelled), has really surprised me in it's versatility with a wide range of steels. I've tried it with 1095 (thin convex), 420HC (Case/Buck; very thin convex), XC90 (Opinel 'carbone; very thin convex), 12C27Mod (Opinel stainless, just like the 'carbone' in grind), 440C (1970s Buck; thicker convex), D2 (Queen; thicker convex), VG-10 (Mcusta; thin, flat damascus laminate w/VG-10 core) and even S30V (Kershaw Leek; nearly-flat thin convex), and have noticed added bite in all. REALLY crisp edges with all of them. I'm anxious to also try some 6/3/1 micron Dia-Paste with the S30V and perhaps the D2 on the same setup; I'd think that may take those steels even further. Haven't tested the paper-over-DuoSharp hone enough yet, to draw real firm conclusions as compared to the plywood backing, though it still seems to work well. I use temporary adhesive on the plywood, to firmly stick the paper, but obviously haven't wanted to do this with the Duo-Sharp hone. Even sticking the paper to the backing makes a difference in aggressiveness of the compounds used.


David

 

[HeavyHanded]

I hear ya... :thumbup:

The paper-over-plywood strop, used with some Ryobi 'White Rouge' compound (2-5 micron, as labelled), has really surprised me in it's versatility with a wide range of steels. I've tried it with 1095 (thin convex), 420HC (Case/Buck; very thin convex), XC90 (Opinel 'carbone; very thin convex), 12C27Mod (Opinel stainless, just like the 'carbone' in grind), 440C (1970s Buck; thicker convex), D2 (Queen; thicker convex), VG-10 (Mcusta; thin, flat damascus laminate w/VG-10 core) and even S30V (Kershaw Leek; nearly-flat thin convex), and have noticed added bite in all. REALLY crisp edges with all of them. I'm anxious to also try some 6/3/1 micron Dia-Paste with the S30V and perhaps the D2 on the same setup; I'd think that may take those steels even further. Haven't tested the paper-over-DuoSharp hone enough yet, to draw real firm conclusions as compared to the plywood backing, though it still seems to work well. I use temporary adhesive on the plywood, to firmly stick the paper, but obviously haven't wanted to do this with the Duo-Sharp hone. Even sticking the paper to the backing makes a difference in aggressiveness of the compounds used.


David

Another material you might try is the reclaimed grit from the fine side of a SiC stone. Just work up some mud with a piece of clean sawblade, old file etc and some mineral oil. Winds up being pretty fine tho nowhere near the finer alumox compounds. The stuff has a totally different feel to it compared to the lapidary grit, lots of bite. The paper will soak up a lot of the oil if too much lands on the sheet. This strop tends to work well for quite a while compared to other paper strops, does a great job, especially on the tougher steels.
I had to jump through hoops to get the lapidary-grade SiC grit to perform the way I wanted. The reclaimed grit from a stone is not as refined but very easy and effective. The more the oil soaks in and the paper "dries out", the more aggressive it behaves.

Martin

 

[Obsessed with Edges]

Another material you might try is the reclaimed grit from the fine side of a SiC stone. Just work up some mud with a piece of clean sawblade, old file etc and some mineral oil. Winds up being pretty fine tho nowhere near the finer alumox compounds. The stuff has a totally different feel to it compared to the lapidary grit, lots of bite. The paper will soak up a lot of the oil if too much lands on the sheet. This strop tends to work well for quite a while compared to other paper strops, does a great job, especially on the tougher steels.
I had to jump through hoops to get the lapidary-grade SiC grit to perform the way I wanted. The reclaimed grit from a stone is not as refined but very easy and effective. The more the oil soaks in and the paper "dries out", the more aggressive it behaves.

Martin

I sort of touched on this a few weeks ago. I'd picked up a tile rubbing stone (assuming AlOx) at Home Depot; I think I'd seen you comment on these here, and was curious about them. I had gently rubbed it against one of the two SiC stones I have (one Norton Economy from HD, the other an Ace Hardware smaller equivalent). Only issue was, the grit that came off I suspect was a mix of the two; hard to tell which one was the greater portion of the mix. Tried stropping on paper with some of the 'dust' mixed in Vaseline, but it was too unpredictable and obviously unrefined; sort of mixed results stropping with it. I'll have to re-generate some grit from just the SiC stone and give that a try.


David

 

[HeavyHanded]

I sort of touched on this a few weeks ago. I'd picked up a tile rubbing stone (assuming AlOx) at Home Depot; I think I'd seen you comment on these here, and was curious about them. I had gently rubbed it against one of the two SiC stones I have (one Norton Economy from HD, the other an Ace Hardware smaller equivalent). Only issue was, the grit that came off I suspect was a mix of the two; hard to tell which one was the greater portion of the mix. Tried stropping on paper with some of the 'dust' mixed in Vaseline, but it was too unpredictable and obviously unrefined; sort of mixed results stropping with it. I'll have to re-generate some grit from just the SiC stone and give that a try.


David

Ouch! the tile rubbing stone is really only good for cleaning cut edges of tile, and lapping other stones, preferably with some loose SiC thrown on top. The older ones looked a lot more like a traditional combination SiC stone and could be sharpened with, but the new ones are no good for that.
The reclaimed grit from a stone whipped up with some hard steel is a different animal. The steel bits are very small, the grit is a bit larger - 20u or maybe a bit larger, but also has many small pieces in the micron range. Main thing is that since it was fractured off the stone, it has a lot of sharp edges yet and bites both on the paper and on the steel. I suspect the screening process for lapidary grit rounds a lot of these edges off, though it still works well for stropping to a crisp high polish if you can pin it down good.

 

[Obsessed with Edges]

Ouch! the tile rubbing stone is really only good for cleaning cut edges of tile, and lapping other stones, preferably with some loose SiC thrown on top. The older ones looked a lot more like a traditional combination SiC stone and could be sharpened with, but the new ones are no good for that.
The reclaimed grit from a stone whipped up with some hard steel is a different animal. The steel bits are very small, the grit is a bit larger - 20u or maybe a bit larger, but also has many small pieces in the micron range. Main thing is that since it was fractured off the stone, it has a lot of sharp edges yet and bites both on the paper and on the steel. I suspect the screening process for lapidary grit rounds a lot of these edges off, though it still works well for stropping to a crisp high polish if you can pin it down good.

That 'Ouch!' reaction is pretty much what I concluded as well (or maybe 'Ugh! or 'Yechh!'). :barf:

That was one of those 'lesson learned' things. In the quest to learn something new, I tried it to see how it would do, and also to reveal the character of the abrasive in the rubbing stone. I found out.


David

 

[Bladenoobie1]

The responses have been really helpful. Thanks guys!

On another note is there any way to grind out the very slight recurve in the blade? Because the knife lacks a sharpening choil I find it really hard to avoid developing a shallow recurve.

EDIT:

I have the means to reprofile the edge relatively quickly but I do not want to deepen the shallow recurve. If anyone can give me advice as to how I can reprofile futher without deepening the recurve I'll probably grind out a new edge and try to keep it more flat.

 

[Fred.Rowe]

Strop just enough to achieve the goal. Its easy to over strop, over grind, over stone; over a lot of things. Making knives for 15 years has taught me to begin the final edge when you begin the knife; it happens in the planning stage; from spine thickness, taper, bevel angle, bevel finish, ultimately to the cutting edge. Bad planning, bad design, results in a bad edge, a poor cutter. Think about the edge when you pick the steel, chances are you are going to build a knife that takes little stropping, little re-grinding, in short its easy to maintain.

Good points guys; I like reading your post, interesting stuff, Fred

 

[HeavyHanded]

The responses have been really helpful. Thanks guys!

On another note is there any way to grind out the very slight recurve in the blade? Because the knife lacks a sharpening choil I find it really hard to avoid developing a shallow recurve.

EDIT:

I have the means to reprofile the edge relatively quickly but I do not want to deepen the shallow recurve. If anyone can give me advice as to how I can reprofile futher without deepening the recurve I'll probably grind out a new edge and try to keep it more flat.

You can do it freehand on a stone, just have to maintain pressure right on top of that area and not let the handle dip - this is real easy to let happen. It might take a bit of time and effort grinding on just that spot to make it happen - probably a good idea to do it over the course of a few sharpenings if its somewhat pronounced. You'll see the grind pattern advance from above and below the recurve portion. Have had to do this on a several knives that came from the factory with an unadvertised recurve, Seems a lot of belt-sharpened knives come with a subtle recurve. I wound up fixing them over time to minimize unnecessary loss of useful life and save me from the extra work - grind a bunch above and below, and then lightly hit the recurve portion to make it sharp. Eventually you'll catch up and it'll be flat. Removing a bunch of metal from the back bevel right above the ricasso/choil region will also help it cut better, as these are often a bit thicker from the factory than they aught to be.

Martin

Edit to add: I usually work the edge at about a 45 degree rake to the grind path, but in this area, especially if I want to work it tight to the ricasso/choil, have no choice but to work it dead perpendicular to the grind path. When stropping I generally revert back to a 45, but at that point most of the stock removal is all done and its mostly surface polish - final edge treatment.

 

[Sadden]

The responses have been really helpful. Thanks guys!

On another note is there any way to grind out the very slight recurve in the blade? Because the knife lacks a sharpening choil I find it really hard to avoid developing a shallow recurve.

EDIT:

I have the means to reprofile the edge relatively quickly but I do not want to deepen the shallow recurve. If anyone can give me advice as to how I can reprofile futher without deepening the recurve I'll probably grind out a new edge and try to keep it more flat.

There are a couple ways to go about this....

http://www.youtube.com/watch?v=Pal9jkQXAsE

 

[Bladenoobie1]

You can do it freehand on a stone, just have to maintain pressure right on top of that area and not let the handle dip - this is real easy to let happen. It might take a bit of time and effort grinding on just that spot to make it happen - probably a good idea to do it over the course of a few sharpenings if its somewhat pronounced. You'll see the grind pattern advance from above and below the recurve portion. Have had to do this on a several knives that came from the factory with an unadvertised recurve, Seems a lot of belt-sharpened knives come with a subtle recurve. I wound up fixing them over time to minimize unnecessary loss of useful life and save me from the extra work - grind a bunch above and below, and then lightly hit the recurve portion to make it sharp. Eventually you'll catch up and it'll be flat. Removing a bunch of metal from the back bevel right above the ricasso/choil region will also help it cut better, as these are often a bit thicker from the factory than they aught to be.

Martin

Edit to add: I usually work the edge at about a 45 degree rake to the grind path, but in this area, especially if I want to work it tight to the ricasso/choil, have no choice but to work it dead perpendicular to the grind path. When stropping I generally revert back to a 45, but at that point most of the stock removal is all done and its mostly surface polish - final edge treatment.

Thanks for the advice! The recurve is not very pronounced and is only noticable if you were to align the edge with something flat. So from what I can understand from what you wrote while I sharpen I should keep most of the pressure on the upper portion of the edge that's higher than the slight recurve? I have a 150 grit nubatama bamboo stone and it cuts fast. I don't want to approach something incorrectly on a fast cutting stone which may result in a permament mistake. Anyhow I can agree on that I do not want to take out any more unnecessary life from the knife unless I have too. I will probably wait until the next time my edge rolls or chips and get everything done in one run.

 

[Bladenoobie1]

There are a couple ways to go about this....

http://www.youtube.com/watch?v=Pal9jkQXAsE

I saw that video before. I cringed.


EDIT:

I just tried stropping the edge over 2 sheets of lined paper with 1 micron boron carbide paste over my shapton glass stone. The results were fairly good and I was left with a refined crisper edge.

 

[HeavyHanded]

Thanks for the advice! The recurve is not very pronounced and is only noticable if you were to align the edge with something flat. So from what I can understand from what you wrote while I sharpen I should keep most of the pressure on the upper portion of the edge that's higher than the slight recurve? I have a 150 grit nubatama bamboo stone and it cuts fast. I don't want to approach something incorrectly on a fast cutting stone which may result in a permament mistake. Anyhow I can agree on that I do not want to take out any more unnecessary life from the knife unless I have too. I will probably wait until the next time my edge rolls or chips and get everything done in one run.

Sad to say you have it right, you have to remove all the steel above and below the recurve till it comes even with the most recessed point. This also means going at it where the steel is probably the thickest to begin with. The good news is that as it evens out, you can blend it into the upper portion/belly and not have to grind it all at the same rate. Don't grind anything that isn't necessary. A Sharpie helps a lot, if only for morale's sake to let you know you are indeed removing metal.

Am pretty sure doing this to a handful of knives is what cemented my operating principle that the fingertip on the guide hand control the show - they can feel if the steel is on good contact with the stone and whether the grip hand is allowing the handle to droop, which will cause further "recurving".


It is also sometimes possible to really concentrate at the base of the blade, right between the recurve and the choil/ricasso - grinding this back more and blending it into the recurve can save some stock removal above the recurve (hope this makes sense) but frequently makes the edge look a little unbalanced/leaf shaped - depends on how it looks to begin with.


Martin

 

[Bladenoobie1]

No your response makes sense. I really appreciated the help. At the moment the edge geometry of the knife is a bit thicker than where I had wanted it, but should still make decent feather sticks--I've not had an opportunity yet to take the knife on a camping trip. Heck I've seen people taking their beckers with a more obtuse geometry and making feathers so I'm not too worried. I'm going to experiment around with different strop surfaces and see the results I get. I have a balsa wood strop and it works great, but it actually is pretty soft on the surface and has a little give, just less than leather.