Convex with strop and sandpaper - is there a burr??

[confucius37]

I have tried various sharpening methods, and I am currently working on getting my freehand convexing technique better.

I have been able to get a burr going using traditional v-edge sharpening using a japanese water stone and a DMT aligner to keep the angle. I also have the DMT aligner diamond stones that fit into the guide and can get a burr that way as well. Both of these methods use an edge leading stroke (cutting into the stone)

With the convexing method I place the strip of sandpaper onto the stiff leather (it is not soft) and I use an edge trailing stroke. I can see my angle is correct with a sharpie and I examine the edge with a loupe and see it is a fine edge with no defects. I have never been able to feel a burr with this technique however.

My progression with SiC wet/dry sandpaper:
220 grit: 30 strokes per side (alternating 10 strokes each side)
320 grit: 30 strokes per side (alternating 10 strokes each side)
400 grit: 30 strokes per side (alternating 10 strokes each side)
1000 grit: 30 strokes per side (alternating 10 strokes each side)
2000 grit: 20 strokes per side (alternating 10 strokes each side)

Then I move to loaded strops:
Black Compound: 30 strokes per side (alternating 10 strokes each side)
White Compound:20 strokes per side (alternating 10 strokes each side)
Green Compound: 20 strokes per side (alternating 10 strokes each side)
Bare Leather: 5 strokes per side

Steels I have sharpened using this method:
Becker 1095CV - got this sharp, but need to spend more time on it
Mora 1095 - this was the sharpest, the Scandi grind really helped keep my angle steady
GEC 1095 - the small blade makes it difficult to keep my angle constant
GEC O1 - larger blade, but still hard to keep the angle
Boker 1085 (soft steel)
Buck 420HC

Usually the angle is about 40 degrees inclusive

I am able to get a highly polished edge that can shave arm hair, but it is not quite as sharp as I have been able to achieve with a guided v-edge system (hair whittling).

Do you usually see a burr form when you are convex sharpening?

 

[Obsessed with Edges]

Sandpaper sharpening (edge-trailing) almost always produces a burr, for me anyways. Looking at your list of steels you've done, the 420HC is almost automatic, for forming burrs. The carbon steels will also form them easily, though they're usually not as stubborn to clean up afterwards, unlike the 420HC.

I've found it much easier to use this method (sandpaper) for smoothing/rounding the shoulders of the bevel, and once that's established, using a firmer backing under the paper to work the edge itself. It's a little too easy to round over an edge on soft backing, otherwise. I have used my strop block for most of my convexing. It's an oak block with leather (~1/16" thick) on one side. For the convexed shoulders, I use the sandpaper on the leather side. To a limited extent, I might just barely touch the edge itself on that side. Then, I'll flip the sandpaper to the back side of the block (bare oak), and use that to fine-tune the edge. With the hard backing, I'll often use a combination of edge-trailing and edge-leading strokes on the paper. The edge-leading stroke helps to clean up the burrs formed by edge-trailing, and can often add just a little extra 'bite' as well, to the edge.

And here's a little bit of a 'cheating' trick. My favorite edges, by far, have come from creating a shallow (acute) v-bevel with a guided setup (like the Aligner), and then using the sandpaper/convexing method to smooth & round the shoulders, without altering the edge itself. This means keeping the angle conservatively low on the sandpaper. Just 'sneak up' to the edge, but don't alter it on the sandpaper (at least until you're confident enough to do so). After all, even on a 'true' convex, the edge itself will not be as sharp, if there's even the slightest rounding at the edge. The edge of a truly sharp blade will still be essentially a 'V' in shape. Too much curvature there, and it becomes 'blunt'.

 

[confucius37]

I have tried the cheating trick before use the DMT diamond stones and some Buck S30V to get the initial edge and then used the strop to finish it off.

I think you may be right with the firmer backing idea, I may try to rig up a way to firmly clamp down my sandpaper onto a solid wood backing so I can do both trailing and leading edge strokes.

If I could I would just use the aligner for everything, but it is essentially useless for very small blades that are less than 3/4"-1" wide because you can only achieve edge angles that are something like 50 degrees inclusive.

 

[HeavyHanded]

And here's a little bit of a 'cheating' trick. My favorite edges, by far, have come from creating a shallow (acute) v-bevel with a guided setup (like the Aligner), and then using the sandpaper/convexing method to smooth & round the shoulders, without altering the edge itself. This means keeping the angle conservatively low on the sandpaper. Just 'sneak up' to the edge, but don't alter it on the sandpaper (at least until you're confident enough to do so). After all, even on a 'true' convex, the edge itself will not be as sharp, if there's even the slightest rounding at the edge. The edge of a truly sharp blade will still be essentially a 'V' in shape. Too much curvature there, and it becomes 'blunt'.

This one of the reasons I convex with a stone. Establish the apex and keep working on the shoulders to keep the convex shape overall. I am also somewhat amazed at how much better a V grind performs if one thins the backbevel with every sharpening - not convexing, but keeping the geometry thinned out. Even a relatively small amount of time spent doing this will pay off in performance.

FWIW, the other reason I stopped convexing with sandpaper was the very small but persistent burrs that would form and be nearly impossible to remove without a lot of stropping. Due to the very smooth cutting effect one gets from edge trailing on sandpaper over a conformable surface, the burr doesn't look quite the same as one formed on a stone. The burr (actually it might be better described as a wire edge) shows up as a (very small) unified edge that appears across the top of the grind pattern, but only visible opposite the last side worked on. Depending on the steel it can be extremely difficult to remove. Lightly backdragging the edge along a piece of hardwood at a steep angle will make it stand out more if one is there.



Over half of my sandpaper convexed edges (that I thought were OK) failed to pass this test, while all of the ones I'd sharpened on a stone did fine. There's a relationship between speed and metal elongation - knives sharpened on a powered belt sander did not seem to have the same issue. My edges were quite sharp but fairly short-lived and required lots of routine stropping to keep them scary sharp - a dead give away.

 

[Obsessed with Edges]

I have tried the cheating trick before use the DMT diamond stones and some Buck S30V to get the initial edge and then used the strop to finish it off.

I think you may be right with the firmer backing idea, I may try to rig up a way to firmly clamp down my sandpaper onto a solid wood backing so I can do both trailing and leading edge strokes.

If I could I would just use the aligner for everything, but it is essentially useless for very small blades that are less than 3/4"-1" wide because you can only achieve edge angles that are something like 50 degrees inclusive.

Here's something I did, to get a shallower angle with the Aligner clamp. I used a 'spacer' behind the blade spine, made from a piece of zip-tie, to do the edge on this Vic Mechanic (7/16" wide at mid-blade). The angle setting I used was at the 2nd-lowest position, as shown in the 3rd pic:
The size/thickness of the spacer could be tailored to a particular blade, by using different/thicker materials.

 

[Obsessed with Edges]

This one of the reasons I convex with a stone. Establish the apex and keep working on the shoulders to keep the convex shape overall. I am also somewhat amazed at how much better a V grind performs if one thins the backbevel with every sharpening - not convexing, but keeping the geometry thinned out. Even a relatively small amount of time spent doing this will pay off in performance....

I've tended to do that continual 'thinning' of the geometry also, although with my sandpaper/convexing setup. Aside from stropping, I maintain most of my edges this way, and find myself going 'just a little lower & thinner' on the back bevel, each time I touch up a blade on the sandpaper.

 

[confucius37]

That spacer trick is great!

I'll try and reprofile my old Boker Stockman with the DMT aligner and then thin out the bevel with the stropping setup. I am starting to think I like the strop as a edge maintenance tool rather then an edge shaping tool.

You've given me some good ideas Obsessed with Edges, Thanks!

 

[Obsessed with Edges]

That spacer trick is great!

I'll try and reprofile my old Boker Stockman with the DMT aligner and then thin out the bevel with the stropping setup. I am starting to think I like the strop as a edge maintenance tool rather then an edge shaping tool.

Absolutely! :thumbup:

You've given me some good ideas Obsessed with Edges, Thanks!

You're very welcome. Hope all this helps.

 

[db]

Remember that a angle held useing your convex method will end up being higher than when the same angle is held with a jig on a flat hone. Example and all angles are just a guess to show what I mean, holding at 40 degrees and convexing on sandpaper with soft backing could end up at the edge of being 70 degrees due to the curve. a 40 degree jig held flat edge will be 40 degrees at the very edge as well. There could be two different reasons your not seeing a burr 1 is when you alternate strokes a burr will not really form. 2 you could be useing too much presure and rounding your edge at the very tip. I'd lower the angle alot from your 40 degrees. Once you've reground your convex bevel lighten up alot on the pressure for your finishing strokes. You can get a convex edge just as sharp as a flat edge. It's all in the thinness and finish of the edge and both can get crazy sharp.

 

[confucius37]

I spent about 10 minutes regrinding the edge on the clip blade of my old Boker stockman from Extra Coarse to Fine to Extra Fine DMT diamond stones using the aligner jig and the zip tie spacer. Then I finished it off on the strop to remove the burr and get some more polish.

I could feel the burr forming almost immediately, it was almost too easy with the soft 1085 steel on it. The edge I got shaved hair with ease and I'm betting if I could spend some more time I could get it to whittle hair. My next step is to thin out the bevel with some sandpaper on the strop.

db, I know what you mean about the angle, I think for now I will stick to using the jig to form an initial edge since it was so easy and fast compared to the time spent going through the grits with the sand paper.

 

[SunsetFisherman]

One of the sharpest edges possible, that of a straight razor, gets its bevel and edge set on a flat stone and is then stropped for ultimate performance and to maintain the edge. +1 on mixing techniques to get "scary sharp"

 

[Robs92XJ]

I'd just like to point out that you are not limited to edge-trailing strokes when using sandpaper over leather. I've had no problems going edge first (you want fairly light pressure, obviously), and you can cut off the burr just like you would on a stone. In fact, my technique doesn't really change from a stone to sandpaper strop. I start with back and forth "grinding" strokes, finish with edge leading "sharpening" strokes, until I have removed as much of the burr as possible, before proceeding to the next grit.

I do like the idea of sharpening a v-edge and then working the shoulders down. I may try that on one of my opinels the next time it needs sharpening.

 

[cziv]

I spent about 10 minutes regrinding the edge on the clip blade of my old Boker stockman from Extra Coarse to Fine to Extra Fine DMT diamond stones using the aligner jig and the zip tie spacer. Then I finished it off on the strop to remove the burr and get some more polish.

I could feel the burr forming almost immediately, it was almost too easy with the soft 1085 steel on it. The edge I got shaved hair with ease and I'm betting if I could spend some more time I could get it to whittle hair. My next step is to thin out the bevel with some sandpaper on the strop.

db, I know what you mean about the angle, I think for now I will stick to using the jig to form an initial edge since it was so easy and fast compared to the time spent going through the grits with the sand paper.

I'm not understanding the shim at all. Is there one on each side of the blade? It looks like the blade could be clamped in that position with the need of the zip-tie anyway?

 

[confucius37]

I'm not understanding the shim at all. Is there one on each side of the blade? It looks like the blade could be clamped in that position with the need of the zip-tie anyway?

The clamping mechanism is not that strong, its just to keep the blade positioned. The ziptie is there to keep the blade from moving back while you are moving the stone across the blade.

 

[Obsessed with Edges]

I'm not understanding the shim at all. Is there one on each side of the blade? It looks like the blade could be clamped in that position with the need of the zip-tie anyway?

The 'shim' is a single strip of zip-tie, extending the full width (and then some) of the clamp, so it does brace the blade spine on each side of the clamp. As mentioned, if the shim wasn't there, the blade would tend to slip back into the clamp, until it hits the built-in stop seen on the side of the clamp. The shim keeps the blade from slipping back. This is especially important on blades with slick/polished finishes, or with grinds that make it difficult to get a full-contact grip in the clamp (like a hollow grind, which won't be flush to the clamping faces).

 

[cziv]

The clamping mechanism is not that strong, its just to keep the blade positioned. The ziptie is there to keep the blade from moving back while you are moving the stone across the blade.

The 'shim' is a single strip of zip-tie, extending the full width (and then some) of the clamp, so it does brace the blade spine on each side of the clamp. As mentioned, if the shim wasn't there, the blade would tend to slip back into the clamp, until it hits the built-in stop seen on the side of the clamp. The shim keeps the blade from slipping back. This is especially important on blades with slick/polished finishes, or with grinds that make it difficult to get a full-contact grip in the clamp (like a hollow grind, which won't be flush to the clamping faces).

Thanks guys, now I understand. I usually wrap a paper horse-shoe over the spine from bit of paper or matchbook cover to assist the clamp. My aligner holds anything I can get a grip on, very tightly. They're all thicker than those blade tough. I appreciate the quick replies. :thumbup:

 

[Obsessed with Edges]

Thanks guys, now I understand. I usually wrap a paper horse-shoe over the spine from bit of paper or matchbook cover to assist the clamp. My aligner holds anything I can get a grip on, very tightly. They're all thicker than those blade tough. I appreciate the quick replies. :thumbup:

On 'slippery' blades, I usually do something similar. My favorite 'grippy' material for the blade is a piece of med/fine wet/dry sandpaper, wrapped over the spine (with the grit side to the clamp, for obvious reasons). The gritty side won't budge against the clamp, and the paper backing keeps a pretty impressive non-slip grip on a slick or polished blade. It works especially well when wet, which is great for me, because I often use water with my hones. I've tried duct tape, masking/painter's tape, and even some rubberized tapes. But, they have all slipped at least a little bit, when wet. In fact, water will make the masking/painter's tape come off, after a time.

With this small (narrow) blade, I could probably get away with using the sandpaper grip alone. But, there's always a chance that I'll bump too hard into the blade with the end of a hone, and shove the blade back (I've done it more than once). That's mainly what the shim is for.

 

[cziv]

I'll try it out thanks!

 

[confucius37]

Now that we have a discussion on how to use the DMT for greatest effect, how do you use the aligner for larger (longer) blades?

How do you reposition the aligner to keep a consistent angle?

Do you work a single side of the blade down the full length (repositioning the aligner) and work up a burr for the whole length and then repeat the process for the other side?

Do you work in sections at a time working both sides of the blade and then repositioning?

 

[Obsessed with Edges]

Now that we have a discussion on how to use the DMT for greatest effect, how do you use the aligner for larger (longer) blades?

How do you reposition the aligner to keep a consistent angle?

Do you work a single side of the blade down the full length (repositioning the aligner) and work up a burr for the whole length and then repeat the process for the other side?

Do you work in sections at a time working both sides of the blade and then repositioning?

I generally avoid repositioning the clamp, if possible. For this reason, I'll be very selective about picking a location for the clamp that optimizes a certain span of the edge to my preference. There is an obvious disadvantage to the clamped systems, in that there will be some variability in edge angle and bevel width on really long blades (over 5"-6"). More often than not, it's safe to position the clamp somewhere near the mid-point of the blade's length. If you want a more acute/sharper tip to the blade, the clamp could be positioned further away from the tip (which lowers the angle). Conversely, if you don't wan't an extremely wide bevel near the tip (as would be seen at a very acute angle), position the clamp forward on the blade. Because I don't like to reposition the clamp on a blade, I'll avoid using it on knives with blades longer than maybe 8"-10". In fact, with really big blades like that, the biggest limitation is the reach of the hone & guide rod itself. If the hone & guide rod has to reach more than maybe 4"-5" in either direction, it starts getting kind of awkward. I'd be more inclined to use the clamp with a large bench hone, or sharpen on a sheet of wet/dry sandpaper.

In terms of how I work towards the burr on a blade, I usually just stick to one side, until I have a burr along the full length. At that point, I'll flip it over and work the burr from the other side, until it's been turned the other way. HOWEVER, if there's some obvious asymmetry to the existing edge, which might be made worse by staying too long on one side, then I'll work side-to-side as needed to balance things up, then focus on creating a burr after that.