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When convex sharpening...
- Thread starter SC_Dave
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You should expect at least some burr. I say it like that, because most of it will come down to the pressure exerted as the edge is apexing. With a relatively soft backing like the mouse pad, the backing cushions things quite a bit; that tends to minimize pressure exerted laterally against the edge, and burrs usually tend to be smaller as compared to using the same pressure on a harder backing. The edge-trailing stroke also tends to reduce pressure; this is one of the things I like about edge-trailing sharpening in general.
To get some perspective about the differences made by the softness or firmness of the backing, try exactly the same method on a very hard backing like glass. With the same pressure from your hands, burrs will show up much quicker, and usually be larger as well. This is just due to the extra aggressiveness added by the hard backing, so the abrasive works much faster. I tend to favor a harder backing anyway, partly for the speed, and also to minimize rounding of the apex; edges finish up much crisper. With practice, your 'touch' will become tuned to the use of the firmer backing, and pressure can be more easily regulated by your hands to minimize the burrs.
David
To get some perspective about the differences made by the softness or firmness of the backing, try exactly the same method on a very hard backing like glass. With the same pressure from your hands, burrs will show up much quicker, and usually be larger as well. This is just due to the extra aggressiveness added by the hard backing, so the abrasive works much faster. I tend to favor a harder backing anyway, partly for the speed, and also to minimize rounding of the apex; edges finish up much crisper. With practice, your 'touch' will become tuned to the use of the firmer backing, and pressure can be more easily regulated by your hands to minimize the burrs.
David
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I'm getting the dings out of the edge on the pad but as you mention I see no burr building to speak of and it's very slow. I'll try a hard backing tonight. I have a piece of 1/4 glass cut to the size of my sand paper sheets so i'll give it a go. Good information, Thanks David!
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David, I'm not getting a decent edge at all. I can't tell if I'm going too far and rolling the edge or not going far enough to fully apex it. Not sure where to go from here....
I don't think you do videos but I know Jason B and HeavyHanded do. I would love to see one on convex sharpening on a mouse pad with sandpaper.
David
I don't think you do videos but I know Jason B and HeavyHanded do. I would love to see one on convex sharpening on a mouse pad with sandpaper.
David
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Are you using the glass backing, or still working with the mouse pad? What are you using to test the edge, in cutting? Also, what grit are you working with, before testing the edge? If it's still the 150, and the edge is being apexed, the edge will be very coarse and that could be impacting what you're seeing. If so, the touch will need to be very light on the last few strokes, to minimize the heavy burrs.
Some phone book paper can 'diagnose' a lot in determining what's going on. If the edge isn't apexed, or if it's excessively rounded over, the edge will slip over the edge of the paper when trying to cut it. If the edge is apexed & a burr is present (even if it's rolled somewhat), it'll usually cut sort of intermittently or sporadically, with the rolled or burred sections snagging in the paper, while the sharper sections should cut the paper easily. If you don't have the phone book, some similar thin paper from a mail-order catalog or a newspaper circular can substitute for it, and will usually behave similarly.
David
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Using the pad still. Test the edge with magazine paper. I finished with the 150 and went to 400. I tested after the 400. I wasn't finished at 400 but I wasn't impressed with what I had.
David
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With the pad, I'd bet the edge isn't fully apexed, or is being rounded off a bit too much (that could be a bigger issue with the 150 grit; it'll round over the edge even quicker). Those are the issues I had, when first trying out the sandpaper method. When first trying it, I was using the paper over my leather strop block; not quite as soft as a mouse pad, but it still came up a bit wanting for a crisper edge. Started noticing improvement when I flipped the strop block over and used the paper over the bare wood (oak), and that's what got me interested in using firmer backing in general.
David
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At this point I can't tell. I have always heard a convex grind is the easiest to sharpen. Well, not for me. I'm still waiting on that ahh-ha moment I had with my DMT plates and sharpening beveled edge. I tried it on just the glass plate but Had no better result. I'm so frustrated right now I just had to put it all away. It cannot be this difficult.
David
David
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I have one where I do a convex on a hard backed sandpaper (Washboard). Mechanically will be the same as sandpaper over a block of wood, steel plate or glass, or a bench stone for that matter.
https://www.youtube.com/watch?v=SalomUAvMHI
You can make Sharpie marks radially from spine to apex and this will give a good idea where you're hitting. Even on a soft backing there will be a burr once you've gotten to a new edge.
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I was about to recommend Martin's video here. His tips about sensing the change when the apex formed is critical.
OTOH, using mousepad or softer backing, if the amount of pressure, steel type & abarasive matches, it might be easy. However, if they don't match, you'll get either not apexing enough (too light) or rounding (too heavy). The sticky on this subforum about stropping will give you clear idea what happens in relation to pressure.
I'd say I still try improving my technique on washboard. Much practice is needed still. Good luck!
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David,
Don't know if you have access to a fairly close-focusing camera, but if you do, it might be worthwhile to post a pic of the edge. If there are issues with rounding of the apex, or the angle too wide, or steel too thick behind the edge, it might be easier to see with a well-lit and fairly close look in a pic. The advice generated would likely be more worthwhile, based on what we see there.
Another possibility would be to put this particular blade down and do some practicing with a thinner blade in simple steel; maybe a simple kitchen knife, like a paring blade. The downside to trying to learn this new method with a heavy/thick fixed blade is, the amount of steel needing removal can really complicate things. A thick blade sharpened on a softish backing will be much more prone to taking a very wide and likely rounded edge, which will still take much time to correct on harder backing. Using a thin blade on the sandpaper will provide much more immediate feedback as to whether you're apexing fully and also if a burr is forming. Seeing how it takes place on the thinner edge will give you some perspective on what to look for with other knives, keeping in mind that a heavier blade will take more effort and time to produce the same result.
David
Don't know if you have access to a fairly close-focusing camera, but if you do, it might be worthwhile to post a pic of the edge. If there are issues with rounding of the apex, or the angle too wide, or steel too thick behind the edge, it might be easier to see with a well-lit and fairly close look in a pic. The advice generated would likely be more worthwhile, based on what we see there.
Another possibility would be to put this particular blade down and do some practicing with a thinner blade in simple steel; maybe a simple kitchen knife, like a paring blade. The downside to trying to learn this new method with a heavy/thick fixed blade is, the amount of steel needing removal can really complicate things. A thick blade sharpened on a softish backing will be much more prone to taking a very wide and likely rounded edge, which will still take much time to correct on harder backing. Using a thin blade on the sandpaper will provide much more immediate feedback as to whether you're apexing fully and also if a burr is forming. Seeing how it takes place on the thinner edge will give you some perspective on what to look for with other knives, keeping in mind that a heavier blade will take more effort and time to produce the same result.
David
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David,
I think I am seeing a burr along a portion of your edge, in that bright reflective 'thread' in the first pic; that's almost a dead ringer for a burr. And in the third pic, it looks as if the edge might not be fully apexed (looking at the portion of the edge seen below the bright 'dot' of light along the edge). Think I see some more of the same (incomplete apex) in the lower 1/4 or so of the 4th pic as well. Depending on how the blade is oriented in each pic, and therefore what side I'm looking at, it's possible you've stopped a bit short of apex on one side, and generated a burr from the other side at the 'old' apex of the original edge. This would leave a bit of 'microbevel' (remnant of the original bevel) along one side, in between the convexed portions of your new edge. That could definitely present as a 'dull' edge, and it's very common; more so with thicker blades, as it takes quite a while to fully apex from both sides.
Your work looks very good and clean; it just looks as if you haven't quite reached a full apex yet, from both sides. I'd first focus on making sure the (apparent) burr on the one side extends the full length of the cutting edge; then work the other side until the entire length of burr 'flips' in the other direction, indicating you've apexed from that side.
David
I think I am seeing a burr along a portion of your edge, in that bright reflective 'thread' in the first pic; that's almost a dead ringer for a burr. And in the third pic, it looks as if the edge might not be fully apexed (looking at the portion of the edge seen below the bright 'dot' of light along the edge). Think I see some more of the same (incomplete apex) in the lower 1/4 or so of the 4th pic as well. Depending on how the blade is oriented in each pic, and therefore what side I'm looking at, it's possible you've stopped a bit short of apex on one side, and generated a burr from the other side at the 'old' apex of the original edge. This would leave a bit of 'microbevel' (remnant of the original bevel) along one side, in between the convexed portions of your new edge. That could definitely present as a 'dull' edge, and it's very common; more so with thicker blades, as it takes quite a while to fully apex from both sides.
Your work looks very good and clean; it just looks as if you haven't quite reached a full apex yet, from both sides. I'd first focus on making sure the (apparent) burr on the one side extends the full length of the cutting edge; then work the other side until the entire length of burr 'flips' in the other direction, indicating you've apexed from that side.
David
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I'll add to the above good advice, when working with a conformable backing like a mousepad, really lay that spine over. You're probably adding as much as 7-10 degrees per side compared to working on a flat surface. Even the sandpaper over glass likely looses a degree or two to the slight compression of the paper formation. Run it low. A big part of your results might very well be an overly broad apex. I cannot tell from the pics, but the second one down appears to have a marked shift - maybe not.
It is the first thing that comes to my mind when people are working on a mousepad or even some leather under wet/dry and they cannot get an edge to perform adequately.
It is the first thing that comes to my mind when people are working on a mousepad or even some leather under wet/dry and they cannot get an edge to perform adequately.
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Thanks for keeping up with me on the thread. Those pics are not good at all. this Veho USB microscope is at best a PITA to use.
HH when you say "really lay that spine over" are you saying to raise the spine more? I feel like I am raising the spine too much but the way the pics look and considering the height and thickness of this blade maybe I,m not raising it enough.
David, you are right, this blade is 3/16 thick. I'm wondering if I should abandon the pad and sandpaper for my DMT plates....
I made this block today to fit 1/2 sheets of wet/dry paper and have a mouse pad cut to the same size. Also here are a few pics after raising the spine a little more on the wood block with no mouse pad. The rubber bands hold the sand paper in place and keep the block from moving around also.
David
HH when you say "really lay that spine over" are you saying to raise the spine more? I feel like I am raising the spine too much but the way the pics look and considering the height and thickness of this blade maybe I,m not raising it enough.
David, you are right, this blade is 3/16 thick. I'm wondering if I should abandon the pad and sandpaper for my DMT plates....
I made this block today to fit 1/2 sheets of wet/dry paper and have a mouse pad cut to the same size. Also here are a few pics after raising the spine a little more on the wood block with no mouse pad. The rubber bands hold the sand paper in place and keep the block from moving around also.
David
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Using hard hones for thinning a 'thick' edge, before convexing, is something I've done frequently. Thinning to a fairly low-angle V-bevel first (aim a few degrees lower than what you're willing to accept at the finish), and following with the sandpaper can make the process much easier. As Martin has mentioned, sandpaper convexing can add a few degrees to the apex angle if not careful. My own habit would be to follow with sandpaper on a hard backing (over glass, or glued to wood), so as to minimize the conformability under the paper, and keep the edge angle low, or at least within reasonable limits.
I'm certain Martin is emphasizing keeping the spine LOW (closer to the paper), in recommending 'laying it over'. With a soft backing like a mouse pad, this is essential to keep the edge angle from getting too wide. With the harder backing of your block, it'll be easier to keep the edge angle under control. Gluing the paper down will also help, in preventing the paper from lifting or curling around the apex. Also makes the abrasive work more aggressively, if the paper doesn't move at all as the blade is drawn over it. Sticking the paper down also minimizes the extra scratches that'll otherwise mar up the sides of the blade, as would occur when the paper rolls or lifts under the blade.
David
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If you have DMT plates, you can use that. Follow Martin's advice in his video or check out additional video by Murray Carter (cartercutlery) on how to convex blade on a stone (same as on DMT, or sandpaper over wood/glass).
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Last night I got out my DMT plates in an attempt to thin the edge as suggested. Using sharpie radial lines as Martin did in his vid helped significantly in letting me know where my work was. I worked one side checking it often, then looked at the edge straight on and could clearly see I had reduced the shoulder on that side. Flipped to the other side and did the same until I had them equal. Honestly at that point I decided to try to move on to sharpening on the plates. I worked slow in short strokes using a slight rocking motion. Worked my way through C to EEF then stropped. To my satisfaction I got it very sharp. I'll try to post some pics and maybe a vid tonight. If you score points for aesthetics I won't do well as the plates left shiny swirly marks on the cheek. I'm not sure if I want to try to remove these or consider it just part of the sharpening process.
David
David