Convex sharpening...can someone tell me what I'm doing wrong??

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da7703

Joined
Sep 7, 2009
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So I'm trying to do the sandpaper/mousepad method to sharpen my knives to a convex edge. Why? Well, as one forumite likes to put forth (paraphrasing here...) "to put a magical edge that can cut fairy wings with a single pass".

No really, just because it's supposed to be easy, cheap, and portable. So the cheap and portable parts I have down...the easy doesn't seem to be coming.

I've watched the kniveshipfree videos...I read the bark river page....I'm a fairly smart individual, but while I can sharpen the edges they just don't shave hair off my arms. Really, they don't come close...lots of pressure, skin flakes, but the hair remains. I can push cut paper, but again it seems like there's some effort involved that seems to be more than should be needed.

I have a pad, been using mostly 1000 grit (have strop and compound, too, but it seems irrelevant since I can't get the edge I want to polish), and just can't figure out what I'm missing.

I was thinking that the edge is too thick, so I used some 220 to start today, and while it wore some of the coating off the side nicely, I'm not sure that I accomplished much otherwise....it does seem like the edge is thinner, though, but didn't help bring up the sharpness, it would seem.

I'm using little/light pressure, am trailing the edge the way everyone shows, and think I'm generally doing things correctly. This knife did not have a convex edge to start with, but if very clearly does now. Something that I see mentioned in most other methods (stones, tools) is bringing up a burr...I've never seen that mentioned in any of the s.paper/pad methods...why is that? I keep a fairly consistent angle, which I've been trying to make more acute due to thinking the edge may be too thick, but I can hear and feel more work getting done when I raise the angle.

Doing a fingernail/sharpie test, the edge does grab...but at a higher angle than my factory-edged super-sharp flat ground...like maybe 20 degrees higher. Which is why I was trying to make the angle more acute....feel like I'm chasing my tail here.

So, if anyone can give me some tips/hints/suggestions/feedback to help me get on the right track, I'd appreciate it. Thanks.
 
The 1000 wasn't doing much of anything since you hadn't convexed first. You are probably hearing more with a higher angle because you are too high, the edge scraping the paper is going to be noisier than the entire bevel doing it. Whatever angle you are holding the blade at, the final edge angle will be more obtuse. That's what convexing does, a curved transition instead of distinct angle changes from primary to relief to microbevel.
 
hardheart said:
The 1000 wasn't doing much of anything since you hadn't convexed first. You are probably hearing more with a higher angle because you are too high, the edge scraping the paper is going to be noisier than the entire bevel doing it. Whatever angle you are holding the blade at, the final edge angle will be more obtuse. That's what convexing does, a curved transition instead of distinct angle changes from primary to relief to microbevel.
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Thanks for the responses.

So, are you saying that I need to drop the grit lower to get a better convex bevel, and then the edge will be end up getting sharpened after the bevel is dropped? I guess I'm not understanding based on you saying whatever angle I'm holding the blade at produces a more obtuse edge. What angle should I be holding the blade at to achieve a sharper final edge?

I'd like a 20 or less final edge, if you can point me in the proper direction.

I understand and can visualize a convex edge, so I can work with that imagery...

Thanks again.
 
da7703 said:
Thanks for the responses.

So, are you saying that I need to drop the grit lower to get a better convex bevel, and then the edge will be end up getting sharpened after the bevel is dropped? I guess I'm not understanding based on you saying whatever angle I'm holding the blade at produces a more obtuse edge. What angle should I be holding the blade at to achieve a sharper final edge?

I'd like a 20 or less final edge, if you can point me in the proper direction.

I understand and can visualize a convex edge, so I can work with that imagery...

Thanks again.
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Being able to visualize what you are doing is very good as long as you have the right idea ;). When you lay the knife on the paper at the angle you want close you eyes and make a pass. Use your method of visualization and feel, you will be able to feel/visualize what you are doing wrong better. Hope that makes sense.

220grit should get you a coarse shaving edge or at least one that grabs a few hairs.
 
when you sharpen with an edge trailing stroke on a soft backed abrasive, the paper will come up behind the edge as you draw it, like a little wave following a boat. The paper conforms in front of and behind the edge, so you can get rounding on both sides - a convex bevel and a rounded edge. You need a low angle and light pressure.

I try to get my edges to shave at as coarse a grit as possible, my latest was 36. I would do as knifenut says and get the edge shaving at at least 220 before going on. You might want a 400 or 600 step before the 1000, too.
 
hardheart said:
when you sharpen with an edge trailing stroke on a soft backed abrasive, the paper will come up behind the edge as you draw it, like a little wave following a boat. The paper conforms in front of and behind the edge, so you can get rounding on both sides - a convex bevel and a rounded edge. You need a low angle and light pressure.

I try to get my edges to shave at as coarse a grit as possible, my latest was 36. I would do as knifenut says and get the edge shaving at at least 220 before going on. You might want a 400 or 600 step before the 1000, too.
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OK...this I can understand. I'm aware of the "wrap around" effect of the soft-backed sharpening method, but based on these statements, it looks like I'll need to drop my grit.

So, I'm going to use my 220 grit and keep a low blade angle (10-15 degrees by sight), and keep going even if it doesn't "sound" like I'm doing much.

Will this bring up a burr...as I said earlier, no one seems to mention burrs when sharpening with this method. Am I to do one side until it burrs, then do the other side..or should I just do alternating strokes and not worry about the burr?

Sorry if it seems like I'm asking the same stuff over and over, but no one has really said, "this is your problem" and "this is what you need to do to fix your problem". All help is appreciated.
 
Sharpening is a lot about feel, when you have the bevel right its a smooth but solid friction feel. The sound hardheart is talking about will also relate to the feel, when you are too high or low with you angle it will feel like you are removing more metal and you are but only at a small point. Usually this small point of removal is at the edge and will cause a really steep angle on one side, if not corrected it ends up causing problems when you get to the finer grits.

If you want your final edge angle to be at 20 then you need to sharpen at 13-15.

Sorry if it seems like I'm asking the same stuff over and over, but no one has really said, "this is your problem" and "this is what you need to do to fix your problem". All help is appreciated.
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Without seeing the knife in person its really hard to give this answer.
 
da7703 said:
I know...that's why I don't want anyone to be ticked at my multiple questions...I'm just trying to learn....
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No one is going to get ticked, we all learned or are still learning at some point too. Can you take pics?
 
Jeff Clark said:
It is a lot of work to establish a low angle convex edge for the first time. In your case I might start with around 120 grit. This thread here covers some ideas for heavy reprofiling: http://www.bladeforums.com/forums/showthread.php?t=683033
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This is probably the root of my issues...I didn't really think I was radically changing the edge shape. When I hold the edge up to the light, I can certainly see a convexing, but perhaps that's only at the microbevel and not the edge/bevel itself??

I just read about someone working like 15 mins. on an Apex to do some reprofiling....I certainly hadn't laid that much time down on the 220 grit. On the 1000, yes, but not the 220. Guess it's my general approach that's been off..thanks for the remarks.
 
Another thing is the softer your backing is the more it will wrap around and give a higher angle or even round off the edge. Don't press down at all on soft backing.
 
Mousepads can really amplify the "wave" effect. I'd suggest moving to a piece of stiff 1/8" thick leather (9-10oz?) for firmer backing, as it's more tolerant of greater pressure on the blade, which is common when first learning to convex sharpen (still try to maintain light pressure, this just gives you a little leeway). Definitely drop to a lower grit (180-220 range has been fine for me) to reprofile the original flat-bevelled edge to a nice convex shape, then move up from there. You also DO want to form a burr or wire on one side before moving to the other, just like other sharpening methods. Once you've used your finest grit, knock off the burr (I like to use a light edge-leading stroke for this, though the rest of the time I use the edge- trailing method), then go to your compound loaded strop. I have been using this method for about 3 or 4 years now with great success, and I couldn't sharpen a blade to save my life before that. Funny thing is I can now get a fair edge on a stone as well after all this convexing practice.:eek::thumbup: Anyhow, it took me the better part of the first year to really get just the basic hang of convexing, and I continue to improve my technique all the time. Be patient and keep at it.
 
Another little trick that has worked very well for me is to ditch the mousepad and replace it with thin, hard leather. :thumbup:

Then use as light a stroke as your hand is capable of holding. :p

Ben
 
After 30 mins working w/220, then some time w/1000 and 2000...finishing up w/a stropping, I am happy to report my arm is now sporting a generous amount of bald patches!

Thanks for the advice...I simply wasn't bringing the bevel down enough.

I noticed that I didn't do that great of a job on the lower blade section, nearest the choil...the belly to the tip is a razor, but the first inch or so still needs some work.

I'm guessing I just need to target that area a bit more, no? I'm a wee bit disappointed, since I took my time and thought I was being even-handed, but am happy with the progress overall.
 
da7703 said:
...I'm guessing I just need to target that area a bit more, no...
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In my experience, just make sure you feel a burr along the entire length of the blade, and any area you don't, work on a little more until you do. Then move to a higher grit, and feel for the burr again. That usually solves any problems I have with a particular section not being sharp enough. If a section of blade is not sharp enough, do it some more, until it is. Sounds simple, but can be frustrating, until you have some practice at it.
 
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