First try at convex edge.

[Shann]

I gave it a try last night. Started with a Case knife, short pretty thick blade. I had sharpened it a while ago to paper cutting sharp, "almost" shaving sharp. The reason I tried that knife was it was pretty small and I thought it might be easier. I had not been unhappy with its cutting performance.

I started with 220 grit on the mouse pad, worked my way up to 1500 grit. Used a little oil on the sandpaper, not much.

I don't think it worked very well, the edge seems quite "smooth" but not sharp. Don't know if I rounded it off too much, or not enough. I don't know if thats enough info to tell me what to do next, but I'm all ears.

 

[Yvsa]

Shann are you getting a burr all along one side of the blade at the edge before starting on the other side?
The burr is ABSOLUTELY necessary in that it tells you that you have reached the edge and you can start on the other side.
When you get a burr all along the other side again then you're getting somewhere.
Answer this and I'll get back too you, K?

 

[Daniel Koster]

Yes, developing an even burr each side is essential. The sharpening at the higher grits only works if your burr is very fine.

The last two steps are to knock the burr off and strop.


Can you tell if there are any nicks? (fingernail test)
Run your nail down the edge....is it smooth? (should be...or at least, not rough)

 

[Nasty]

Agreed...Burr down one side *mandatory* before flipping...then flip to match. Knocking the burr off is done on the edge of the wood workbench, then it is stropped (green then white) to final state.

 

[Shann]

Ah Ha. I was not getting a burr on one edge before changing. I was doing 10 on one side, 10 on the other.

One thing I thought was interesting was after I spent a while (wrongly) convexing the blade and couldn't get it sharp, I redid it on the sharpmaker. It seemed noticeably sharper than before I spent the time with the sandpaper.

 

[Yvsa]

Ah Ha. I was not getting a burr on one edge before changing. I was doing 10 on one side, 10 on the other.

Shann you can do that but it takes a long, long, time to reach the "center" of the edge.
And it only needs to be done if you're a fanatic about keeping the sides even. Using the mousepad and sandpaper to reprofile and/or to sharpen any convex edge will eventually even out the amount of "angle/radius" that appears on each side of the blade.

My advice at this point would be to go with a much coarser sandpaper, about 150 grit, and using the mousepad get a burr all along one side.
When that is accomplished do the same on the other side and then change to a higher grit to start smoothing the edge to where you want it.
Once you get the edge profiled to a convex and to the degree of polish you want it it will be easy to maintain from then on.

If after getting the edge you want and severely dinging it in use the ding can usually be worked out with the chakmak, or gentle tapping with a small hammer on an anvil or other solid piece of hard material.
Then you might have to go back to the 150 grit to refine the edge and then repolish to what you want.

The "angle" you use to profile/sharpen the edge is important so try too keep it the same on each and every stroke.
The "higher" you raise the back of the blade the more obtuse the edge is going to be of course.
Try to keep the angle at somewhere around 15*, not over, and you will have a good convex for heavy chopping.
For better slicing ability lower the angle to about 10 degrees.
Even the more acute convex edge is going to be stronger than any flat gound edge because there is more material right behind the edge itself so it will hold up better for chopping than a comparable flat ground edge would. I generally sharpen mine in between the 10* and 15* angles, the mousepad automatically generates the radius.
Hope this helps.

Just remember that the most important thing in getting a good edge is getting that burr all along one edge before starting on the other side.

 

[Dave Rishar]

Great info in this thread.

I spent an hour today clearing some more brush with the Kobra -- another successful venture. During the post-op cleanup, I took care of some small dings near the tip with the chakma, cleaned up the rest with a file, and decided to give it a quick stropping on #220 sandpaper. I used about six strokes on one side, raised a burr, then did two or three more on the other side to raise another burr. I didn't have any other sandpaper handy or strops made so I just knocked the burr off with the chakma and called it good.

The funny thing is, while I'm not sure that there's a convex edge there, it came out quite sharp.

What grades of sandpaper are recommended for the different steps in taking an edge further?

 

[Nasty]

What grades of sandpaper are recommended for the different steps in taking an edge further?

Depends...whatcha got?

You can use a full range of grits right up to the final stropping with green then white rouges.

FWIW, you'll do 99% of the work with the first 2 grades of paper you use.

BTW, no water or oil is needed with this method...you *are* going to wear out the paper...that's the whole idea. You use a lube on a stone to reduce wear to it and stop it from clogging. Who cares if you wear out a piece of paper?

 

[namaarie]

~stupid question~

Am I correct in thinking that the burr is the little line of metal dust produced by sharpening? Really new at this convexing, so be nice!

 

[Big Bob]

A burr is what I think is also called a wire edge. You can feel a burr with your fingernail by scraping away from the edge on the opposite side of the blade that you were sharpening. Your fingernail will catch on it-it'll feel like the very edge is folded up. Hope this helps some.

Bob

 

[Daniel Koster]

Am I correct in thinking that the burr is the little line of metal dust produced by sharpening?

Yes. the higher grit you go, the more flexible it becomes. Somewhere past 600, run the end to-n-fro against a piece of hardwood - oak, etc. That will knock the burr off and allow you to start polishing - stropping.

 

[Yvsa]

Am I correct in thinking that the burr is the little line of metal dust produced by sharpening?

Not sure what you mean by metal dust.
But there is no dust to the burr. Big Bob stated it best and correctly.
Dan is also correct in cutting into and dragging the edge across a piece of soft wood like pine to remove the burr prior to stroping.
Oops, Dan said hard wood but soft wood always has worked for me although sometimes I have to cut the wood a few times to wipe the burr off.

 

[namaarie]

Thanks! Please sympathize. I come from the generation of "tactical" knives and diamond files!!

 

[ddean]

A clarification;
just in case somebody sometime ever needs it.

'Knock' the burr off
by -slicing- the edge against the wood,
slicing like cutting vegetables (thanks BruiseL);
not by dragging the blade Left & Right.

I don't mean to nit-pick,
but as a once tech writer I try to err on the side of over-clarifying.

Dan did say 'to & fro',
but a lot of people take that genericly as simply opposite directions.
& Yvsa did say across;
but again, one could take that genericly,
or think of turning the blade sideways to go across to & fro.

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[Daniel Koster]

thanks for clarifying, Dean. Yes, that's the right idea.

 

[BruiseLeee]

I'm still confused.

Does that mean use the piece of wood to realign the burr with the edge as you would a steel?

Or does it mean to cut into a piece of wood as in slicing a tomato in order to shear off the burr?

I've been using the first method and then stroping. Finishing by slicing a few pieces of cardboard then more stroping.



That part wasn't in Pen's video.

 

[ddean]

Or does it mean to cut into a piece of wood as in slicing a tomato in order to shear off the burr?

That's it.

But, whatever works, works.

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[ddean]

It occurs to me.............
[& I know sharpness vs intended use has been discussed previously]

if you put on a burr with coarser grit;
When you remove the burr you have coarser micro-serrations
Which would be better for some types of cutting.
Finer & finer grit results in smaller & smaller micro-serrations---
until there are effectively no serration.
Less serration would be better for other types of cutting
& I think chopping.
For chopping you'd also want a thicker bevel for more durability,
along with the smoothest edge for penetration.
Unless competing for slack-rope cutting
where (I'm thinking) you the thinnest smoothest edge practicable. (Dan?)

Hmmmmmm............

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[Thomas Linton]

This thread really adds a lot of practical information to previous threads on convex sharpening.

 

[Daniel Koster]

You've got the idea, Dean. (thinking cap on straight)

if you put on a burr with coarser grit;
When you remove the burr you have coarser micro-serrations.

This is correct. I did this very thing to a knife two weekends ago. The finest grit I had access to was 220. By varying the pressure (from firmer to lighter) I was able to get an edge that was more even, but still had 220 grit "size" scratches/serrations on it. I polished the heck out of that edge and it would cut nicely, and even shave, but scraped a little when it shaved. That's what people mean when they are looking for a "toothy" edge.

Less serration would be better for other types of cutting
& I think chopping. For chopping you'd also want a thicker bevel for more durability, along with the smoothest edge for penetration.

Beefy edge, fully polished works best. However, real-world wood chopping has a lot more to do with edge geometry and torque, than sharpness. I have used the spine of a machette to do 80% as deep of a cut compared to the edge. (note: you won't get the same results using a khukuri....:footinmou)

Unless competing for slack-rope cutting where (I'm thinking) you the thinnest smoothest edge practicable.

Jury is out on this one. The rope tend to booger your blade. My vote is a med. thick edge. Not thin, nor beefy.

Use the thinner edges for paper, cardboard, etc.

Finer & finer grit results in smaller & smaller micro-serrations--- until there are effectively no serration.

This is almost true. I have examined "fully polished" edges under high magnification and there are still "serrations".

That's why I maintain there are two steps to sharpening: Grinding & Polishing.

Grinding sets the edge geometry. Everything else is varying degress of polishing. There is no such thing as a truly polish (flat) edge. Even in razor blades.