Sharpening and stropping convex blades

[neeman]

Hi

I am asking for advice on how to sharpen convex blades

I know how to sharpen free hand
I have DMT Aligner for my regular blades
And waterstones for my scandi grinds
I strop on a paddle using mainly white compound
I use the black compound once in a while to get rid of burrs

I have a Bark River Mini Canadian that years ago put a v grind on to it
I want to learn how to sharpen and strop convex and this will be the knife to do it on

I am listening

Thanks

 

[Obsessed with Edges]

It could be as simple as 'stropping' the blade on some wet/dry sandpaper on top of your leather strop (or another similar one). What steel is the blade?

The technique of convexing by hand is exactly the same as stropping, but with more aggressive grit. It's easier still, if the existing V-bevel on your blade is fairly acute (30° inclusive or less), because convexing a V-bevelled edge will almost always widen the edge angle a little bit. If your V-bevel is wider, it may be worthwhile to narrow it a little before convexing (you can use your Aligner for this, so you'll start with as pure and symmetrical bevels as possible). If your edge is currently as sharp as you like it to be, you could even focus on convexing only the shoulders of the V-bevel, and minimizing any contact with the edge itself. If you do work the edge a little bit, doing so with higher grit (1000+) will refine the edge with a minimal risk of over-grinding it. Using the sandpaper over a firmer/thinner backing, like thin leather or even wood or glass will also help minimize rounding of the apex.

You don't even have to do it all at once, either, but instead simply incorporate it into your routine maintence of the edge. Just 'stropping' the blade on the sandpaper occasionally will work the convex into the shoulders of the V-bevel. It'll work faster at grits of ~400 or lower, but you can approach it more gradually by using something like 600-1000 grit.


David

 

[neeman]

David

The Mini Canadian is A2
Hand sharpened now at I presume 22 degrees, nicely even both sides

So what you are suggesting is I knock off the shoulders of the v-grind by stropping on 600-1000 grit paper
Then go to black compound?

Can I 'strop' on 220 grit waterstone?
then on to 1000 grit?

What wrist action do I need to have a rounding action to make a convex angle?
How do I know when I am hitting the edge and loosing the edge
Do I not go beyond my natural 22 degree angle that I sharpen a v grind?
If I am using water stones can I push the blade starting at 22 degrees and not pull cut (strop)

And stropping with compound
I strop my scandi grinds flat with white compound
It brings them to very sharp
How do I use black compound on convex
Back to the question, how do I not round off the edge


Lots of questions
Just I do not have an intuative sense of how to convex, given I have been free hand sharpeninng v-grinds for 50 years....lol

Thanks

 

[HeavyHanded]

You'll have to grind off the shoulder on the V bevel you created, using the 220 grit stone if necessary. Applying the convex maybe you can do with the 1k waterstone, use a very very slight rocking motion. I start with the back bevel furthest away, and as I bring it back toward me I'll elevate the spine slightly, lower it as I move forward, hitting the apex closest to me with a back and forth motion - this is very slight. You can make radial Sharpie marks from spine to apex when you start, this will show exactly where you're grinding. You can also just grind away multiple passes and slowly move the spine up and down as you go. This method maybe a little easier but will leave more variations in the final scratch pattern, but allows you to sculpt the curve of your convex with a lot of precision.
You can very gently finish the edge with a leading or trailing stroke, your preference with the waterstones. A bit of black compound on two sheets of paper wrapped around a dry stone should make it conformable enough to even all the overlapping scratch marks and leave you with a nice EDU edge (remember the Sharpie isn't just for grinding, works well stropping if you have any doubts). Repeat with a finer compound if you're shooting for a more refined edge. I have one Bark River, very thin edge, full convex, doesn't take more than a few degrees of shift to hit the entire bevel face ( I also started out converting it to a V bevel and changed it back). As with all convex conversions, even previously convex edges, go with caution and make sure you're not broadening the edge.

 

[Obsessed with Edges]

David

The Mini Canadian is A2
Hand sharpened now at I presume 22 degrees, nicely even both sides

So what you are suggesting is I knock off the shoulders of the v-grind by stropping on 600-1000 grit paper
Then go to black compound?

If you're happy with the edge angle as it is, taking down the shoulders only would be the simplest way to transition into the convex. What grit you use to start that, is up to you. If you find the 600-1000 grit is taking too long (and you might), you can step to a lower grit like ~400/320. As you work, keep testing the edge by cutting paper or whatever; if you see the need to strop it, use whichever compound you think will do the job.

Can I 'strop' on 220 grit waterstone?
then on to 1000 grit?

If you want to try that, feel free to do so. I suggested starting on the sandpaper and strop, simply because the somewhat more forgiving surface will make shaping the convex easier. On stones, if one isn't comfortable with it, the convex may be a little irregular (flat spots, etc.). But, if you think you want to try it on stones, I would suggest testing the technique with a cheaper knife (or at least, one that you're not afraid to damage in the pursuit of learning ).

What wrist action do I need to have a rounding action to make a convex angle?

I wouldn't even worry about a deliberate wrist action/movement. Freehand sharpening of any kind is naturally going to produce some convex. This is also why I'd suggest using the strop/sandpaper method, because the slightly softer surface will introduce more convex with the same-as-always wrist motion/technique. If deliberately trying to 'shape' a convex on a hard stone, there's a greater risk of over-rounding it, and leaving the edge too thick and blunt. Again, if you want to experiment with this, do so with an 'expendable' blade first.

How do I know when I am hitting the edge and loosing the edge
Do I not go beyond my natural 22 degree angle that I sharpen a v grind?

Test how your existing edge is cutting beforehand, and keep checking/comparing cutting performance frequently as you work. If you're inadvertently hitting the edge, you'll definitely see the cutting performance changing. You could also mark the edge with a Sharpie, and avoid scrubbing off the ink too close to the edge.

If I am using water stones can I push the blade starting at 22 degrees and not pull cut (strop)

Again, if you want to try a different method, use a different blade to see how it works for you.

And stropping with compound
I strop my scandi grinds flat with white compound
It brings them to very sharp
How do I use black compound on convex

Your choice of compound shouldn't be impacted by whether the edge is convexed or not. Use whichever compound you think will work best, based on your previous experiences with it.

Lots of questions
Just I do not have an intuative sense of how to convex, given I have been free hand sharpeninng v-grinds for 50 years....lol

Thanks

I suspect you have more of a sense of it than you might think. That's what I finally realized, after I'd been refining my stropping technique for a while. The technique is there. I literally just picked up a piece of sandpaper one day, laid it across my strop block, and did the same 'stropping' I'd always been doing. And just like that, I was convexing my blade. It literally can be that simple, as long as one doesn't overthink it and get intimidated by the process. It's a lot, lot simpler than most people realize, if they haven't tried it before.


David

 

[neeman]

David and HeavyHanded

Excellent instructions

Now I need to go off and get some paper

Thanks