Stropping a convex edge?

[Rappy]

I am currently saving serious dough on a Bark river Teddy II
It has a Blade length of 7.5 inches and a convex edge and I'd prefer to take care of that edge with stropping
I'd like it for someone to post a tutorial of sorts on the technique, and a good strop to purchase, I've been looking at the knives plus strop block for instance.

 

[RevDevil]

The sticky'd threads, found at the top of every forum hold important information. In this case, a lot of discussion related to your query:
http://www.bladeforums.com/forums/showthread.php/750008-Stropping-angle-plus-pressure
You can also search for topics on here, or maybe some youtube videos might do the trick.

 

[dalefuller]

Rev has listed some good BF links on stropping. You can also see some BRKT stropping vids on KSF's web site. I started with a strop block from Knives Plus. Went from there to the strops and compound that BRKT recommends, then to balsa wood & diamond spray from HandAmerica. That's the one I actually prefer now. The balsa wood and diamond spray just seem to work well for me. After stropping with that, I finish with few strokes on a bare leather strop.

 

[awestib]

If you don't let it get too dull, a nice piece of flat wood in the size that fits you well (2.5 x 8") that is thick enough so you can hold it in your hand too or use it as a bench strop, spray-glue denim on it (easier to replace when too loaded) and use white compound from BRKT or Ryobi or USA Knifemaker or Mother's Mag polishing paste on it - is all you need. The denim takes the compounds well and has the right structure/gif. Alternatively a well made leather strop (thin and hard) is certainly ok but often more difficult to apply the stick compounds on it if you use the smooth side (not the flesh side). In that case I would likely use one of the Boron Carbide emulsions from Jendeindustries, they are reasonable priced and abrade A2 well. I do like the strops from DLT trading, they have thin leather and use the flesh side which again makes it a bit easier to apply stick compounds.

You have to remember though that although you can maintain your convex edge this way, eventually your apex will become more and more obtuse/convex and you will have to "reset" the apex on a stone which opens another big can of worms (see below). Also, you will loose the bite of the edge pretty quick with just maintenance on a strop. It may shave well and even tree top hair but has no bite left. On a knife like the Teddy you may not need bite though?!

Alternatively you can practice how to maintain a zero convex grind (which yours is) on hard backing - it is basically edge trailing starting near the flats adjusting the angle more obtuse every single stroke until reaching the apex. With the right touch, you can feel and hear when you are there. This way you maintain the whole bevel all along. Cosmetically it may not be as nice as a backing with give though.

 

[Obsessed with Edges]

+1 to the denim strop setup with white rouge or other AlOx-based compounds, as mentioned by Andy above.

Regarding resetting the edge, if or when stropping isn't quite getting it done, just apply the same stropping principles as with the denim strop, but instead use a piece of appropriately-selected wet/dry sandpaper glued to a hard backing (glass, stone, hardwood, or even a smooth & strong piece of basswood works). That's how I restore the apex and the 'bite', if the edge starts losing it on the strop; works like a charm. 320-grit in particular is what I find myself going back to, and just a few follow-up passes on the denim strop gets it back in great shape. BTW, to extend and preserve the bite, you can also use a somewhat coarser stropping compound for maintenance, as you go. I've been liking the Sears #2 (grey AlOx) compound on my denim strop lately; it's just a tiny bit more aggressive than the white rouge I've raved about in past posts (from Ryobi), and leaves a little more bite in the apex, for a while longer.


David

 

[foxhunter2]

I can't picture how to strop a convex edge on a flat strop maybe on a hanging belt
Is it possible to convex the edge on a flat stone ??

 

[Obsessed with Edges]

I can't picture how to strop a convex edge on a flat strop maybe on a hanging belt
Is it possible to convex the edge on a flat stone ??

Yes, it's possible, and actually relatively easy. The natural variation in a smooth freehand stroke is all it takes. If you duplicate the easy, flowing motion ordinarily used on a hanging strop, it'll still introduce some convex on a flat or hard stone. Even easier if your strop (or stone) gives you some length for the stroke; a 12" - 18" backing board for a hard strop gives enough length to allow that natural 'swaying' motion conducive to convexing. As an example, the denim strop I've been using is built on a 21" paint-stirring stick I picked up at Home Depot; the length includes the 'handle' on the stick, but I still have about 17-1/2" of denim stropping surface to work with. The key is to start the stroke with contact higher on the blade, well above the edge, and finish it with a feather-light skimming touch just as the shoulder of the apex is 'grazing' into the strop. That light skimming touch at the end of the stroke is what's important, to keep the apex from pressing into the strop substrate and rounding off.

Convexing on a stone can involve different techniques, one of which might be a back & forth scrubbing motion, with some inverted 'arc' to the strokes (as if done in the bottom of a very shallow bowl). Sounds odd, but the motion sort of emulates that. It's the method that's worked best for me so far, when I've convexed on a stone.


David

 

[foxhunter2]

Thanks for that nice explanation I can see it now it's not easy I'm a belt sharpener
and I use leather belt for stropping.

 

[Obsessed with Edges]

Thanks for that nice explanation I can see it now it's not easy I'm a belt sharpener
and I use leather belt for stropping.

If it helps in understanding, when I use my 21" Home Depot paint-stirrer strop, I use it held vertically or diagonally, while sitting in a chair. I support the lower end on my knee, or resting alongside the inner edge of my knee, with the upper handle-end held in my left hand, near-adjacent to my left ear (picture how a cellist would support a cello while seated). I then start the stropping stroke at the upper end (cutting edge UP), positioning the upper portion of the blade against the denim, then sweeping downward while gradually turning the blade so the contact moves towards the apex, finishing by 'skimming' the very shoulder of the apex off the denim just as the blade moves off and away from the lower end of the strop. Then turn the blade over (cutting edge DOWN), and emulate the same motion in the opposite direction, starting at the low end and sweeping the blade upward to the upper end. OR, I'll sometimes switch hands and maintain the downward-sweeping stroke (cutting edge always UP), but done from my other side. If you think about it, this all sort of emulates how a belt might be used as a hanging strop.

A similar setup and method could also be used with sandpaper on a stick or board, as with the strop (and I often do use sandpaper this way).


David

 

[stitchawl]

For my money, nothing beats a hanging strop for a convex edge. Fast and easy, 'almost' no thought involved. Just keep the strop taut and the small pressure of the knife will be enough to cause the convection. Barbers have been doing just that for a looong time...


Stitchawl

 

[REK Knives]

For my money, nothing beats a hanging strop for a convex edge. Fast and easy, 'almost' no thought involved. Just keep the strop taut and the small pressure of the knife will be enough to cause the convection. Barbers have been doing just that for a looong time...


Stitchawl

That's what i use too, w a little bit of compound on it =)

 

[Rappy]

Just read everyones input, thank you again

I had an old belt laying around so I sanded the smooth side to remove the dye then applied green compound, I'll sand the other side and apply white compound later.

The denim strop is a great idea, if I have denim laying around

I plan on sharpening the convex edge with the mousepad method, that knives ship free illustrates on their page.

 

[FTR-14c]

I have a leather belt that I picked up from Good-Will a while back. I put a little white compound on it and use it for touch ups between sharpening. It is mounted on the right side of my bench and just hangs to the floor. When I use it, I pick it up with my left hand and flip it over the corner of the bench so it is horizontal across the counter top. It is pinned at the right corner, my left hand is raised a few inches and stretching it. This leaves me in a good position to to work on my blades.

I have glued leather to boards and tried the firm backing thing but I produce better results with my method and it feels very natural to me.
One thing I will try for sure is the denim strop on a hard back. Maybe i will have better results with that.

 

[BillL]

Yes, it's possible, and actually relatively easy.
Convexing on a stone can involve different techniques, one of which might be a back & forth scrubbing motion, with some inverted 'arc' to the strokes (as if done in the bottom of a very shallow bowl). Sounds odd, but the motion sort of emulates that. It's the method that's worked best for me so far, when I've convexed on a stone.


David

I can't seem to get my Mora very sharp when I strop on a Translucent Arkansas stone (from Dan) or even on a leather charged with green compound. I can get it sharp but not really sharp compared to using the sharpmaker.

Can you show how the scrubbing motion is like?

Thanks

 

[Obsessed with Edges]

I can't seem to get my Mora very sharp when I strop on a Translucent Arkansas stone (from Dan) or even on a leather charged with green compound. I can get it sharp but not really sharp compared to using the sharpmaker.

Can you show how the scrubbing motion is like?

Thanks

Both of those are likely too fine to do what's probably needed; they're basically for finishing and/or polishing edges that are already pretty refined. If the Mora's edge wasn't already fully apexed and pretty sharp, the Translucent Arkansas and the green strop won't be aggressive enough to improve upon it. The Sharpmaker's 'medium' rods in particular would likely do more, and it sounds as if you've already seen that.

The 'scrubbing motion' is actually very simple in principle. Especially on a wide-bevelled knife like a Mora or other Scandi-grind, it's basically just laying the bevel flush to the stone, with a fingertip or two directly above the area being worked, to stabilize it and feel for flush contact, and 'scrubbing' in a back & forth or circular motion. The idea being to quickly thin the existing bevel until the apex of the edge makes contact and forms a burr, indicating the cutting edge is basically as thin as it'll get.

On a Scandi-grind like the Mora, the wide & flat bevel will tend to stabilize everything and minimize convexing on a hard & flat stone. A dished stone would obviously add more convex, with enough grinding done.


David