Convex Edges and Fallkniven

[Ravaillac]

Didn't people use a slack leather strop in the past? They can be loaded up with abrasives and produce convex edges.

Sure they did but there's still a world between (even loaded) strop and proper abrasive paper/belt.

 

[Dannyboy Leather]

Post expired.

 

[Gossman Knives]

Under Wayne Goddard, I learned to keep the primary grind highly polished on convex grinds. This is all that I basically do on the belt grinder (or until the edge gets too thick). Most often the sides of the convex are doing the work before the edge even touches the cutting medium, so I do like a decent finish on the sides.

That is one reason why my own personal use knives look so clean and unused. I mainly hand sharpen but occasionally hit them on a scotchbrite belt on the grinder to fine tune the edge.
Scott

 

[Dannyboy Leather]

Post expired.

 

[sawgrass7]

Ummm....Scott?
What is the sweet knife you are using in your sharpening example photos? I like it.
And what is the sharpener, too? Been looking for a good one, most I find are on the short side. Thanks.

 

[Gossman Knives]

I know a lot of folks are under the impression that if they sharpen their polished convex blades with a stone, they will have a blade full of scratches. If they learn to look at the convex edge very closely, observe what is going on as they are sharpening, forget about what they do with a "V"-grind (to some extent) unneccessary scratches won't occur. Even the owner of Bark River Knives (I have read some of his posts lately) advocates sharpening just the very, very edge of their convex blades - not the whole primary grind. I seriously doubt he personally uses mouse pads in this case.

This convex blade, below, has only been sharpened with stones and maintained on a strop. The sides are mirror finished (not necessary) only because the knife has been used so much. Even experienced knife users usually can't tell that this blade has seen a fine stone. "Easy-does-it", does the trick fast and efficiently.

Exactly, boy it's refreshing to know someone that knows exactly what I mean. It does takes some practice to get it down but with the right abrasives, there is no need to "bear down" when sharpening. I prefer to do it as shown in the pics I posted because I can see what I doing as far as proper angle. Once you get used to it, you'll know the "feel".

sawgrass7 that sharpener is an EZ LAP Sportsman diamond rod. The other two that are similar are made by Lansky and Chefs Choice. I also use the DMT two sided (fine, super fine) paddle sharpener. EZ LAP also makes paddle sharpeners. They fold into the handle like a balisong knife. The knife is a PSK knife with bone scales.
Scott

 

[rifon2]

Could someone please explain the procedure for sharpening a convex edge with a stone or flat diamond sharpener?

Thanks,

I actually do it holding the knife in one hand and the sharpener in the other hand. Look at the attached pics. It is difficult to explain in writing. If you can wait about a week and half, I'm doing a demo at my campout/shop tour next weekend that either Tonym or Joezilla will be video taping and will post on the forum.

These are with a rod but the same can be done with a flat sharpener.

Scott

Many thanks for the reply, especially with pictures.
Looking forward to seeing the video.

This thread has developed to contain a lot of really useful information about sharpening convex grinds.

 

[Rick Marchand]

Magnussen uses a belt sander to produce the convex edge and then finishes the edge with stones. His edges are thus far the sharpest I've ever encountered. I seen lots of blades in my days and attended a few shows now. He gets 'em sharp!

You are too generous, Ken.... but thanks just the same!

I'll give you my take on the convex edge...

Any edge can get shaving sharp. A 90Deg edge can be sharpend to pop hairs... but will it cut efficiently?... hell no. It's what comes after the edge that counts. The shoulder and bevels dictate how a knife will perform.

Convex's claim to fame is that it combines less surface friction (next to hollow ground) with the most mass behind the cutting edge, for strength. At any given time, the material you are cutting is only making contact with a small point on the arch of the convex bevel.

My edges are a mix of three geometries... Flat, Convex and V-grind.

-I forge as close to flat as possible leaving about 3/64" for the heat treat.
-Then I grind the edge to a very shallow convex... actually TOO THIN to be retain sharpness in use.
-My final process is puting a micro-bevel on with a stone (up to 8000grt) then do a final strop with wet newspaper.

Sorry for the bad pic.....

Rick

 

[Hawkings]

You are too generous, Ken.... but thanks just the same!

I'll give you my take on the convex edge...

Any edge can get shaving sharp. A 90Deg edge can be sharpend to pop hairs... but will it cut efficiently?... hell no. It's what comes after the edge that counts. The shoulder and bevels dictate how a knife will perform.

Convex's claim to fame is that it combines less surface friction (next to hollow ground) with the most mass behind the cutting edge, for strength. At any given time, the material you are cutting is only making contact with a small point on the arch of the convex bevel.

My edges are a mix of three geometries... Flat, Convex and V-grind.

-I forge as close to flat as possible leaving about 3/64" for the heat treat.
-Then I grind the edge to a very shallow convex... actually TOO THIN to be retain sharpness in use.
-My final process is puting a micro-bevel on with a stone (up to 8000grt) then do a final strop with wet newspaper.

Sorry for the bad pic.....

Rick

Uuhhmm could you explain that one a bit further? I've never heard of that before.
Do you put the Sunday times on a piece of glass, pour water and strop away?

 

[baldtaco-II]

../
I'll give you my take on the convex edge...


Rick

“Any edge can get shaving sharp. A 90Deg edge can be sharpend to pop hairs... but will it cut efficiently?... hell no. It's what comes after the edge that counts. The shoulder and bevels dictate how a knife will perform.”

Excellent. I've been trying to get that point across here for so long – sharpness and cutting performance are not the same thing. Hence the smile when I see all those I shaved my arm in the garden and made fuzzies, this knife is great posts. So what.

“Convex's claim to fame is that it combines less surface friction (next to hollow ground) with the most mass behind the cutting edge, for strength. At any given time, the material you are cutting is only making contact with a small point on the arch of the convex bevel.”

I'll skate with that to a point. But what of when we cut a soft material? As well as friction we also need to take deflection into account. There are instances in which we could anticipate increased friction with the convex as more comes into contact at any one time, the manifestation of which would be the cut material clinging.

Not surprised you seem to be getting good results given your methods. I can relate.

Some interesting musings here if you've not seen them.

 

[Rick Marchand]

Uuhhmm could you explain that one a bit further? I've never heard of that before.
Do you put the Sunday times on a piece of glass, pour water and strop away?

That's pretty much it, Hawkings...

After I'm done stroping on the 8000grt, I remove the burr by sliding the cutting edge across a piece of wood under its own weight. Then, I lay a sheet of newsprint on the stone and lightly strope, again, under its own wieght.

Mind you I don't do this for every knife... it's a labour of love. Normally I sharpen on a worn 220grt 2x72 belt and finish on a loaded leather 1x30. That get's a great working edge on it...... but its not scarey sharp, like the previous method.

...I'll skate with that to a point. But what of when we cut a soft material? As well as friction we also need to take deflection into account. There are instances in which we could anticipate increased friction with the convex as more comes into contact at any one time, the manifestation of which would be the cut material clinging.

I have to agree with that... it makes perfect sense. That's why kitchen knives are flat. Flat ground knives slice paper more efficiently too!


Okay..... pet peeve...
Folks..... when you slice paper to test a knife's edge.... PLEASE USE NEWSPAPER.... you won't believe the difference. Printer paper is rigid comparison so it's more forgiving with snags.



Rick

 

[baldtaco-II]

Innit, that's why I use Rizla [cigarette papers] held twixt finger and thumb at one end. Printer paper is a lump.

 

[okbohn]

I use a leather hone because I am not skilled enough to use a stone. Not that I couldn't learn...I just got very good using this method and don't want to change.

you guys have probably already seen these, but I love these videos

Sharpening Videos

 

[Rick Marchand]

Innit, that's why I use Rizla [cigarette papers] held twixt finger and thumb at one end. Printer paper is a lump.

Ever try packing peanuts.... or rolled newsprint?

 

[baldtaco-II]

Ever try packing peanuts.... or rolled newsprint?

Never the peanuts but rolled newsprint yeah. I don't get into that stuff so much now but I did have a big phase of that type thing. Now it's mostly just a therapy 'cos I can't play a violin.

 

[baldtaco-II]

you guys have probably already seen these, but I love these videos

Sharpening Videos

Pointed a few people to those vids. Probably the most fuss free intro to this convex thing I've seen. Well worth a flag.

 

[sawgrass7]

Scott - thank you very much for your reply. I love that knife.

This is a GREAT thread, guys - I'm getting so much good stuff here. Thank you all.

 

[trailside22]

Really enjoying the thread and learning a lot!

Scott, do you prefer the EZ Lap Sportsman's Rod or the DMT paddle sharpeners? Your method really makes sense to me, and would be an easy touch up if needed in the field. I am sure after putting a good edge on the blade by hand and then stropping it will be super sharp. Makes since to me, especially on larger knives.

 

[Gossman Knives]

Really enjoying the thread and learning a lot!

Scott, do you prefer the EZ Lap Sportsman's Rod or the DMT paddle sharpeners? Your method really makes sense to me, and would be an easy touch up if needed in the field. I am sure after putting a good edge on the blade by hand and then stropping it will be super sharp. Makes since to me, especially on larger knives.

Actually I use both. The rod to bring up the burr and the DMT fine, super fine to finish the job. Then I strop if I want a polished edge. The most important thing is to maintain the edge. Don't let it dull. Depending on how often you use the knife will dictate how often you need to touch it up.
You're right about larger knives, it does make it easier. I also sharpen hatchets and axes this way.
Scott

 

[Phil Brown]

I've been using that exact same Eze-lap diamond rod for about a year now, and it's my absolute favorite field sharpener. Over time, it's gotten more coarse and raises a burr very quickly, so quickly that the rest of the process seems painfully slow. It leaves a perfectly toothy edge for my paper and cardboard knife. They can be found for around $20, and break down into a ~4 inch package. It comes with a belt sheath, but I mostly carry mine in an enlarged firesteel loop.

This has been a very informative thread; also gratifying to see such a respected knifemaker using roughly the same method/tools as me!