Who convexs?

MD13

MD13

Joined
May 25, 2005
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2,362
So, who here convexs their blades when sharpening? I never have before, but I recently got a BRK&T knife with a convex blade which got me interested in it. I read that in oder to do it correctly (full convex) you'd damage the finish on your blade, but it's also much easier to keep sharp. Then there's also blades that have a standard grind with a convex bevel, and so on. I'm just curious as to who here convexs their blades when sharpening, and why. If not, what angles do you usually use on your bevels? Do convex blades actually last longer than beveled blades over the long haul, and has anyone ever sharpened a knife so many times that the blade is pretty much useless?
Just curious. :)
 
When it's a thin convex grind, you can just sharpen it normally. I guess if you sharpened it many many times, it would become thicker at the edge. I don't know how fat the grind is on the BRK&T though.
 
I convex all my Moras. I like the durability of the convex secondary bevel and I find it easier to sharpen. I use a mouse pad sharpening block with wed/dry sandpaper.

Great all around cutting edge and hold up well under hard use.
 
Here's a link to answer some questions you may have.

http://home.nycap.rr.com/sosak/convex.htm

I convex the edges of some of my knives. Knives used for large amounts of woodworking get a convex edge from me. Also, if a knife needs to have a highly polished edge for some reason, I usually convex it. I also own a number of knives with full convex blades, such as Marbles, Bark River, Blackjack and even a custom Dozier.

Sharpening a convex blade properly will definitely alter the finish of the blade, as you are abrading the entire convex of the blade. What finish you end up with afterward depends on what grit you are using to do the sharpening.

Theortically, a full convex blade will keep its edge geometry longer than a flat ground blade, since the thickness behind the edge does not change over time, if sharpened properly. The reality is not quite a good as the theoretical, since people have the natural tendency to concentrate on the sharpened area of the blade.

Remember that convex edges are usually highly polished. They have definite uses where they excel, but are less efficent in other uses where a toothier edge is required. I love convex edges for woodcraft.
 
There's great info over on the BKR&T forum at knifeforums. I just got my first Barkie, and I'm very convinced. It's wicked sharp, and after some use it only takes a little stropping to bring the edge back.

Whether it ruins the finish on your blade depends on what the finish is. Maintaining the convex edge simply requires polishing with a strop, either with fine sandpaper or some compound. You will end up polishing some of the blade when you do this (probably a fair bit of the blade depending on shape). If you don't already have a somewhat polished blade it will change that, and any coating will also suffer. If the blade is already polished (as the Barkies are), then all you are doing is keeping it looking nice :D

Seems easy to me, although it might be too easy for those of you who like to spend a lot of time re-sharpening. I plan to keep the Barkie convex, convert some other edges to convex, but keep a lot of others at whatever profile they came with.

Cheers, and be careful with your wicked-sharp new knife!
Daniel
 
Most of my edges wind up convexed eventually. Reason why is that they generally cut much more efficiently, hold an edge much longer, and are much stronger and simpler to maintain. I've got quite a few safe queens, but I've also got a handful of knives that I use hard, and frequently. by this point in time, I'm far beyond caring about beauty. Although, that being said, I've never found it difficult to just go over the blade with some 1500 or 2000 grit sandpaper, and then hit it with some Flitz and a polishing wheel to make it look like new again.

I also love Scandinavian edges on knives, but probably not quite as much as a convex edge when it comes down to it. Third favorite is a flat grind, and well....I hate to have become one of those opiniated folks...but...I've gotten to where I avoid hollow ground blades as much as possible.

I've seen a couple of my grandfathers knives with the edges sharpened away to uselessness when I was a kid. I do have a Chicago Cutlery Stockman I've had for seventeen years or so with a mainblade that's coming veeeery close to that point.

If you've never tried a convex grind, I'd suggest giving it a shot. BRK&T makes some great knives for the price.
 
Thanks for the info guys. Right along the lines of what I was looking for. :thumbup: Buzz, I've seen that link before. Great info.

Another Q. If a blade isn't a full convex when made, is it worth the effort to convex it? Since it's not fully convexed to begin with, beside the actual cuting properties of the shape, would you really save that much of the blade over time/with use? (or would that depend on the actual bevel angles?)

(i.e. A flat or hollow grind with a convex edge, vs. a full convex)

edit: RWS pretty much answered my question :)
 
I don't think you'd save any blade over time, by convexing a blade that is not fully convexed.

The only big reasons to do so, that I can think of, are to gain some edge durability, to highly polish the edge, and to make it easier to sharpen a very wear resistant type of steel. I had propblems with sharpening a 440V stainless flat ground blade, and resorted to convexing the edge to make sharpening easier.
 
I eventually convex the edge on most of my EDCs. I'll use the factory edge for a while, but as soon as it dulls it'll hit the mousepad sharpener. I find it far easier to maintain a convex edge than it is trying to keep nice even bevels. Plus I like the way it looks.
 
Thanks Buzz. That's pretty much sums up what I was asking. I didn't know whether it was beneficial to convex an existing blade shape for the purpose of extending the life of the blade. It all would boil down to use and frequency of sharpening, but would be negligable when using a knife with a different blade style the same way. (If that makes sense :D ) Unless of course one were convexing a blade to gain the properties of the convex shape. (what Kamagong said)

-D
 
I put convex grinds and edges on my knives. I even will convex a flat or hollow grind. I recommend my customers to maintain a regular routine of stropping. This will keep the edge fresh if you do it on a regular basis. If you loose the edge, the mousepad and wet dry paper is what I recommend. I put scotchbrite finishes on my blades because of the way full convex blades have to be sharpened. My blades can be cleaned up with scotchbrite pads you buy in the supermarket.
Scott
 
So ease of sharpening seems to be one of the main reasons for doing a convex grind on a knife. I'll be giving it a whirl if/when my BRK&T needs a touch up. I've never been worried about scratching a blade. Knives are tools, and tools get dirty :D I wouldn't buy a knife I didn't intend to use.

(BTW, Scott, love the blade at the top of page 3 in your gallery. :thumbup: )
 
Just my little interjection here...

I wouldn't necessarily say ease of sharpening....to be honest, I've spent a couple of years learning how to make the mousepad technique work to its full potential for me; it's been a real bearcat to learn. But the good news, is that I usually only need to do that once or twice a year, the rest of the time stropping the edge does just fine, also once you get the "feel" of it, it's not so bad.

That's just my experience though...most folks have a quicker learning curve...:o
 
MD13 said:
So ease of sharpening seems to be one of the main reasons for doing a convex grind on a knife. I'll be giving it a whirl if/when my BRK&T needs a touch up. I've never been worried about scratching a blade. Knives are tools, and tools get dirty :D I wouldn't buy a knife I didn't intend to use.

(BTW, Scott, love the blade at the top of page 3 in your gallery. :thumbup: )
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Thanks MD13, that knife is in the hands of a Spec Ops soldier in Afganistan.:thumbup:
Scott
 
Runs W/Scissors- Do you find the mousepad technique to work well with thinner blades as well as a little thicker ones? I've been doing some searching and a few people have mentioned they had problems with a mousepad being a little to soft, causing some problems sharpening. Using a piece of leather underneath some w/d sandpaper was mentioned. Any thoughts? (Obviously the mousepad works quite well seing all the different posts mentioning it's success. Just wondering what your personal opinion was, seeing you have some firsthand experience :) )

Scott, our guys can always use some good steel. Glad to see it went to some good use!
 
In my mind there's a big distinction between a full convex grind and a convexed edge. Full convex blades can be a lot of work to sharpen..... unless you just work the edge, which I think is what a lot of people do.

I put convex edges on some of my knives, usually ones with softer steel where I'm going to need a more obtuse edge. I've seen some people tout convex grinds and edges like there's something magically superior about them but I've never seen it ..... however on a whittler, I feel a convex edge on a thin, flat ground blade like that gives you better control on most woods.

I also finish sharpen convex edges with a couple light strokes on a Sharpmaker or similar. Makes maintenance a lot easier, and much quicker for me to get a razor sharp edge that way. I think Opinel recommends microbeveling its convex blades so I guess I'm not the only heretic who does this. :)

BTW on Bark Rivers.... I've owned several and like them well enough, but I've never seen one with edge geometry even close to what Bark River says is optimum, about 13 degrees per side. After working my BRs down (which means refinishing the entire blade :grumpy: ) to about 10-12 degrees per side, lightly convexing the edge and then putting on a 15-18 degree microbevel, they really cut like crazy.
 
Mousepads work well, although I do like to use a leather backing on thinner blades.
 
MD13 said:
Runs W/Scissors- Do you find the mousepad technique to work well with thinner blades as well as a little thicker ones? I've been doing some searching and a few people have mentioned they had problems with a mousepad being a little to soft, causing some problems sharpening. Using a piece of leather underneath some w/d sandpaper was mentioned. Any thoughts? (Obviously the mousepad works quite well seing all the different posts mentioning it's success. Just wondering what your personal opinion was, seeing you have some firsthand experience :) )QUOTE]

Here's what my experience has been...I started out after reading the webpage that Buzzbait posted. (I think alot of us Forumites have gotten learnt up by that page)

I soon found that putting a good hair popping convex edge on a knife was about 20% didactic and 80% trial, error, and developing finesse.

a mousepad CAN work with any blade, but I've found it to be a bit more tricky, and requiring a much lighter touch. The leather backing has worked excellently for me with thinner blades, as have magazines, cardboard, and my latest, a big rubber automotive sanding block. One of the neatest tricks I've found with my SAK was stealing my wifes emery board..errr...that big blocky filey thing the wife uses on her nails. It worked PERFECT! just the right amount of flexibility, with the perfect grit for touch ups, and even polishing the edge. It was lightweight, and easy to use. Only downside is that they're about $6 each, and can only be used a few times. (less than half a dozen with smaller knives)

The best thing I can suggest is to play around with the general concept, and get some cheap knives you aren't afraid to experiment with. (Opinels, Old Hickory, Moras, etc) There's a whole bin of retired kitchen knives at the local Salvation Army I get for less than a dollar each.

And then when you're ready to REALLY start cheating, pick yerself up a one inch belt sander.:D (Especially if you use many large knives)
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Buzzbait said:
The only big reasons to do so, that I can think of, are to gain some edge durability, to highly polish the edge, and to make it easier to sharpen a very wear resistant type of steel.
Click to expand...

None of this is due to the inflection of the curvature (hollow/flat/convex) but rather its severity (the angles of the grind). If in fact you wanted to make a very wear resistant steel the most efficient to sharpen you would hollow grind the blade so that the edge profile was minimal, rather than maximize it, Alvin has discussed this for about 15 years on rec.knives.

If you take a steel like 440V which was both soft and difficult to grind, it responds well to the mousepad method not because it is convex but because that lowers the pressure because steels of that type tend to deform rather than be easily abraded and thus the edge can be difficult to form clean. If the steel didn't have both of those properties at the same time this would not be an issue.

Most of the properties associated with convex grinds in the above have nothing to do with the fact the grind is convex but rather the nature of the primary/secondary grind and the angles of the grind. You can for example take an Opinel which is a convex grind and hollow it out and adjust the edge profile and for some work it will cut better, be more durable at the edge, and sharpen *much* faster, and retain the edge stability.

This doesn't mean everything should be hollow ground, it depends on what is being cut and how.

-Cliff
 
Yup Cliff is on the right track. The reason I like to convex my knives is it thinns the blade behind the edge and is easy to do compared to a hollow grind with out equipment. I personally have never had the mousepad work for me, I think it may be too soft. My best results have ben with a bench hone, the natural slop of free hand sharpening gives a really nice convex blade grind and/or edge.
 
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