help - putting on a convex edge

Geode

Geode

Joined
May 12, 2001
Messages
2,947
Hello,

I have a fixed blade with an 8.5" blade that I would like to convert from the regular edge to a convex edge.

My first choice would be using a belt sander with a slack belt, however I do not have one.

Does anyone have suggestions for being able to use other means to get a convex edge that will not take forever?

Thanks in advance.
 
Have you considered contacting a local knife maker and inquiring what he would charge for doing it for you?
I ask because putting a convex edge is possible by hand if you have a month or two to spare and lots of elbow grease.

Or maybe ask someone at a local machinist shop. That is a bit iffy because they may not be as careful with your knife's temper as a knifemaker would be.

Best of luck with this endeavour!
 
Geode :

My first choice would be using a belt sander with a slack belt, however I do not have one.
Click to expand...

Just buy a belt and use that without the sander. Get the lowest grit you can to start off with. This is what you will use to shape the bevel. Then pick up another that is fairly fine, say 100 AO, this will remove all the heavy scratches and leave a very coarse edge. Polish it further if you want to increase the push cutting ability. Ref :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=208093

You can also just use heavy backed sandpaper which isn't made for belt sanders. You can buy it in large rolls. Just make sure that the kind you are getting is made to cut metal. There are softer grades that are only suitable for wood working. You can usually get a sample no problem, so try it out.

-Cliff
 
My first choice would be to have somebody else does it for you!

If, in case you really want to do it... (I mean "try" it, actually)... by yourself, without a belt grinder... traditionally a Japanese whettman would use a CONVEX whettstone, and ground his blade bit by bit with it. (NB: almost every single one of Sammurai sword is a convex blade.)

Still, an honest advice, let's someone else does it for you, as it is darn difficult!!
 
I just wanted to ask something to clarify the issue. Are you talking about putting on a convex edge only, as in just the cutting edge, or having a full convex bevel, as on one of Ed Fowlers knives?
 
No offense meant here, but you are trying to figure out how to put a convex edge on your knife.
Think about trying to sharpen this knife in the field, once this edge is put on!! :eek:
 
Why/how is a convex edge difficult to sharpen? I am considering getting a flat ground blade with a convex edge put on it. This is supposed to be a screaming sharp combo. I think Jerry Fisk does this with his blades. Any input about this would be appreciated.
Thanks,
Mongo
 
I'm lost as to why a convex grind would be hard to sharpen in the field. Because you follow the entire grind with a abrasive, you require no edge guide. There's no need to maintain a strict sharpening angle like you must do on a conventionally ground knife. As a matter of fact, moving to a convex grind gets you away from the hardest part of sharpening a knife.

I've field sharpened convex grinds with scraps of cardboard, pieces of wet/dry paper, and flat stones; and never had a problem. If you know how to sharpen a convex grind, it's absurdly simple to do.
 
I suggest following Cliff's advice. Get a really low grit belt, say 40 grit, that is designed to cut metal and go at it. I think that is your best bet.

What I have done before to put a convex edge on a blade (this one was 7.5") is to make numerous flat sharpenings with a diamond stone and sort of blend them into one curved edge. It is quite effective, although it does take a couple of hours to do both sides.
 
Buzzbait :

I'm lost as to why a convex grind would be hard to sharpen in the field.
Click to expand...

Because of the common belief that you need a slack belt sander to sharpen them.

-Cliff
 
Think about trying to sharpen this knife in the field, once this edge is put on
Click to expand...
Perhaps Mike had the same impression of the convex profile that I have: lots of "shoulder" hiding the edge. If you used the belt on the doorknob approach to create the edge, I presume you have to use a similarly different technique to touch the edge up in the field. I have a similar concern: where can I find a convex field expedient described? (Had I been able to use a stone for a convex edge, I wouldn't have needed to resort to the belt and doorknob. ;) )

Walker
 
Buzzbait, I was just about to recommend that he get ahold of you for some more info, and you beat me to it!

I know precious little about a convex edge, but if I'm to be a serious knut, it's an issue that I must learn. The guy mentioned it in a field setting, is this a good idea?
 
Okay. For those interested in convex grinds, and how to sharpen them, follow this link. Convex Grinds The web page should provide enough knowledge to get anybody started with a convex ground knife. Hopefully I have all of my facts straight, but I'm sure that Cliff can root out any inaccuracies.

Convex grinds are a piece of cake in the field. You can touch the edge up with as little as a piece of cardboard.
 
Originally posted by Buzzbait
Okay. For those interested in convex grinds, and how to sharpen them, follow this link. Convex Grinds The web page should provide enough knowledge to get anybody started with a convex ground knife. Hopefully I have all of my facts straight, but I'm sure that Cliff can root out any inaccuracies.

Convex grinds are a piece of cake in the field. You can touch the edge up with as little as a piece of cardboard.
Click to expand...
Great link, Buzz...answered all of my questions...:D
 
Buzzbait,

Thanks - now I understand your reference to ease of maintenance.

In your final figure, "Stropping on a Soft Surface," you show the blade flat. Clearly, that will mar the blade's finish. May I assume that was just to illustrate the principle and that you may elevate the spine slightly?

Walker
 
The diagram is correct. The goal is to abrade the entire side of the convex ground knife evenly. If you look at the "Effects of Prolonged Sharpening" diagram, you'll understand why. The knife will keep its keen edge over time this way, instead of getting thick behind the edge bevel, as occurs on a flat grind. Elevating the spine would produce the same performance deterioration that occurs on flat ground knives.

Yes, this does affect the blade finish over time. I have Marbles knives that came with a satin finish. They are now closer to a mirror polish, after repeated touch-ups with 1000 and 2000 grit paper. I like to think of this as an improvement though. If you greatly dull the edge, an Arkansas stone will bring the edge back quickly, but will definitely scar the finish. They key is to touch up the blade before it goes too far south, just like should be done on a normal knife.
 
Buzz,

That makes sense for the "convex primary grind and edge bevel." I should have specified that my question applied to the "flat primary grind with convex edge bevel." It looks as if the former were better and actually easier, though.

One further question, please. Does the knife have to travel perpendicular to the belt? With my stones, I "sweep," which pivots the knife somewhere around the hilt. I visualize it not making any difference with the convex grind, but I thought I'd better check.

Walker
 
Walker – I understand now. You are correct. A flat ground blade with a convex edge bevel doesn’t need to be laid flat. Just start at the actual edge bevel, angling slightly so as not to scratch the flat ground part of the knife. Beware though as the smaller the edge bevel, the harder it is to strop this type of edge. A very small convex edge bevel, like on a Sebenza, can actually be quite tricky.

To tell you the truth, I’m not sure about the knife angle in relation to the belt. Maybe Cliff or somebody else can provide more insight on this. I’ve always stropped the knife in a direction that is perpendicular, but not for any particular reason. I know that many people strop their larger blades at an angle, just because the full blade is too big to completely fit on the strop.
 
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