Convex edge and edge geometry question

R

RMcClellan

Joined
Dec 26, 2007
Messages
50
Hey guys,
My question is how do you guy gets a convex edge, the easiest way would be best, also how do you all insure you have the correct edge geometry? I've been doing a basic sharpening, I guesss you would call it a flat grid at an angle, it has been suficent as I've been getting a razor edge. But now I'm getting into larger blades that a convex edge would be better, probably be good on smalle blades as well, Thanks Guys, Rex
 
I seen on the internet somewhere a guy made a jig out of a block of wood, some thin foam and sandpaper to sharpen convex grinds. The thing is to have the sharpening surface with a little give to is so it conforms to the convex shape.
 
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A number of possibilities. I use a computer mouse pad, wet/dry paper. The paper is wet [400-600 grit] and the blade is pulled across the paper away from the edge. You just have to learn at what angle [fairly shallow] and how much pressure to use [light] .
The www.fallkniven.com forum has other ways.
 
I would suggest asking this in the Maintenance and Tinkering forum. Although they get asked it all too often (I'd also suggest reading around *before* you ask) it's technically a better/the right place to ask.
 
Maybe I'm lazy, but for users I just use the slack belt on my grinder. After getting the blade to a finished state, I put it on a 400 grit slack belt running slow. Edges are sharp and convex.

When hand sanding the edges in, I use a rubber backed block and wet-or-dry paper. I clamp the blade in the sanding jig and do the edge while holding the block. When it is up to the final grit, I take the blade out and give it its last strokes holding the blade and using the block like mete said.
Stacy
 
How much of a radius are we dealing with; when a "convex" edge is put on a blade?
It must be fairly large. Is it measured in feet or tens of feet? If either of these is the case, how much does it actually effect the cutting, as compared to a "flat edge"?

My personal opinion is that the vast majority of a blades ability to cut anything is 99.9 % the cross section of the blade, the thickness of the spine and whether the blade has a distal taper to it; with the hardening process not being taken into account.
The distance across a secondary edge is so small [.050] on knives that a slightly rounded or flat edge has little effect on actual cutting.
I don't really think you can put a "convex" edge on a fully flat ground blade.

Just my thoughts, Fred
 
Thanks for all the replys,
Lucky Bob, I felt like this IS the right forum for this question, as this is "Bladesmith questions and answers", this is not tinkering or maintenance, I am a new maker and did not fully understand how to aquire a convex edge on a knife I am making.

Fred, this is a hollow grind, 1/4 " stock, It's still pretty thick as I stopped the grind well before my center line. Which brings up the question that I thought of tonight, "Where do I stop my grind?" Or how thick should I leave the edge?

Stacy, I really like the way you explained the way you get your edge, the lazy way, not that doing it the lazy way is a bad thing. I'm so slow at making a knife, I need anything that can speed up the process. Mainly because I do so much of the work by hand with sandpaper, once I get the grind done, through all the grits and as many of the deep scratchs out, I tend to stop before I screw up.

Mete, I like the mouse pad idea, I've been using scrap leather for sanding with higher grits, but a mouse pad would be better, I'm still not sure about sanding away from the edge, that's scary as (knowing me) I will probably bugger up my finish. I will still try it.

I'm going to try all the methods discussed here, and if Fred or anyone can get back to me about the right thickness to leave the ege that would be great too, Thanks so much for the help, Rex
 
Fred,
If you could please answer my question, "how thick should I leave the edge?" Anyone, please chime in. I read somewhere that somebody can't remember crap since the brain surgery!! But what I do remember (the important part) is that he had measurments and had it figured out for the thickness he was using, he did 2 lines, basically stop the grind lines, leaving a specific amount in the center. That would be awesome, he used a dial height gauge to to scribe the line. Any help is greatly appreciated,
Thanks,Rex
 
RMcClellan said:
Hey guys,
My question is how do you guy gets a convex edge, the easiest way would be best, also how do you all insure you have the correct edge geometry? I've been doing a basic sharpening, I guesss you would call it a flat grid at an angle, it has been suficent as I've been getting a razor edge. But now I'm getting into larger blades that a convex edge would be better, probably be good on smalle blades as well, Thanks Guys, Rex
Click to expand...

take a look at this knife. its Convex ground to the edge there is no secondary bevel. However its hand ground on Japanese water stones. No machines but on the handle.

the pictures might help you some.

http://www.bladeforums.com/forums/showthread.php?t=685956
 
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