Need info/tips on convexing

W

WTForce

Joined
Jun 12, 2007
Messages
183
I decided to put a convex edge on my rc-5, I used the mousepad and sandpaper method and I probably watched the videos on knivesshipfree a lot and googled stuff on convexing but I still can't get the edge to be sharp. I'm thinking maybe its the sandpaper grit, I stopped at 600 because it was the highest I have right now.
What I would like to know is, should I continue to higher grits or am I just doing something wrong?
 
You should be able to get it at least somewhat sharp even with 600 grit if your technique is right. Getting a good convex edge is not always easy if you're just starting for the first time. The most common mistake people make is using too much pressure, if you press the blade down too much it will round over the edge. Just strop it lightly. The angle you use depends on the blade, but it should be the lowest angle which will still let you hit the edge, in other words you should see bright metal where the sandpaper is removing material at the very edge. If not, you may need to adjust your angle. Hope that helps.
 
Maintaining a convex blade an converting one are two different things. You got your work cut out for you if your sharpening experience is limited.

If done proper, by the time you get to 600 grit the knife should feel very sharp and be able to shave with little effort.
 
I probably am using too much pressure even if I'm not using any at all, the rc-5 is a pretty hefty knife. Ill give even less pressure a go and see how that turns out
 
Try lifting the spine higher until you can feel, and hear the edge working. Feel free to use a fair amount of pressure to get the convex shape going. Raise the spine a tad more and strop with less pressure.
 
Oh it has the convex shape it just isnt as sharp as it should be getting it from the V-shape to the convex shape wasnt the hard part, getting it sharp was the hard part
 
I believe my post still would apply for the most part. A covexed edge can be a bit deceptive on how sharp it really is compared to how other blades feel.
 
Ok I've tried everything you guys have said to do but no go, the best I have gotten it to do was slice index cards and it would just rip regular paper. I mean the edge feels sharp it passed the pen test thing but it just isn't sharp, I swear this looked really easy in those videos
 
Pressure and angle are key to getting a sharp convex edge. It sounds like you need to still work on those two points, what your describing sounds like a rounded edge caused by the wrong angle and pressure.
 
I was using the angle from before I convexed it which was 40 degrees inclusive, should I go lower?
 
A 20 deg per side sharpening angle when convexing would make your finial edge angle around 25 to 30 per side depending on your backing and pressure. try taking the knife much lower, almost to the point that it would grind the whole saber grind of the knife. Personally I would start the convex from the top of the saber grind
 
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