Quick Convex Question

[Dave568]

I've been attempting to put a convex edge on one of my knives using sandpaper on the back of a mousepad. It has worked alright so far, and I can definitely feel that the edge is convex. However, the knife is still incredibly dull. It barely cuts paper, it can pretty much just rip it. I have been using 400 grit sandpaper so far. I was just wondering if the problem with the edge is my technique, or the paper I am using. I don't have access to any finer grit paper until tomorrow, but I was just wondering if I should keep going at it with the 400 until I get a decent edge, or if it's just not possible to get a decently sharp edge with such coarse paper. Thanks for any help.

 

[gud4u]

Give us some more information on the knife, steel and your technique.

Some possible problems, from what you posted:
- You simply have not formed an edge yet (opposite bevels haven't met).
- Too much pressure, causing edge-rounding.
- Too high angle, causing edge-rounding.

As a guess, you probably haven't removed enough metal to create an edge - there's still a dull edge between bevels.

Google 'sharpening faq'.

Hope this helps!

 

[Lindey]

If you have a semi decent edge on it you might want to try stopping it to get a good sharp edge on it. A method I've used with just stuff on hand was to attach some sandpaper tape to an old belt. Put a loop ad one end that i can iether attach to something or my foot to control the tension while holding the loose end in my hand. Pulling it, i then draw the blade away from me with the edge facing the hand holding the strop. You can then repeat the process with finer grit sand paper. Good luck to you, hope you find something that works.

-Lindey

 

[Gossman Knives]

One thing to be careful of is to not sharpen at a steep angle. You'll end up rounding the edge. Try marking the edge with a Sharpie so you can see where you are hitting the edge on the paper. Strop on a leather belt with an abrasive compound also.
Scott

 

[Cliff Stamp]

It barely cuts paper, it can pretty much just rip it. I have been using 400 grit sandpaper so far. I was just wondering if the problem with the edge is my technique, or the paper I am using. I don't have access to any finer grit paper until tomorrow, but I was just wondering if I should keep going at it with the 400 until I get a decent edge, or if it's just not possible to get a decently sharp edge with such coarse paper.

The paper is too fine. The initial shaping stage should only last a couple of minutes at most and this should leave the edge easily able to slice paper. The edges should now cleanly meet and likely have a significant burr. This burr can be removed with the existing paper and the blade can slice as well as push cut paper readily. This can be achieved with abrasives as low as 90 grit silicon carbide.

You can raise the polish to reduce slicing sharpness and edge retention to increase push cutting ability. Once you have established the convex bevel and are just resharpening it in subsequent sessions then you rarely need to go back to a really coarse abrasive unless there is visible damage. However in general if you are spending minutes sharpening then you would have usually been better off with a more coarse abrasive.

One thing to be careful of is to not sharpen at a steep angle.

Edges can get very sharp even at very high angles, the cutting ability won't be very high, but they will readily cut paper as that is just a sharpness issue.

-Cliff