Need advice on convex sharpening

[GoldenAugen]

I'm new to this forum, and new to sharpening knives, so i guess i should jump right in.
Im trying to sharpen my benchmade griptilian for the first time, and i figured i'd go with a convex sandpaper method. After looking around the forum and youtube a lot, i gathered that increasing grits of sandpaper over a mouspad is a good way to do it. I went through four grits (80,150,400, and 600), and then ended by stropping it on the backside of my leather belt. As you can see, I wore the finish off a section above the bevel, making me think that my angle was wrong.

What i wanted some help with is the general technique of this kind of sharpening. I alternated the side of the blade for each stroke, pulling the edge of the blade backwards. Is this method best, or is pushing the blade better? Also, from what i've gathered, you must develop a fold in the edge of the blade, or burr, before going up in grit for sandpapers. Is this always true? At what point do you know to change sandpaper? Also, my knife wasn't as sharp as i would like it, though it's a great deal sharpen than how it started. What should I change for next time I sharpen? Should I increase the grit count? Thanks for taking a look at my post, and i would love any advice the community can give me.

Materials i used

Sorry for the bad pictures, all I have is my phone
Thanks for taking a look guys.
Chris

 

[stoffi]

First of all, I would continue sanding up to 1200 grit, before going to the leather. You don't need to work up a burr if you know what you're doing, which probably doesn't help you very much. Be careful of using too soft of a mousepad. If you do, you must use very light pressure, or you'll make the bevel grind too blunt (it will curve too much). I got a lot of tips from people on here and I feel it's better to try to use something a bit harder than a mousepad, but I still haven't found anything that I like.

You should go from the coarser grit to the finer one when you get the edge sharp. Even with 80 grit the knife will bite (not slip off) your nail or Sharpie if you've done a good job. So, I'll keep testing until I'm happy and then I move on to the next grit. Also, when the knife runs smoothly over the sandpaper, you're getting close. Do another test where you run the edge on your nail or Sharpie from heel to tip. If it runs smoothly without any bumpy-scratchy-feel (consistently smooth), then you're doing it right. Knock off the burr by doing a few straight cuts on some wood once in while. If it slips on the Sharpie after that, then it was only sharp because there was a thin, sharp burr. So, knock it off and keep testing until it bites the Sharpie. Then you can go finer.

It's hard to explain, but keep practicing and you'll develop your own feel for what is right and wrong.

 

[richard j]

chris, i sharpen a lot of knives and most of the knives i make have a convex edge or half convex edge on a chisel grind blade. i have a method that works great for convexing a knife and is a lot easier. its too lengthy to type out but if you send me an email with your number i'll give you a call and tell you how to do it. several guys have tried it with good results.

in the meantime get some 3m brand wetordry paper in the following grits. 280-320-400. i never go over 400 since i see no need to take an edge any finer than that. rje196021@gmail.com

 

[Obsessed with Edges]

First off, I'd recommend using a firmer backing for the sandpaper. It's a little too easy to press the blade too hard/deep into the mousepad, which aggravates the issue you've found (sanding too far up on on the blade). For essentially the same reason, it's also very easy to round off the edge, due to the soft backing allowing the sandpaper to roll/fold around the edge. Some firm leather would be my preference, or you can also use a magazine, catalog or other 'stacked paper' backing. The firmness can be adjusted simply by varying the number of sheets of paper under the sandpaper.

Definitely use an edge-trailing motion (pull the blade, spine first, across the paper).

I would recommend working for the burr, during the coarse stage. For someone who's still trying to learn the method, that's the best way to make sure you've completely apexed the edge. Otherwise, the usual tendency is to stop short of that, which means the edge never gets as sharp as it should be. Once you've verified the formation of the burr along the edge's full length (heel to tip), that's the time to move to the next grit. Use the subsequent grits to gently reduce the burr and refine the edge. No need to re-form the burr with subsequent grits, UNLESS you've inadvertently blunted or rounded off the edge in the following stages. If so, go back to coarse and re-establish the burr as before.

As for improving the edge quality generally, the better you do the initial phase (coarse grit), the easier it will be to really make the edge pop in the following stages. It's very hard to 'fix' an edge that wasn't completely apexed in the coarse stages, by trying to compensate with more work in the subsequent finer-grit stages. Conversely, if you've really done a good job at the coarse grit (edge completely apexed, with a verifiable burr along the full length of the edge), then some gentle refinement is all that's needed afterwards. WITH CARE, that can be done with little time & effort, and produce an excellent finished result. How high you go in grit, is a preference thing. I generally like to finish my edges in the 600 to 2000 grit range. So long as care is taken to AVOID ROUNDING THE EDGE, a higher grit finish can produce an excellent, hard-working and durable slicer. The best overall cutters I have are all finished to ~2000 grit or a little more, finishing with polish on a strop (which is ideal for maintaining these edges too). But a good working edge can be had at 400 grit as well.