help me before I go insane convex edges

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wicked1

Joined
Sep 1, 2004
Messages
215
I went and bought a mousepad and some various grit paper to strop my Swamp Rat M6 with. I was cutting steel tonight so the edge had rolled a little. I followed BRKT directions. I took a marker and marked the edge and stropped at about 13 degrees starting with 100 grit. When the edge looked straight again I switched to 220. Now I can cut paper but not very well. No shaving hair performance at all. I am just about ready to say screw the convex and just throw it on the sharpmaker or my edge pro and be done with it at a 21 degree V bevel. Will I lose much performance in doing so? I really want to try this convex edge because this thing has chopped all day like a champ. I dont know what I am doing wrong. I have my microscope amd see the burr forming and then I stropped off the burr with my leather strop. I dont want to goto a higher grit till I get it to at least clean cut paper. Ideas please:confused:
 
If your pressing very hard you could be putting on a much thicker edge than you think with your 13 degrees. That would be my first guess, to fix use a harder backing or lighten up on the pressure.
220 is a fairly coarse edge and should cut fairly well. It does sound like your doing it right grinding until you get a burr then removing it. Do you get the burr on both sides? If so move up to the next grit and see if that helps.
 
after I go get breakfast I will try again using lighter pressure. Yeah I get the burr on both sides. I was using my leather strop to take it off after it had formed on both. The knife blade definately passes the thumb test feels sharp but it isnt.
 
I think you're on the right track, just too coarse at this point. Rub your thumb on your Sharpmakers and then on that 220 paper and you'll feel the difference. Get it as nice as you can with the 220 and then move up to a higher grit lke 400.

Use wet-or-dry sandpaper if you can get it, a couple drops of water on there helps keep it from getting gunked up. You may also try a piece of glass instead of a mousepad; I'm reading some articles about how woodworkers use glass and progressively finer sandpaper to get a perfect edge on their tools.

Hope this helps and don't give up! Sounds like you're getting the convex grind established, now you just have to polish it up. In the future you may not even need to go back down to 100 or 220 grit unless the edge gets really dinged up.
 
wicked1 said:
I took a marker and marked the edge and stropped at about 13 degrees starting with 100 grit.
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13 degrees is a little low for cutting metal. Convex edges are no different than v-ground edges in that you need to match the angles to the knife and steel.

When the edge looked straight again I switched to 220. Now I can cut paper but not very well.
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Even if you are planning on moving to a higher grit then you definately want to get the blade to at least slice newsprint well, meaning it cuts with no tears/slip on a draw. If it isn't doing this then the edges don't even meet. It can also be made to shave and push cut newsprint at the more coarse grits with proper burr removal. All this means is to minimize the extent the edge deforms on most steels which is done by a combination of right pressure, short passes, alternating sides and elevated angles.

Generally you don't need to fully optomize the edge at every grit, but make sure every higher grit does make the edge push cut sharper and still retains strong slicing ability and that any burr is getting significantly reduced with each elevated grit. SR101 isn't prone to heavy burr formation, however if the edge is highly stressed, which sounds reasonable given it was rolled from metal cutting, that metal will tend to break off during sharpening as it is highly fatigued.

In general for a knife that does really heavy cutting, the performance pretty much levels once it slices newsprint well. You won't notice it chopping any better if you go from that to actually shaving above the arm. The edge retention will be higher the sharper you get the knife however no one bats a 1000 when you first pick up a bat.

I am just about ready to say screw the convex and just throw it on the sharpmaker or my edge pro and be done with it at a 21 degree V bevel. Will I lose much performance in doing so?
Click to expand...

You won't notice any different in cutting ability unless you do carefuly measurements on very thin and hard materials and the edge will be more resistant to damage. Most sharpening guides for chopping blades will recommend a very light microbevel for exactly this reason.

wicked1 said:
Yeah I get the burr on both sides. I was using my leather strop to take it off after it had formed on both.
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This generally isn't a good idea, it often causes the burr to crack off. Plain leather is mainly just a cleaning agent for knives, especially those which are hard and/or wear resistant.

-Cliff
 
Unlike Cliff I think you will notice a difference in cutting performance from 13 degrees and 21 degrees. 13 degrees should very noticeably be a better cutter. If you notice that it isn't strong enough and it may not be if your cutting metel you can always raise the angle by just a little until you get the edge strong enough for your use. With that said hopefully it's less than 21 degrees. :)
 
knife is now wicked sharp. I put a 20 degree bevel with a 25 degree microbevel on it. Polished it upto 600 grit. Cuts newspaper great now and shaves. I just went out to do some chopping in the yard real quick to test the edge. I came back in and still slicing newspaper. I am going camping sometime this afternoon. Thats why I was trying to get it sharp its going with me.It chops better than before now. Much deeper chops.
 
wicked1 said:
knife is now wicked sharp. I put a 20 degree bevel with a 25 degree microbevel on it. Polished it upto 600 grit. Cuts newspaper great now and shaves. I just went out to do some chopping in the yard real quick to test the edge. I came back in and still slicing newspaper.
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If you are so inclined I would be interested in how much chopping you can do with it before you lose the ability to slice newspaper. Nothing as specific as 574 chops, just a general idea. The hype about the convex grind has far more myth than fact. Most of the convex grinds that people tend to praise heavily are in fact extremely flat and what is being seen is the effect of a relief grind not the curvature itself.

I would suggest that you try freehand sharpening unless you pack an Edge Pro / Sharpmaker everwhere. To start off, just freehand out any damage and just get the blade to slice paper and then finish on the Edge Pro / Sharpmaker. In a short period of time you will find that your rough shaping will no longer be so rough and you don't need to use a jig or clamp system.

There is something fairly comforting when using a large knife in the brush that you can just pop out a small diafold or just pick up a rock and restore the edge if the need arises.

-Cliff
 
Will do that. I am going to note how long the edge holds today. I usually have a sharpmaker or lansky with me but you are right I need to get the freehand down a little better. I use my boots and my carharts to strop with as well.
 
It can be a bit frustration at first, but sharpening is actually far easier, skill wise, than actually using a knife. Most people either overcomplicate it or really are not sure of the goals. Once you know what is going on then it gets really simple. Grind to shape, remove the burr. That is all you have to do.

-Cliff
 
Generally it won't be because you will hold a different angle pushing away from you than pulling toward you. This doesn't matter anyway unless you are trying to maintain some jig-profile which is never a good idea as it is very difficult by hand to try and match an precise bevel ground at almost exactly 20 degrees (or whatever) per side. This is why the first freehand is usually the longest as you naturally shape the bevel to where you are comfortable. As you sharpen more knives you will get more flexible and thus be able to hone at around 10 vs 15 , but you are never going to get to the point where you can exactly hit 13.5 degrees front and back.

-Cliff
 
my problem has always been getting the angle the same on both sides.
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I've been sharpening free-hand for a number of years, and I still produce slightly differing bevel angles. The difference isn't much, but enough that you can see that one bevel is just a bit higher than the other.

Small bevel angle differences of a couple of degrees really don't matter. You'd really have to create radically-mismatched bevels, similar to a zero grind bevel, before you'd notice a cutting/slicing bias.

Pragmatically, what matters is:
- Sharpness of the edge.
- Adequate edge strength for the range intended of cutting tasks.
 
I also haven't had very good luck convexing with a mouse pad. However, putting on a edge free hand on a bench stone produces a convex bevel and that is how I do all my sharpening now. Everyone favors one side or the other just like Gud4u. I like to round off the shoulder blending the blade grind and edge bevel and the small difference from each side isn't noticable then.
 
You may also try a piece of glass instead of a mousepad; I'm reading some articles about how woodworkers use glass and progressively finer sandpaper to get a perfect edge on their tools.
Click to expand...

I started out in my woodworking hobby using this method. It's called the Scary Sharp System. And while I orignally used the thickest piece of glass I could find at a local glass shop, it wasn't that thick and I ended up breaking it. Instead of buying another piece, thanks to reading woodworking forums I ended up buying a granite surface plate. This month Woodcraft has their's on sale for $19.99. these are Grade A inspection plates flat to .0001 of an inch.

For me it's great for flattening handplane soles from flea market finds which are often in poor shape, but I've moved on to other methods to sharpen cutting edge tools like chisels and plane blades. That's because in the long run, it's more cost efficient to use a Japanese waterstone, than it is to keep buying sandpaper. But it is a good initial introduction for those just getting into the hobby for something to use before they decide which sharpening system they want.

Btw, I'm just getting into knives, and I've enjoyed reading through the forums. I might even sell off some of my antique handplanes to pay for this new hobby of mine. :)
 
just got home. My Swamp rat will still shave hair and slice newsprint.I impressed the hell outta my buddy last night. I dropped an 8" diameter hickory tree with my M6. I tried chopping till I felt I was going to die of heat exhaustion then I grabbed a pipe wrench out of my truck and pounded the living hell out of that swamp rat till I couldnt go any farther in and pulled it out and repeated. Took about 15 to 20 minutes to get it to go down but it went. And my Rat took no damage whatsoever. The pipe wrench sustained some though! After It fell I used my Ka-Bar to slice and chop the littler branches off and the swamp rat to cut it into firewood. Kept me busy most of the evening. I chopped for quite a while. Took some beer cans and cut them open and placed fish I filleted and chopped up in them and sat them in the coals to cook. Chopped a few ears of corn from the corn field sat them in the fire to cook. Excellent dinner. I couldnt have had a more peaceful evening with mother nature if I tried. Woke up this morning and fished some more but only got a few sunfish. Threw them all back but 1 I fed my dog with it. My KaBar still has a usable edge on it not shaving sharp anymore but still very usable. Swamp rat still shaving and slicing fine newsprint. I was going to strop it when I got home today but now I think I am going to wait and see how much longer it takes for it to dull to a non usable edge. I actually dont think I am in a big need for a 9" blade rat or ranger too quick now. This 6" blade did wonders last night. Oh yeah as I posted in another thread also found an old Buck missing its handles and rusted up but am going to repair it later.
 
I read this:

"I tried chopping till I felt I was going to die of heat exhaustion then I grabbed a pipe wrench out of my truck and pounded the living hell out of that swamp rat till I couldnt go any farther in and pulled it out and repeated. Took about 15 to 20 minutes to get it to go down but it went."

Can't stop smiling now - that's alot of passion, man!

THx,

MAT
 
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