On Convexing, Thinning it or Re-V-ing it?

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sawgrass7

Joined
Nov 30, 2005
Messages
216
So me and my Ratmandu have had some serious woods time together and am lookin forward to more. I don't do any chopping concrete blocks, etc. abuse krap - I just use it outdoors and on back country trips. I freaking love it and it’s been good to me. Had it convexed years back when I learned about that and I liked it that way for awhile while it was really sharp but I’ve never been able to keep it sharp-sharp on my own.

I've watched the videos, etc. but my skills with the 'mouse pad- wet/dry sandpaper" thing haven’t yielded great success - and I never been much of a power tool guy. I got no time for water stones and been using Sharpmakers for 20+years for most my stuff. My old SRK has been with me all over north America and I can keep it n all my other blades plenty sharp. Except Ratbo.

So - should I find someone to thin the whole blade a little and then put a V-grind back on again? Is there any reason to not do that? Thanx guys
 
If your Sharpmaker works for you and all your other knives, stay with that.

Use the Sharpie trick to see where the Sharpmaker stone is hitting on the edge. If the edge is not getting sharp, you're not likely reaching the apex, which would be a common problem using the Sharpmaker to sharpen a convex edge.

You could have the blade reground so that it's thinner, but I'd do that only if you think you need a thinner edge for better slicing performance. If you already love this blade, you might not want to change it.

You could have someone put a 30-degree inclusive edge on the blade. Then use your 40-degree setting on the Sharpmaker to maintain a micro-bevel. That's the easiest way to sharpen.
 
For some reason I couldn't get the convex sharpening thing down, either, although freehand sharpening will convex the edge somewhat since it's impossible to hold exactly the same angle every time. I never liked what I thought was a fairly thick convex edge on my Battle Rat (9.5" blade; wood-chopping knife). I finally got the courage to grind it way down and eliminate the convex edge, but nervous it was going to be too thin for the dead and hard fir and pine I chop. Being the very high quality knife that it is, it worked out fine, although I am a believer in microbevels and put one on, just to be on the safe side.

I am not particularly recommending you do this to your Ratmandu. I'm not familiar with that knife and the BR is differentially hardened. Just letting you know I was happy with the results of the Battle Rat.

Personally, I think knife edges should be thin. I don't think it's debatable that thin edges cut better than thicker edges. If a knife doesn't do what I want it to do with a thin, or fairly thin, edge (and above the edge), then I don't want the knife. If I need a thicker edge then I'll use a good hatchet or axe.
 
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These knives are way too thick behind the edgr out of factory ,with stock thats too thick and grinds that serve better as prybars than a knife made for cutting.Most factory knives come this way out of factory and most of them have sub par heat treatment because with very thick stock less knives will break regardless of heat treat and also to save cost of grinding and heat treat.If you want to get a knife that cuts get a custom,or do your homework online and get a factory knife with decent ht and thin it out on beltsander first,then you sharpen it,as its really hard to find factory knife that has good stock thickess,grinds ,heat treat for decent price nowadays.I put all my knives to belt sander when brand new.Didnt have to do that with 2 customs that i have and very few factory knives.
 
I'd learn to sharpen it on a stone maintaining the convex and thinning it out over time behind the edge. Sandpaper over a conformable surface is not a good plan for anything but cosmetic surface polishing. Convex on a stone is actually very forgiving way to learn freehand.

Next step would be have it professionally thinned and re-V beveled.
 
Convex is easily done on stone,no need for sandpaper.Cheap belt grinder is also good idea,then just finish it up on st9nes and you can polish it with sandpaper in the end,then give it slight micro edge on stone.
 
Theres too much hype on convex grinds,especially thick ones,and some of these knives have axe like grinds that are more suitable for axe or large chopping knife,not a small 4-6inch fixes blades.Opinel sets example how convex grind should be done,also the blade thickness ,thinner blades cut better ,and thin blade with good grind and heat treat is combination hard to beat.
 
I wasn't having much luck with the sandpaper on a mouse pad until I went to using 320 grit wet/dry sandpaper.That got me close to what I wanted but still didn't cut hair so that was telling me that I didn't reach the apex yet,even though it felt sharp.I then splashed some water on my Shapton Pro 1k stone and ran a few edge leading strokes,making sure that my apex was just about to dig into the stone.At last,it was what I was looking for.
 
HeavyHanded, could you please explain why sandpaper over a conformable surface doesn't convex sharpen, or convex sharpen well? This is about the only way I've ever read and seen to sharpen a convex edge freehand, other than using a stone, and I've seen very little info on that.

HeavyHanded and lonestar 1979, I have read conflicting instructions and seen conflicting videos about convex sharpening with a stone. Would you please tell me how to do this?

When I freehand sharpen V-edges there is going to be some convexity because no one can repeat exactly the same angle every time. That being the case, is there any advantage to convex sharpening on a stone over V-edge sharpening on a stone, especially when a microbevel is added to the V-edge? I would think, especially with thin edges, that real-world performance would be pretty much the same with both methods.

lonestar1979, is the micro edge you mention a micro bevel or something else? I've never heard about a micro edge or bevel on a convex edge. Would you please explain further?

Thank you!
 
Thanks to all - you guys are great! Especially MtnHawk and lonestar
I grew up sharpening by hand on stones, carborundum to Arkansas, etc. and did great on my old school slip joints for years. As I graduated to solo camping around the country and wanted that trusty serious do-it-all sheath knife, especially in bear country I did fine with my choices. Then life got busy, oil stones became too much trouble and ceramic stones came out. And the current golden-age of blades n Kydex came into being. Ain't nothing wrong with my 1st gen CS SRK - yes, it ain’t full-tang but its done everything I asked of it. BK7, and a few others, too - all fine. No problems.
Only problematic blades are my sexy sharpened pry bars that feel so darn good in the hand, are solid works of American-made artistry and cut good. For awhile. I’m done with convexes. Sold my Fallkniven, too.

So lonestar - Thanks for backing up my gut feeling that I want the blade thinned just a tad so that like MntHawk - I can still use it to do hard-use stuff if need be. But still have that super cutting edge for 90% of my simple camp needs. I got zero shop skills and just want this darn Ratman sharp-sharp ASAP to get back into my rotation.

*Please tell me WHO-WHERE I can send it - to someone who understands all this exactly like you do and won’t fork it up? Cause I got no one I know. Thanks again - sawgrass
 
MtnHawk1 said:
HeavyHanded, could you please explain why sandpaper over a conformable surface doesn't convex sharpen, or convex sharpen well? This is about the only way I've ever read and seen to sharpen a convex edge freehand, other than using a stone, and I've seen very little info on that.

HeavyHanded and lonestar 1979, I have read conflicting instructions and seen conflicting videos about convex sharpening with a stone. Would you please tell me how to do this?

When I freehand sharpen V-edges there is going to be some convexity because no one can repeat exactly the same angle every time. That being the case, is there any advantage to convex sharpening on a stone over V-edge sharpening on a stone, especially when a microbevel is added to the V-edge? I would think, especially with thin edges, that real-world performance would be pretty much the same with both methods.

lonestar1979, is the micro edge you mention a micro bevel or something else? I've never heard about a micro edge or bevel on a convex edge. Would you please explain further?

Thank you!
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Make a bunch of Sharpie lines on the blade from spine to edge. Grind away, targeting first the region just behind the edge. Over time you want to blend this back unless it is already very thin, and they seldom are. I use a scrubbing pass when sharpening everything.

Then just sort of sneak up on the edge - with a convex, you can regrind the actual apex with about three passes on the cutting edge. Save the majority of the grinding for behind the edge. Think of it like a Scandi, except you have to shift the angle to hit the entire bevel.

Over time the thing will slowly flatten out to almost a FFG and that's where you should keep it - becomes extremely easy to maintain. I use this process with my camping hatchets and machetes as well. I should make a new video showing this as it comes up often - had some older ones but deleted them.

Sandpaper over a mousepad prevents you from deciding how you want the shape of your convex to develop - it is far more precise to do this by shifting the blade on the stone, or if using wet/dry it is the same thing - over a hard surface like another stone, glass, steel plate - you decide how the convex arc will develop.
 
You should thin the knife as Heavy Handed says,to slight convex,almost flat,thats a grind for a knife made to cut.Obtuse convex grinds are for heavy duty axes and prybars ,recently made popular by some companies and its just marketing hype.
 
Dont be afraid to use stone,you can polish the scratches out at the end and blend it in with sandpaper or finer stones.
 
lonestar1979 said:
Theres too much hype on convex grinds,especially thick ones,and some of these knives have axe like grinds that are more suitable for axe or large chopping knife,not a small 4-6inch fixes blades.
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Yes, great point and I totally agree! I think even a lot of axes, hatchets, and large chopping knives have edges which are much thicker than they need to be.
 
sawgrass7, you are welcome! I have been interested in sharpening for many years, and done a lot of it, yet am still learning from people in here that are more knowledgeable than I am.

You might want to take a look at the excellent book The Razor Edge Book of Sharpening, by John Juranitch. He writes extensively about relief grinds, which is what I think you want done with your Ratmandu. He writes very simply and logically and there are plenty of good illustrations and photos to supplement the text. It's good to learn about relief grinds and consider them a normal part of sharpening. If you just sharpen the very edge, the area above the edge may be thicker than it should be, which will decrease cutting performance.

I don't know much about convex edges but they don't have to be thick, although most of the factory convex edges I've seen are (see Post 9 above). I have a hard time imagining there could be much of a real-world difference between a thin convex edge and a thin freehand-sharpened V-edge, especially one with a microbevel.

I don't know anyone on the forum that does sharpening, but I'm sure there are many. Probably most of the knifemakers listed on the Forum page could help you out if you don't get some personal recommendations from this thread. Maybe Busse reprofiles their knives for customers. You might do a search for "professional sharpeners" on the forum, although I would still want some personal recommendations before I sent an expensive knife to anyone who isn't well-known and respected. It's easy to ruin a good blade by overheating on a machine belt or damage it in some other way. It would also be important to tell whoever you choose exactly what you want so they don't remove more metal than you want removed.

I relief grind all my knives, even the big wood-choppers, to a very acute angle and put a microbevel on. If the edge chips or rolls I'll play around with the angles to see if I can prevent that but don't want a knife if it can't perform well with a thin edge.

Good luck!
 
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The best method i've found to convex the secondary bevel of a blade is this one: sharpen free hand on a stone trying to keep a constant angle. If you are good at that you will get a V bevel; use your knife, resharpen it when needed still trying to keep the same constant angle, use the knife and so forth... After some sharpening sessions you'll have convex bevels.
When you try to convex a bevel the trap is to over convex it. Sand paper on a mouse pad or even on a glass plate will never be as firm as is a stone with the risk to over convex.

Dan.
 
Yes,after you sharpen knife few or many times,especially if stone is not flat you get convex,just have to watch its not too obtuse.Practice on few cheaper kn8ves,its not that hard,just practice.
 
lonestar1979 said:
Yes,after you sharpen knife few or many times,especially if stone is not flat you get convex,just have to watch its not too obtuse.Practice on few cheaper kn8ves,its not that hard,just practice.
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I was worried about sharpening a convex grind knife prior to my buying one and a man who sharpens for a living told me to just use my Waterstones and sharpen it like I would a flat grind. Now it makes sense to me since it is usually difficult for me or most people to hold that same angle throughout the progressions. So eventually, I will be maintaining my convex edge or creating a new one.
 
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