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 Post subject: Re: Sharpening convex 3V
PostPosted: Sun Jul 07, 2013 1:59 pm 

Joined: Thu Jul 04, 2013 2:33 am
Posts: 6
Hi Ken, you are excused :D

"Of course", I "need" a screaming scary sharp blade ;) Nevertheless, a reasonable use of field should be achieved, also the ratio of costs and result.

Jason has represented with his post, that he would not not go below 1 micron, because it will reduce edge retention.
Should I defied Jason opinion, the next reasonable step would not be 0.5 micron, rather 0.25 micron, is that not a too big step :?:
Thereof regardless, in your experience, 9 micron for the blade "out of box", as well as for the slightly dull blade is a good start.

Kangaroo strops or Nanocloth, which is more compliant and follows better the convex blade :?:
Should be used for a thicker blade (e.g. Bravo 1), a thicker leatherstrop :?:

Guess while stropping, the weight of the blade is enough, or demand the used, presumably somewhat harder strobs additional pressure :?:

Ken, thank you for your kind contribution.


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 Post subject: Re: Sharpening convex 3V
PostPosted: Sun Jul 07, 2013 6:51 pm 

Joined: Tue May 29, 2012 12:29 am
Posts: 793
The difference in edge retention from 1 Micron to .25 Micron and finer would be a moot point, most things such as cutting paper are coarse enough to disrupt a edge at that point.

I don't think your reading between the lines though, Ken is not saying sharpen your knife to 640k but rather that its possible. The 9 or 15 Micron CBN that he mentions would probably be a good starting point. I have some 15 Micron myself and agree it works very well to keep a nice level of sharpness to a knife in use.


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 Post subject: Re: Sharpening convex 3V
PostPosted: Mon Jul 08, 2013 4:05 am 
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Well 15 microns is equivalent to a 1000 grit finish, so certainly I wouldn't find an edge coarser than that what I would like. If you need to touch up an edge in this 'shape' it is certainly reasonable to start there, but I would suggest keeping your edge at a higher level of finish than that. Personally, I'd keep my edge at a 2 micron or 8k level of finish - at least. If you HAD to pick just one grit I'd suggest 2 microns for general use. From there you can expand up or down for your needs. I'm betting you will go finer :)

Now if you go to 1 micron and wish to go further you could go to 0.5 microns or jump to quarter micron. You'll find the CBN is pretty aggressive for it's grit level so 'jumps' aren't that unreasonable even for 3v.

What level to go to? Well if you are batoning trees all day long (I'd use an axe), less refinement is reasonable. If you need it to do more delicate tasks - skinning, preparing food, etc, I prefer a more refined edge. I also find edge retention not that big of a factor if you just keep things sharp rather than letting things go longer. Ultimately this becomes a set of choices based on your needs and habits. "Keeping an edge sharp takes very little work". Given 3v's high edge retention I'd 'push' it to see how fine of an edge works for you. You would do well with either 'roo or nano' as a strop. If portability is an issue, consider the 1x6" or 2x6" form factor. If you are doing your tuneups before going 'out', consider the larger 3x8" size.

The issue of keeping a convex edge sharp isn't really sharpening the entire convex curvature, but just the 'edge of the edge'. This can be done with a hard strop by determining the angle at the edge of the edge and just sharpening there.

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 Post subject: Re: Sharpening convex 3V
PostPosted: Mon Jul 08, 2013 7:25 am 

Joined: Thu Jul 04, 2013 2:33 am
Posts: 6
Dear Ken, thank you for your great explanations and recommendations :!:

Also, your last sentence sounds catchy, but my feeling (free of any practical experience) says, with your procedure, finally I get at a microbevel, and then it might be difficult for the inexperienced to get rid of this.


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 Post subject: Re: Sharpening convex 3V
PostPosted: Mon Jul 08, 2013 10:19 am 
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Ah this is too interesting of a question not to come back to the computer and write a response :)

So if we have a convex edge the angle is changing all the way to the edge of the edge. It truth, if we freehand, even attempting to do a flat grind we produce an edge that is somewhat convex. Now if we take this convex edge and place it against a strop - kangaroo or nanocloth for instance - at a very acute angle and GENTLY do an EDGE LEADING stroke into the strop, it will not 'catch' until the angle is steep enough. So starting at a very acute angle, we gently do an edge leading stroke gradually increasing the angle until it 'catches' and STOP going forward so as not to damage the strop. You have now determined the angle of the edge of the edge of your convex edge.

Now go to the end of the strop and KEEPING THIS ANGLE, do edge trailing strokes. Now you are working the edge of the edge. Let us call this angle angle X.

This is different than putting a microbevel on a convex grind as one typically does the microbevel at a more obtuse angle.

In an even more subtle way, one can strop with some variability UP TO this angle X using it as a sort of line not to exceed. So we are attempting to not change angle X, but rather to refine it's surface characteristics to a finer level of finish.

Now if we wish even greater subtly, we can work this edge with a variance not just up to angle X and never exceeding it, but just a bit more acute than that. Calling this difference DELTA, you would describe the angle at the edge of the edge as approaching 'X - DELTA'. This is effectively 'microthinning' the edge of the edge, where we work the edge at this slightly more acute angle until we reach the edge of the edge. Now we have actually changed the radius of curvature to a slightly decreased radii.

The short version of this is that you don't have to put a microbevel on the convex edge to further refine it, but can preserve or alter it as per your requirements.

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 Post subject: Re: Sharpening convex 3V
PostPosted: Mon Jul 08, 2013 12:10 pm 
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It's a bit difficult to catch but watch this video at about 58 seconds on my facebook page, https://www.facebook.com/ken.schwartz.984 , for a few more seconds to see this technique of coming up to a certain angle but not exceeding it. At first glance it looks like just unsteadiness, but it is quite purposeful and precisely executed over the entire convex surface of the knife.

https://www.facebook.com/photo.php?v=56 ... =2&theater

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 Post subject: Re: Sharpening convex 3V
PostPosted: Tue Jul 09, 2013 1:00 am 

Joined: Thu Jul 04, 2013 2:33 am
Posts: 6
Hi Ken, I have seen your youtube video, looks easy..., guess the craftsman is an artist on the grinding belt...


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 Post subject: Re: Sharpening convex 3V
PostPosted: Sat Jul 13, 2013 2:19 pm 

Joined: Thu Jul 04, 2013 2:33 am
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Ken, one more question to reach "your" angle "Delta X": Which micron should be used to achieve these sensitive angle "Delta X"?
Probably not with the full micronrange, rather with the micron, which ensures the desired final sharpness, so 2 micron down to...


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