Any idea what I am doing wrong?

[coyotes72]

I recently put a mirror edge on my butterfly knife and it would not cut paper. Before that, the finest sharpener that i used was a bare piece of leather and it cut great. I took the mirror edge off and it cut good again, but not as good as before the mirror edge, any idea what i did wrong? It has a convex edge, I don't know if that really effects anything though, thanks.


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[Obsessed with Edges]

The edge is likely rounded off by the mirror polishing, or slightly less than fully apexed. Convexing the edge may've also contributed to over-rounding the apex and/or leaving the apex angle much too wide. Make sure to raise a full-length burr (heel to tip) when sharpening, as that'll guarantee the edge is apexed. Then be very careful about cleaning up the burr without blunting or rounding the apex again.

Another possible issue: If your butterfly knife's primary grind is ground like many seem to be, i.e., a narrow & thick blade designed more for piercing/stabbing than for slicing, the basic geometry of the grind tends to be very thick behind the edge. If so, that will limit how thin the secondary edge can be made, and can make it more challenging to keep a very crisp edge on it. The apex itself is basically the only feature contributing to cutting performance on thickly ground blades like these; if it's not perfectly crisp, cutting essentially stops. Other more typical knives usually have the advantage of a thinner grind behind the edge, so the underlying geometry behind the apex is better able to contribute to efficient cutting, even after the apex begins to dull slightly.


David

 

[coyotes72]

So to get cutting performance back should I take the edge back to flat or something else.


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[Megabassx7]

Do you have a picture of your knife?
What David is basically saying is that you should go back to the stones or whatever you use to sharpen it to a convex edge and get a bur to raise on one side. Then repeat that process and work your way to finer grits and get that edge fully apexed.
Hold the knife with the edge facing upward toward a light and look straight down the edge. Is the edge centered on the blade? Does it look crisp and neat? If not you will again need to start from scratch and keep at it until you have a full apex. Try holding the blade at a lower angle if it's still not getting as sharp as you like. I have a feeling David hit it on the head when he stated the stock behind the edge was to thick. If that is the case you will need to work that bevel also

 

[bucketstove]

So to get cutting performance back should I take the edge back to flat or something else.

Hi,
You could simply add a microbevel
Take it back to your finest stones, and do 1-10 alternating passes at your final angle (re-form the apex)
or final angle plus 5 degrees (microbevel/deburr)
use as little force as you can manage , under 100 grams
use short strokes , about an inch of travel on stone
Try cutting (push/slice) newspaper
if you're satisfied with edge then you're done
if you're not satisfied, do another 10 alternating passes,
but check edge by cutting paper more often, maybe after each pair of passes
this should unround the apex and put the "tooth" back into it , should require less strokes by going +5 degrees

 

[Obsessed with Edges]

So to get cutting performance back should I take the edge back to flat or something else.


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That would be a good start. It'll eliminate the convexing as a possible cause of edge-rounding or leaving the edge angle too obtuse. Sometimes, deliberate attempts at convexing result in too much convex at the apex, because there's a conscious overemphasis on 'rolling' or otherwise pivoting the blade to produce it, or because the substrate used is too soft (mouse pad, for example) and rounds the apex via compression of the substrate. A natural freehand sharpening motion will always add a little convex anyway, even when attempting to produce perfectly flat v-bevels, because there's always some variation in held angle. If the primary blade grind is as thick as I assumed in my earlier post, you want to do everything you can to minimize any additional widening or rounding at the apex. Avoiding a deliberate convex is likely the better strategy for now.


David

 

[Chris "Anagarika"]

May I ask what is the brand or make of your butterfly? I have one cheap Chinese made, and the steel is rather soft, it works better at coarser finish.
I finished it at DMT EF at most. Anything higher it' loses the bite very fast.

 

[coyotes72]

It is a regal flipper from blade play, it has 440 stamped on it so it is probably 440a, I don't know how thick the blade is but can measure it. The primary bevel is hollow, and a few times when using the stones, I had tried to make the edge convex. I will make it flat again and go from there. Thanks


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[Rat Finkenstein]

it has 440 stamped on it so it is probably 440a

Chinese mystery steel.

 

[Obsessed with Edges]

It is a regal flipper from blade play, it has 440 stamped on it so it is probably 440a, I don't know how thick the blade is but can measure it. The primary bevel is hollow, and a few times when using the stones, I had tried to make the edge convex. I will make it flat again and go from there. Thanks


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'440' or '400 Series' is sort of a universal euphemism for unknown, generic stainless cutlery steel, most often seen stamped or etched on inexpensive imported knives. No telling what it's makeup is. As Chris mentioned earlier, steels like these often won't refine very well, because they're too soft (and there may be quality/purity issues too); that might be playing into the troubles as well.


David

 

[Corytr]

I'm in the 'just add a micro-bevel' camp for sure. If you add 5 degrees to your bevel, it won't take long at all to get it laser sharp while leaving the all of the hard work it took to get the mirror alone. Regardless of the type of steel, you should be able to get it to shave. How long the edge will hold up, that's a whole different conversation.