Kershaw Rake factory angle :confused:

Razorsharp-Travis said:
i use 17 or so degrees on my hard users, used a chopper at 19, used a machete at 17..... 20-22 for my axe.........30 for my imaginary ceramic chopper.... nobody should need to use 30 lol
Click to expand...

I don't think he needs 30, but from the sounds of it his factory edge was even greater than 30. I always take an iterative approach to improvement, and was merely suggesting that he do the same. 30 would be an improvement over the factory edge, and for all we know it may be good enough for the OP. If it isn't I would step to the next angle, then the next, etc. That's why I said I'd start there. I apologize for any misunderstanding, it's just my personal view on process improvement. Baby steps :)
 
bpeezer said:
I don't think he needs 30, but from the sounds of it his factory edge was even greater than 30. I always take an iterative approach to improvement, and was merely suggesting that he do the same. 30 would be an improvement over the factory edge, and for all we know it may be good enough for the OP. If it isn't I would step to the next angle, then the next, etc. That's why I said I'd start there. I apologize for any misunderstanding, it's just my personal view on process improvement. Baby steps :)
Click to expand...

Like I said, the hardest use my knives see is food prep, opening packages, and very rarely cutting a box or 2 in half to make them fit the recycling bin. I figured since I'm going to be reprofiling the edge I might as well go all out. It's taken a looong time to reprofile. I actually haven't gotten back to it since last week. I'm thinking one more session with the extra coarse diamond stone and I'll hit the apex. Then I'll start refining it with the medium and fine diamond stones and finally the ceramic. Hopefully I can get an updated picture by the end of this week.
 
blame it on god said:
I disagree. I sharpen at 20/25 degrees all the time and it is still shaving sharp. I started sharpening at those angles because I got tired of stropping my Cold Steel knives every time I used them. 25 degrees per side may not be "tree topping" sharp but it is still good utility edge and is much less likely to deform.
Click to expand...

You can, but you are wrong.

I said nothing about how sharp something can be but how long the edge will last at a given angle.

Like my quoted post says, if you sharpen at 50 inclusive you are fighting the thickness of the blade to cut due to poor bevel geometry. In use sharpness at this angle will also decreas with extreme speed due to the geometry.

I'm not making this up, its all factual.
 
knifenut1013 said:
You can, but you are wrong.

I said nothing about how sharp something can be but how long the edge will last at a given angle.

Like my quoted post says, if you sharpen at 50 inclusive you are fighting the thickness of the blade to cut due to poor bevel geometry. In use sharpness at this angle will also decreas with extreme speed due to the geometry.

I'm not making this up, its all factual.
Click to expand...

I think I understand what you're saying. The narrower the angle, let's say 10 degrees per side, the faster it will dull. The same happens with a wider angle, let's say 35 degrees per side because the edge is so flat that with only a little more wear it makes it not sharp at all.

I hope I explained what I meant well.
 
You got it.

It's a balancing act of not being too thin or too thick. Thin is always better though because even after its dull the geometry still slows it to cut, basically the reason a convex grind seems to stay sharper longer.

So, to rephrase. Once the sharpness is gone from a edge you are left with a flat steel face, the more obtuse your angle the larger this face becomes. Dulling creates a exponential growth of the apex width, so a more obtuse bevel will dull at a faster rate than a thinner one.
 
knifenut1013 said:
Dulling creates a exponential growth of the apex width, so a more obtuse bevel will dull at a faster rate than a thinner one.
Click to expand...

I would have to assume that, as long as you have perfectly consistent bevels, apex growth would be a linear function, not an exponential one. Not trying to say you're incorrect about it though, when it comes to sharpening you really know your stuff :)

How is "dulling" described? Is it volume of material displaced? Distance from the original tip? Width of the new apex? Rate of growth of the width of the apex with respect to distance from the original tip?

I'm having difficulty finding a definition for rate of dulling or something along those lines. By any of my definitions though, you are absolutely correct that a wider angle dulls faster. Just not exponentially so ;)
 
I'm not the best at math but the rate of apex growth happens on the slope of a triangle so I would be guessing its exponential.

Edge wear is just that, the edge when cutting is experiencing abrasive and compressive forces that will reduce its mass and deform its shape. You could measure dullness/sharpness by the width of the edge apex.
 
Thanks for the info! Out of curiosity, have you ever measured the width of an edge before sharpening? I'd be interested in finding out an approximate rate of material removal for stuff like this :)

Also, growth along a triangle is considered linear growth. For reference, exponential growth curves upward, sort of like this:

Exponentialgrowth.jpg
 
I would too, wanna fund my scanning electron microscope? :D

I think I said that wrong, its not that the dulling happens on a slope but the top of the bevel which is basically a triangle is removed so now its twice as wide. It wouldn't increase by a single factor because the increase is headed in two directions from the apex to the bevel shoulders.

Am I still confused here or is that correct?
 
The width of the edge could be described as 2*x*tan(theta), where theta is the angle per side and x is the depth of material removed from the original edge. Since theta stays constant, the only variable is x so the width grows linearly :)

For example, if you abrade a depth of 1mm and the blade is 30 degrees per side (I know the angle is ridiculous, but the math is easy with it), then the new width of the blade will be 1mm (grows by 0.5mm per side). If you abrade away 2mm, the width will be 2mm (grows by 1mm per side). That would be growing by a width of 1mm width/mm depth (not realistic at all, but should describe my point I hope).

Also, I really hope there's a cheaper way to measure the width than an SEM, because if not I'll NEVER get to measure my edges :rolleyes:
 
Thanks for the explanation, linear it is :)

Yeah, with edge widths at 1 Micron and less its going to be hard to measure without one.
 
I agree that a more acute edge in the same steel (being reasonable) will stay sharper longer.

When you push, or slice an edge through media there is more resistance (abrasion against that steel) to an obtuse edge. Of course I may just be saying what's already been said. I'm tired. :o
 
I drew up a quick diagram to show what you mean knifenut:
On the left there's a narrow angle edge and a wide angle edge under it. If the knives dull the same amount(purple bracket), the blade with the wider angle gets a wider flat edge than the lower angled edge.
acutevsobtuseangle.jpg
 
You must log in or register to reply here.
Back
Top