Sharp Thoughts

  • Thread starter Thread starter db
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Cliff,

When db said "wide", I think he meant from edge to top of had-to-be-added relief grind, not top of said grind to top.
 
db said:
...by hand sharpening and thinning the knives I have I end up with a pretty wide convex edge bevel.
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The alternative is to bring down the primary grind, more efficient in the long run but not practical with hand stones. However once you do adjust the primary grinds on a few knives then really wide edge bevels won't look so attractive anymore, as not only do your knives now cut better, the edges are more durable and can be restored from heavily used to optimal sharpness in less than a minute.

[really coarse belt]

frugalweaver said:
To say that is sharper than a properly shaped and finished edge is a stretch.
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An optimally sharpened edge should give maximal cutting ability and edge lifetime, a really coarse belt finish does that for some tasks, the best I have seen is 100 grit AO, Chad E. reported 80 grit AO is a better rope cutter still. Some makers are known for coarse finishes, Dozier for example leaves a very aggressive edge on his knives, Phil Wilson like the coarse SiC norton hone for rope cutting. It just depends on what you want to do, sharpness like most aspects of knives is use dependent. I tend to prefer high polishes, but that is because all of my current EDC knives have extreme edge profiles and I do little actual slicing.

If it works it works. My brother used to sharpen knives on shingles at work (carpenter). Yes it tore up the blades, and yes he used to do it to the really high end ones I loaned him, but it kept them cutting and cutting aggressively which is what he needed and I really don't care what they look like and he knows that. A highly refined ultra-polish would have not cut as well for as long, and would have taken far longer to resharpen than a few really hard passes on a shingle. You really don't have time to stop and restore a blade with a series of stones, and a simple stropping doesn't work when you are cutting fibreglas insulation.

-Cliff
 
If you have a all round knife and use the knife for all types of work, the sharpening angle can be something like 22-26 degrees, straight or convex is a matter of taste. I prefer convex edge for this type of knife.

If you have a knife specially and only for woodwork, the angle must be exact. 19 degrees is a nice angle for soft wood and 22 degrees for hard wood. It is also a matter of “taste” if you use 19,5 or 20 degrees for softwood, and also a matter of how much power you like to use.

So, the answer depends on what you are using the knife for. All round knife, the angle can change, a knife you use for cutting in wood, the angle must be exact.

Convex edges cuts better in nearly all material then a straight edge do, but not in wood. If you work with wood, use straight edges with perfect angle along the blade.

Many people discuss type of edges, straight or convex and what type of edge is the best. It is also depending of the use of the knife.

Axes with straight edges, we call the carpenter axes, is for cutting along the wood fibers. Axes with convex edges is to cut across the wood fibers and also splitting wood.
If you use a straight edge and try to take down a tree, the axe fasten in the wood, a convex edge do not fasten, it bums out again - if the curve on the convex edge is ok.

If you try to use a axe with convex edge as a carpenter axe, you must hold the axe in a angle that the power from the stroke goes in to the wood and it can spoil your work. With a straight edge, the angle of the axe make that the power goes downwards, in the direction of the edge, and cuts out a fine slice of the wood.

The sharpening angle of the edge of knifes works similar. For wood work you must come close to the wood. Compare with a plain steel angle.

Some of the oldest knifes have chisel edge. That means that there was different knifes for left and right handed people. With that type of edge you can use your knife as a plain steel. Other knifes have 15 degrees on one side of the blade and 5 degrees on the other side. The edges was design for the purposes of the knife.

Then, some blacksmith start to produce knifes in industrial scale. Why do different knifes for left and right handed people? He put the edge in the middle – one type fits all! It works nice today because we have got use to that – but we do not work so much in wood at they did before.

Thomas
 
Thomas,

Great post concerning the merits and applications of edge types. Thanks.

I'm not certain that centered edges are an appeal to ambidexterity, probably more to do with a universal enjoyment of symmetry and the growth of machines allowing our knives to be used for more leisurely and less purposeful tasks. Off-centered edges abound in certain culinary and many woodcarving collections.

db,

I tried using the sharpening technique you posted on a recent thread. Not having waterstones suitable for use outside of my EdgePro, I placed my Sharpmaker upside down on a towel and placed the two medium hones in the slot on its underside. A curved was sharpened, so only one hone should've been used, but the difference in finish it left was much brighter than when using the preset angles and pressure appropriate for such angles. Likewise, the hones quickly loaded with steel and needed help from a rust eraser. Anyways, what a great technique! Thanks for sharing that link!
 
Thom you are welcome. Glad to help another move to hand sharpening. Your different results from useing the Sharpmaker as a bench hone rather than the v system is interesting. I'm going to have to think about that before commenting on it more.
 
If you still have your Sharpmaker and have access to a towel or a non-slip mat, you can do it, too. The difference was twofold:

1. Used a less than 15 degree angle, so there was a larger surface area.

2. Able to apply more pressure to blade against hones than when less than an inch of the hone is sitting at a 75 degree angle without straining plastic base.
 
Both sound reasonable :) I don't have a Sharpmaker anymore. Just another thought another benifit to water stones is they don't clog up so much or as fast.
 
Reading "angles don't really matter" spurred me on to try and sort my burgundy CJ out. After some time with a diamond stone keeping only roughly the same angle (I reckon about 20° inclusive, maybe?) I put a 30° microbevel on with my sharpmaker browns. This knife is CRAZY sharp now.

I was only barely trying to keep the angles correct with the diamond stone yet I am most impressed with the edge I have created. I suppose it's more about the edge than what's behind it?
 
daverave999 said:
I suppose it's more about the edge than what's behind it?
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Kind of. Some folks, for their craziest-sharp edges, will make the area leading up to the edge as polished as possible just in case. Others just make it 'very thin - more or less' and then make their edge as small and polished as possible. All of it works to some extent or another. My knives that cut things around the house and open bags and sacks tend to be as sharp as my skills and toys allow and my knives used for other forms of entertainment need only be hair-popping sharp.
 
Daver, good for you. Well, yes what is behind the edge does matter as it can effect how it cuts. Thinner/polished will have less drag. And sharp is for the most part right at the edge tip. You can have a very sharp thick edge that doesn't cut real well. It sounds like you did a good job at thinning down the edge then putting the finnal edge on with the Sharpmaker. Good job. Funny how easy it is isn't it? :)
 
daverave999 said:
I was only barely trying to keep the angles correct with the diamond stone
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You don't need to be precise with shaping, you are just hogging off metal. You will notice a massive difference in ease of sharpening with a microbevel of 15 on 10 vs 15 on 15.

-Cliff
 
db said:
Funny how easy it is isn't it? :)
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Yes, quite frankly! I can't help feeling it would have taken years just on the ceramics though. I certainly feel more confident that I can take a knife to a benchstone now.

Cliff, it only took a couple of strokes per side after the stock removal. I had been going at it on the brown corners at 30° for a few weeks :rolleyes: but seemed to be getting nowhere. I was using a cheap 150 grit diamond hone this time and it took less than an hour.

Is it worthwhile bothering to polish behind the edge? Could I get away with just stropping to achieve this?

Apologies for the slight hijack.
 
daverave999 said:
Is it worthwhile bothering to polish behind the edge? Could I get away with just stropping to achieve this?
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Polishing behind the edge will reduce drag and make push cuts easier. Stropping may help over time, but with the more popular stropping compounds being over 9,000 grit and your diamoand hone being 150 grit, it may take a while. If you use the chisel section of your Sharpmaker base and the medium hones, the relief grind will polish right up.
 
Daver yes it probably would have taken alot longer just useing the ceramics. I always do a little polishing behind the edge. Like Thom says a few good passes with the Sharpmaker should be good enough. I'm not sure it's really a very big difference if you do it or not, however I do notice I get less sticky tape goo and stuff if I polish it up than if I don't. So at the least it is a little cleaner. I don't think your hijacking the thread. :)
Seems to be very much on topic angles, grits, backbevels, free hand, and jigs all seem related to me.
 
Polishing behind the edge is ok if you like to have a pretty knife – but is not ok not for all knifes if you look at the knifes performance.

When you cut fresh meat, the meat fibers is “glowed” to the knife and is following the knife when it is moving. This because there is about 65% water in the meat. The water “fasten” on polished surfaces (I do not knew the correct word for this in English). You knew, when you fill water in to a cup, the water is going about 1 mm over the edge of the cup? The same function have water to “glow” polished surfaces.

A good hunting knife shall not be polished, it shall have a lot of “scratches” on the sides of the blade. The scratches is stopping the water to “glow” on to the blade and the water, and the blood is functional as oil in a engine, and the knife cuts better in fresh meat. The meat fibers is not following the knife when you cut.

Scratches have a important function on this type of knife. It is not nice looking, but the knife performances are much better.
So, when you se a hunter shaving him self and use the knife as a mirror – you can recognize that this is not a real hunter…

Thomas
 
I think your refering to water beeding. I personally haven't noticed any lak of performance do to a polish behind the edge. I think you have some very interesting points I haven't thought about.
 
Not sure about water-beading. Sounds like adhesion and possibly the vacuum of a relatively fresh carcass.
 
Surface tension of water on a polished surface. Bead blasted is a better surface because it cuts surface tension without adding extra drag of a highly scratched surface.
 
Well, it is rather easy to test it. Just find two mouse, about 500 kilo each, shout them, skin them and then use a polished knife on the first one and a scratched knife on the next. Measure the time to slaughter them and how tired you are after each one of them.

Perhaps it is easier to test on a cucumber? Did the slices “glow” in the scratched blade?

Thomas
 
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