BEYOND SHAVING SHARP - the edge magnified.

C

coote

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Apr 3, 2006
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I sharpened one of the knives I've recently made to shaving sharp. I then used if for a few simple jobs and found that it had lost its shaving edge.

Having a few idle moments, and being curious, I sharpened it to shaving sharp again on what I think is my finest stone....then looked at the edge through a powerful magnifying glass.

The edge looked awful!! It was uneven, and I could clearly see quite deep 'scratch' marks even though I'd used a fine stone. And I could even see what appeared to be a bit of minute 'folding' on a portion of the edge.

In practical terms, I guess this doesn't matter. In most real circumstances I don't have the time, inclination or equipment to produce a perfect edge. And I've used knives for years, for genuine jobs. I simply use the knife till it doesn't cut so well, then I give it a few licks on a steel or maybe use a stone first.

But what I saw today got me thinking. What if I got a smooth edge at the optimum cutting angle for the steel and the job at hand. Maybe the edge would last a whole lot longer. I will try to achieve this edge so I can play around with it, but I may need to get some finer abrasive...and a decent illuminated binocular microscope would be handy so I can see what is happing at the edge more clearly.

Anybody else got any thoughts on this?

Best wishes to all..... Coote (just heading off to work).
 
From my limited knowledge, I think that the blade edge can definitely become to thin, and those its edge quickly. Buy the "folding" edge is called a bur I believe. And it can be removed by "stropping" the blade. I'm sure someone else will jump in here with more details.
 
It sounds like a wire edge which fels very sharp but folds back or peels off with use. You can get knives to sharp or I should say to thin to have a durable edge. I use the EdgeMaker sharpeners and have for many years. They do about the best job of keeping a decent edge decent that anything else I have ever tried. At about 25.00 for the complete set, they are a steal. The Yellow one will hone about any blade to a scary sharp cutting edge. Plus its so easy that you feel guilty about having knives so sharp. NOT!!! NOTE, I have no connection to edgemaker. just passing the word because the work so well for me.
 
Well those people at Rockstead claim their edges are several times thiner than any other edge:

http://www.rockstead.jp/en/rockstead.html

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And that guy tells about his special sharpening process using 6 different stones, guess it is mostly marketing, yet polishing process is a large part of the making of traditionnal japanese sword.
http://www.watanabeblade.com/english/pro/togidashi.htm

As far as I know:
* toothy edge is better for soft materials (makes sense) so honed edge isn't as good for those
* honing/polishing reduces edge drag
* honed edge is less affected by shocks (makes sense too, since teeth on "saw edge" would probably get more easily damaged than a well "cohesive" edge)
* honed edge is better at push-cuts
* toothy better at draw cuts on the right material
 
coote said:
Having a few idle moments, and being curious, I sharpened it to shaving sharp again on what I think is my finest stone....then looked at the edge through a powerful magnifying glass.
Click to expand...

What is your finest stone? Try finishing using a 6000 grit waterstone.
 
Wow...some folks have gone into this quite deeply. Thanks very much for the links and the useful comments. It is all interesting....and good food for thought.

My finest stone is possibly the white standard stone that came with my Tri-Angle Sharpmaker, although I do have a brown Japanese water stone that is relatively fine as well. I have no idea of the grit size in the water stone.

I probably wouldn't have thought so much about this topic if I hadn't discovered Bladeforums.
 
Convex the edge a little with 1500 grit sandpaper and a mouse pad. 2500 grit works to,but takes a little longer.
 
I use a 2000 grit wet/dry paper on thick leather and for a final polish I use a leather strop with buffing compound. I wouldn't want to ever see my edge under a microscope... I MIGHT CUT MY EYE!!!!! .... lol. The edge lasts long and I haven't felt the urge to change techniques.

Looking forward to your findings......

Rick
 
Examining you edge under a magnifier is quite educational. The easiest and almost cheapest tool for this is a jewellers loupe; the ones that you can hold in your eye socket. These can be had in x10 and x20 - I use a x20. Only thing to watch with this is that the cheaper loupes have quite a short focus, so you need to hold the knife quite close to your face. Try not to poke your other eye out!

I use one quite often. When I'm feeling more adventurous (or not so lazy) I'll get out the binocular biology microscope I picked up cheap on the auction site. That really shows what's going on at the edge.

I strongly recommend anyone interested in getting the perfect edge (that's us knife nuts again) to try it out.

I find that I can get the edge quite well polished with a range of diamond pastes on paper, on either a leather back or an aluminium plate depending on flat or convex edges.
 
Ever since I posted that I wouldn't use a scope.... Its been burning in the back of my mind(a whole 2 hrs)...... damn you!! ..... damn you all to Hell!!!! .... time to scour the internet for jeweller's loupes and microscopes....

Why do I read these posts when I could just remain blissfully ignorant in the belief that I already know and bought EVERYTHING I will ever need?

Rick
 
Since starting this thread Ive ordered a special, relatively big, 30X magnifier from one Ebay seller, and a couple of jeweller's loupe magnifiers from another one. One loupe is a double...a 10X and a 20X combination, and the other is a 30X. This combination deal was amazingly cheap....something like $10 all up airfreighted from Hong Kong. And I used the 'buy now' option. If I had wanted to play around bidding I might have got something even cheaper.

I would have prefered a binocular-type microscope, but I didn't find anything cheap enough.

I reckon I might learn quite a bit from inspecting various blade edges. Considering that I've been using knives for decades, and that I'm a metalworking tradesman, it is a little surprising I haven't thought to do this earlier. But I have to say that really the only practical test that needs to be applied to a blade is to use it. If it does the required job, then it is OK. I suppose what I'm aiming for is a longer lasting sharp edge. I'm inclined to think that a smoother finish on the edge should help it last longer, but of course I'll have to test that.

Since I've started peering closely at the edge, the fine hone marks have started to look fairly coarse and deep.

Up till now, the best practical magnifier I've had is a 10X
 
Focal length vs. power

foxyrick said:
... Only thing to watch with this is that the cheaper loupes have quite a short focus, so you need to hold the knife quite close to your face. Try not to poke your other eye out!
Click to expand...

Yes and No. It's not actually the focal length, because focal length is inversely proportional to magnification. That's just physics. Here's the scoop.

Magnification=25cm/f where f=focal length (cm) and the mag is held at a fair distance (a few inches or more) from the eye. Note too that this equation is an approximation for many reasons, but for regular handheld lenses it works pretty well.

Now, if you move the lens(es) closer to the eye you begin to approach

Magnification=1+(25cm/f)

I have found that cheaper loupes tend to fudge a little on the magnification, forcing me to hold the lens and object closer to my face to get that extra 1+ magnification.

And for enquiring minds, an easy reference is:

http://en.wikipedia.org/wiki/Magnification
 
Well my new magnifiers haven't arrived yet, but I've done some further inspections with my little 10X loupe.

I've got a Dick sharpening steel. I use this often to sharpen both my kitchen knives and my outdoor knives. I can feel it 'biting' into most of my blades and it generally produces an edge I can shave hair with. Some folks might say that a steel merely 'straightens up' a damaged edge, but I have long suspected that it actually cuts (or abrades) the edge as well.

I ran a blade with a relatively smooth edge over the steel. The edge quickly became shaving sharp. I looked at the edge through the loupe and was horrified to see great rough channels cut into the blade. This sharpening steel (or the way I use it) is really quite agressive. It produced mini serrations.

I then ran this blade down the stones of my Tri-Angle Sharpmaker. I hoped to smooth down the edge a bit. After a few firm strokes I inspected the edge and could see fine metal 'filings' produced by the sharpening action, and relatively deep scratch marks.

Dang.... after years of sharpening knives I feel a bit shaken !!

I tried producing a really smooth edge using brass polish on a leather strop, but the process was too slow. I'm going to have to get a really fine stone or some fine abrasive powder or paper to achieve this I think.
 
What seems to be my best edge so far was produced this afternoon. I used my brown Japanese water stone (well the half-stone I got for free after it broke) to create the basic edge. I 'dragged' the edge backwards over the stone because of the imperfections in the stone. I figure that if I push the edge into the stone, it may catch on the imperfections and get damaged.

I'd tried stropping on cardboard earlier in the day, but I wasn't that impressed with the results. Perhaps I chose the wrong bit of cardboard. To finish the process I started on the water stone, I folded up some photocopy paper into a long strip and used that for a strop on the edge of my kitchen table. Not only did I get a shaving edge that would cut hair 'with' the lay of the hair on my leg (the usual test), I found that it would also cut hair going against the lay of the hair (but not quite as easily).

I then whittled half a willow shoot (cut for making an arrow) down till it was so small I could no longer hold it. The blade still shaved hair, but not quite as well....more cutting pressure was required.

I should add that this blade is only about 2.5 inches long, so it had to do quite a bit of work, relatively speaking, to reduce that arrow shaft to shavings.

Unfortunately, using the 10x magnifier, I did not notice any real difference before and after stropping on the paper (although this made a huge difference in the blade's ability to shave). Neither did I see any difference after I'd done the whittling. Maybe the new 30x magnifier will give me more insight when it arrives.

Gotta say though, even if I do come up with a way to produce a wonderfully smooth, durable edge....unless it is a simple, practical method that will work in the bush, I am unlikely to use it much. The old round ceramic rod, or even a small medium grit pocket stone or a small file are the only sharpening tools I generally carry.
 
Well I ordered the (2) loupe package from Ebay.... The set includes (1) double loupe @ 10x and 20x and (1) single loupe @ 30x....

Wasn't too much of a dent in the wallet

I guess this'll be the official "Loupe Review on Knife Sharpening" thread, eh?

I'll post my findings when I get the set.

Rick
 
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