sharpening?

P. McKinley said:
Flat edged blades I'm fine with. As a chef you learn this skill on bench stones.
What I struggle with is sharpening aggressive re-curves. Currently I use my 1/30 grinder with a variety of belts finishing with a leather honing belt and get pretty good results, not great. I don't have a rod-based system which I believe would work, but I'll bet very few of my customers have one either, or a grinder and belts. If I'm going to do re-curved blades I'd like to be able to sharpen then in a manner that can be done by its future owner.

So, how would/do you sharpen a re-curve without rods or grinder?




-Peter
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If the bench stone isn't too wide you could use that too. Keep the same angle and make sure that every point of the curve you are sharpening is perpendicular to the stone.
Alternatively get non bench stone and move it along the edge while you keep the knife fixed.

Nice knife btw:D
 
I take most my blades in grinding to where they are almost sharp, then on my 2x72 I use a bubble jig to set the angle, such as 20*, and use 120 belt a couple of times on one side then the other and form a burr, move to 220 and using the angle set by the bubble jig do both sides until a burr is formed again.

I then go to a 1x30 laid on its back with the belt moving away and use a leather belt with green compound and a couple of quick passes and it is sharp and has a great working toothy edge.

The bubble jig is key for consistency in maintaining the chosen angle. A light touch is key throughout the process.

Like anything else it has to be done properly. There are those who are to heavy handed and should not use this method and should stick with stones.
 
Jens, if I get Your advice correct, I think it's in my line of thinking for sharpening knives (the BM 710 I recently bought)- I wasn't too comfortable with the idea of using the edge only of my Spyderco DoubleStuff for the recurve, so I bought Spyderco's fine round stone/file for 'rougher' work on it and am planning to get ultra-fine Sharpmaker (triangular) rod to be used on all my knives (flat side on normal edges and edges for recurves)... IMHO the trouble with recurves is the 'tilt' angle changing in the recurve bit and the only way to get it 'right' is to have stone to blade contact in one point rather than over certain length as with normal benchstones and conventional blades (which require 'tilting' the blade only upwards and not downwards as well)... If I was a knifemaker I'd think the best way to establish the bevel would consequently be on a small radius grindstone or some sort of pin wrapped in sanding paper.
 
Wolf_HR said:
Jens, if I get Your advice correct, I think it's in my line of thinking for sharpening knives (the BM 710 I recently bought)- I wasn't too comfortable with the idea of using the edge only of my Spyderco DoubleStuff for the recurve, so I bought Spyderco's fine round stone/file for 'rougher' work on it and am planning to get ultra-fine Sharpmaker (triangular) rod to be used on all my knives (flat side on normal edges and edges for recurves)... IMHO the trouble with recurves is the 'tilt' angle changing in the recurve bit and the only way to get it 'right' is to have stone to blade contact in one point rather than over certain length as with normal benchstones and conventional blades (which require 'tilting' the blade only upwards and not downwards as well)... If I was a knifemaker I'd think the best way to establish the bevel would consequently be on a small radius grindstone or some sort of pin wrapped in sanding paper.
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Yep. You described it better.

I'm not a knife maker but am working on my first one. I didn't pick the easiest blade shape but it's going well. To get the re curve I use the belt grinder where the belt bends over the spinning cylinder. I make sure the point of the curve being ground points perpendicular over the cylinder. Thus I can't just swipe the blade straight left and right but constantly adjust it while moving it. Sounds complicated but comes quite naturally.
To get a consistant angle I just use my eyes and try to keep the same gap between spine and grinder. Of course that only works as long as the blade shape has the spine parallel to the edge.
 
Bill DeShivs said:
It puzzles me how knifemakers can't sharpen knives without jigs.
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I can sharpen using a half dozen techniques, some resulting in a convex edge, some resulting in a flat edge, some using a fixture or jig and some not. The OP's interest was in how to sharpen an edge so as to end up with, not only a sharp edge, but to do it consistently and accurately. Using a jig will many times be the best way to accomplish this. The same goes when the goal is to grind identical blades, its much easier to do using a jig or fixture. Its faster with fewer corrections. There's nothing wrong with free handing and there is nothing wrong with using a fixture or a jig. I use jigs on my mill, at my welding station, at the forge and most other places in the shop. We are all different in how we learn and how we use our skills, there is no right or wrong to it.

Regards, Fred
 
Jigs are used to sharpen drills, endmills, saw blades and any thing that is used for precision cutting.

Look at it this way, some people like to use a meat jig and others use metal ones.
 
AVigil said:
Jigs are used to sharpen drills, endmills, saw blades and any thing that is used for precision cutting.

Look at it this way, some people like to use a meat jig and others use metal ones.
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Don't want to derail anything buy what kind of bubble jig do you suggest for stock removal with bench disk grinder and belt grinder and how much do they cost? Thank you.
 
I'm just starting out and learning. After asking the same question and investigating I decided to go with Japanese water stones. I went with a murray carter purchase. Honestly I'm struggling with the 6000 grit finish stone. Today I received some Tomek honing compound from tru grit. I used it on a leather strop and it worked like magic! I used this strop in lieu of the 6000 grit water stone. Blades came out hair shaving sharp. I finally overcame the strop hurdle. :-)
 
I used to use the wicked edge system. WAY to much time for each knife. I decided to give the slack portion on my 2x72 a try. Couldn't believe how easy it was freehand. On 154cm I start with a 220 grit then move to trizact. On simple carbon steel I just use the trizact. About 3-5 minutes to set secondary bevel, once I see a burr the length of the blade I lightly buff the burr off and give 10-15 stokes on the leather strop. At that point I cut a piece of paper. It is easy to feel any spot that is not sharp by slicing it thru free hanging paper the full length of the blade. If there are no drag spots I give a couple more strops and it will easily shave at that point.
 
There are many ways to skin this cat ;) "meat jig"... heh! :thumbup: As long as you don't overheat the edge, or pull a huge gnarly burr off it that will just flop back and forth all day and annoy you, there's not really a "wrong way" to sharpen.

Typically my edges are pretty thin, so it only takes a few passes (edge up) against an A45 Gator belt to set the edge bevels and just start to raise a burr. As mentioned before, I do this on the slack portion just above the platen, and use very light pressure, so as to help keep the edge cool but not convex it (you can always roll the shoulders back once the edge bevels are set). Then I switch to a 400/1200 EzeLap combo diamond plate to clean and refine it, strop on plain leather glued down to a board, and call it good. I find that for most knives, this provides a crisp but slightly toothy edge that cuts well in a variety of tasks. For more delicate, task-specific blades I continue with micron polishing belts and/or higher grits of wet/dry sandpaper and 3M polishing sheets, leather with fine polishing compound, etc.

One sharpener who specialized in chef's/sushi/sashimi knives told me his "secret weapon" was Mother's chrome polish on a hard backing as his final step.

One thing I've found about stropping is that if it takes more than a few strokes per side, or I have to apply pressure... either I wasn't really done on the last stone, or I raised way too big of a burr to begin with.

P. McKinley said:
So, how would/do you sharpen a re-curve without rods or grinder?
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I just use hand-held, narrower stones/plates, like the "pocket size" ones roughly an inch wide. It's not a big deal, it just takes longer. The even narrower stones in Lansky-type systems also work well inside those curves, as I'm sure a rod-type system would. You might be surprised how many users do have those sorts of systems, so I wouldn't worry about it too much.
 
Thanks for the input guys, I used my grinder again last night with actually much better results. I just made a flat platten for it not too long ago, so this was the first time trying it on the belt above the platten rather than my 10"wheel. So maybe the angle of the belt before is what was giving me the trouble. Still room for improvement, and I'm going to try some of the other suggestions as well. Thanks again
 
Fascinating feedback. I have a Spyderco system and also got a set of diamond grit triangle stones. They cut aggressively .
Today I just purchased a WickedPro system. I looked long and hard at the edge pro but in the end went with the wicked edge. Now I just need to wait for a week until it arrives
 
Actually i think there is a wrong way to sharpen...it is on a dry belt grinder. the fastest way to ruin the temper of the edge. The actual edge just has no mass to dampen the extreme heat from friction and tranfer it to the rest of the blade.
Here is a site that is very interesting for sharpening fans :) https://scienceofsharp.wordpress.com/
Understanding what happens at the apex scale is what helped me improving my sharpening skills, that and...messing with straight razors ;)
 
I think some folks see sparks from sharpening on a belt and assume that it means the edge itself is over heated. Not true: small particles of carbon rich steel will burn spontaneously if suddenly exposed to oxygen (i.e. sanded off).
Keep the edge off (just above) the platen, use light pressure, sharp belts.
Another tip is, don't make a pass all the way from choil to tip, the other direction is better- you'll see much less heat buildup in the tip if you do it first, moving from tip to choil.
 
Actually has been tested with micro TC probes buried inside, hand rubbing a block of steel over a 1000 grit paper, the very surface reached peack temperatures in the range of 2000 °C....quickly adsorbed by the huge mass of the block. Also micrographs showed white untempered martensite in the skin of a grinded piece as a result of AUSTENITIZATION taking place during grinding, "quenched" by the steel mass itself. You may want to go and search some posts by Roman Landes on the subject, very interesting. Or you could read the interesting discussion here: http://www.hypefreeblades.com/forum/viewtopic.php?f=3&t=391&hilit=sharpening
I have never seen a spark, by the way, no hand sanding neither filing, even if said small particles are produced.
I don't say you can't grind an hardened blade (even if i do it under coolant) and throw some sparks, when you have still enough "meat" to adsorb that heat without much issues, but when it comes to sharpening the very edge you really have to know that the thin apex is going to need a lot of care. Grinding is a different from milling, there you remove the chips bearing the heat...in grinding abrasion take places and heat is transfered to the piece if there is not coolant.
 
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Time and temperature is what is important

not just the temperature.


otherwise our belts would burst into flames :)

Doing something correctly makes all the difference with the end result.


It is rather interesting to see Ruana Knives who have turned out thousands of knives since 1938 ,and have a good reputation as to holding an edge, puts an edge on their knives with a grinding wheel with sparks flying lol

https://youtu.be/lBKnLe7tYmU?t=8m58s
 
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