The Bleeding Edge

[Art]

The Edge. The business end of a knife or cutting tool. The perfect edge occurs at the intersection of two planes, which are the sides of the knife that intersect each other; the perfect edge formed by the two planes would a one dimensional line of zero radius. This is just not attainable, because the planes are made of something whose molecule has a radius, and where they intersect an edge is formed by at least a single molecule that has a radius. In practical terms, this ain't a going to happen. Maybe in a lab, maybe. But there is a downside, it is a fragile edge that won't hold up and will round over to the point that it is less sharp but more durable.

That is the scientific claptrap. Our best edge is going to be rounded to the point that you and I can see it with a loupe. I have four loupes, a 5x, a 10x, a 20x, and a 30x, and some comparator scopes that go way beyond that. If I take a brand new Irwin Utility knife blade out of the box and look at the edge under 5x, I can see the edge. At 10x the edge is obvious, and a 30x it looks like a landing strip. Quality scalpels are somewhat better, but still a highway at 30x. Quality of the plane grinds (facets, bevels) and polish are an important in attaining a small radius, but included angle of the edge (plane 1 degrees from centerline + plane 2 degrees from centerline) is as important a factor. The size of the radius will increase with the size of the included angle. Unfortunately, the durability (how much strength or metal is behind the edge) decreases with the decrease in included angle. We are always fighting the metal to get the best balance between edge radius and durability.

Utility knives, razors, scalpel,s and anything of that ilk sacrifice durability for sharpness. Sharpen often or put in a new disposable blade. So edge angles are going to be minimal, but these things will really cut; for a while.

So what is the proper angle for a knife edge? I feel a range of 20° to 50° is about right, but covers a lot of territory. I guess some examples might be appropriate.

Bench Knife or skiver -- 20° to 25°, maybe even 30°

Shoe Utility Knife -- 25° to 30°

Pocket Knife -- 25° to 30°

Kitchen Knife -- 25° to 35°

Head Knife -- 20° to 25°

Wood Chisel -- 25° to 35° depending on use

Planer Blade -- 40°

Axe -- 40° to 50°

Lawnmower Blade -- 90° or a bit less

Art

[x101airborne]

I would like to also see something about kitchen and butcher knives. Having a dull kitchen knife is akin to a dull head knife. Useless, dangerous and frustrating. And we all need to do something with that delicious meat that used to be wrapped in the skins we use!

Since an edge is the intersection of two "planes", we could call it "The Plane Truth". LOL.

[Art]

Kitchen and butcher knives, in my experience, run the spectrum of knives, from paring knives to cleavers. Also the use that these knives get is anywhere from home kitchen to the commercial processing facility.

The average home kitchen knife can be sharpened from 15° or less, all the way up to 40°. The average chef type knife will be in the 25° to 30° range for the "gourmet home chef", although some of the Japanese blades hold 15° pretty well. Edge life varies both with use and care. If you go into the average home kitchen, they might as well be using cold chisels to cut things as the knives are usually in abysmal condition.

Commercial Kitchens are worse at times than home kitchens. For the type of work they do, they usually go an inordinate amount of time between sharpening unless they have a service. Knife sharpening services want paid before they leave and most restaurants are not the cash cows they seem to be. One of the banes to knife practice in commercial kitchens is the "abrasive steel". These little beauties are made of, or coated with, ceramic, or ghod forbid, diamond. There seems to be no way to keep these things out of the kitchen, either home or commercial, and the result by the time the sharpening service gets there is a kitchen full of, for lack a better word, butter knives.

Processing plants are a lot better. They usually run on two shifts, with a cleanup shift as the third shift. This is when the sharpening gets done by someone who knows what they are doing. These knives are in contact with bone and chainmail for two shifts and often carry a 40° included angle, some go with 35°, and will go smaller only if a knife will last through two shifts, some applications yes, some no way. The 40° angle is durable and stands up to steeling well, and steeling is an effective and common practice.

Butcher shops are semi-processing plants with butchers who maintain their own knives. Food store meat departments have some of the sharpest and dullest knives I have ever seen.

Commercial knives are the best for the home kitchen to the processing plant. They are well made. Forschner and Mundial are good brands, with Forschner superior. There is no steel like a Dexter, they don't have to sell to the home market, they do just fine in the commercial marketplace.

I could rail you with stories of the kitchen sharpening days, but it might be easier to ask questions and get some dialog going.

Art

[x101airborne]

I appreciate the response. Like you, I am a sharpening fanatic. I don't do commercial sharpening, but rather sharpening for 6 households. From lawnmower blades to pocket knives I sharpen it all and during hunting season run my own private butcher shop making everything from aged beef to deer sausage. Thusly, my knives are important tools to me and I love each and every one. Even the cheapest knives have a place in my life cutting hay string or as "loaners".

My absolute passion is my processing knives and kitchen knives. And I am always looking to pick up a new trick or skill to make them sharper and work better.

[Art]

I just looked at your profile, and if you are a knapper, you already know that knapped obsidian is about the sharpest edge you can get, but again, they don't last long, but are easy to maintain.

It takes about five years of experience to learn the sharpening business. It is fairly simple to sharpen something, depending on what you call sharp. It is something quite different to learn to sharpen something well and do it quickly. If you want to make money at it, that is a whole different can of worms. The business can be quite expensive as tool costs are high and experimentation can balloon tool costs to pretty astronomical levels. Growth costs are even more intimidating, and just wait till you hire your first employee. Been there, done that, ain't doing it anymore. I am retired, and still make the occasional knife for friends kids going into the service, and sharpen anything that makes it to my door. I still have all the gear, so why not use it.

But you don't really need all the equipment and product to sharpen something. Professionally, doing a job and making a living at it requires all that; but just sharpening merely requires a knife to sharpen and an available rock.

If someone can learn something from me, that is cool. If I can learn something, more the better.

Art

P.S. To all using this forum. A first name is helpful, or a nickname, or a last name, or even an alias, as we can answer each other or specifically direct something at each other. Just a thought.

[Oldtoolsniper]

Art,

I hope this takes off I'd like to learn more. I sharpen a lot of stuff and scissors kicked my butt. Then one day at an auction I bought a wolf twice as sharp. I'm from farming country and little itty bitty tools like that don't sell well here. They just saw it as a little underpowered grinder. That's been a learning experience in angles and edge relationship. There are way more dull scissors in use than sharp ones.

Edited January 31, 2016 by Oldtoolsniper

[JerseyFirefighter]

Since we're talking about knives, I just wanted to take a second to show off my japanese damascus steel knives I picked up last month. 15 degree bevel on a 50/50 taper. Even when I hone these I start to cringe that I dont mess up the patterning. A gyuto, petty knife, and bread knife.

[Art]

Sniper,

How about a name to go with "Beaver from Iowa" Avatar.

I know a few guys who do scissors. They go from shop to shop with a Wolf or even just a grinder with some aftermarket jig and that's all they do, run out of the back of a van usually. The Wolf works fine for most scissors, but then you get the occasional hairdresser oops, stylist from Rodeo Drive who just has to use $1000 scissors where $150 would do. The Wolf will not do these well, I have seen the results, or maybe it was the guy running it. I have found the Edge-Pro to do a good job on any of these things, even the uber expensive ones. I got my Edge-Pro back when he first marketed it and it has worked from kitchen to salon. It now stays setup for scissors. Till you get used to the way to do scissors, you will bleed over everything, those thin little cuts hurt after a while. On the really good scissors (the $100-$200 kind not the $1000, as that's just too much for anybody to pay for scissors) you can get an 80° or 90° edge sharp enough to cut skin on touch. I really didn't believe that till I did it, and I bled. I have a roll of alligator skin tape that IF I remember to put it on, helps to keep me from getting cut-up.

Art

[Art]

Since we're talking about knives, I just wanted to take a second to show off my japanese damascus steel knives I picked up last month. 15 degree bevel on a 50/50 taper. Even when I hone these I start to cringe that I dont mess up the patterning. A gyuto, petty knife, and bread knife.

Beautiful work. The question is, collect them or use them. I just love Top Chef and all the others where the "Chefs" bring in their knife rolls with about 10 knives in them. I have only seen that once in a commercial kitchen, and those knives went home that night, never to return. I have never seen a cook or chef treat a knife well enough to have that kind of fit and finish. The dishwasher, throws them in a tray and runs them through the machine. I couldn't bring something as pretty as that to work.

Art

[JerseyFirefighter]

Beautiful work. The question is, collect them or use them. I just love Top Chef and all the others where the "Chefs" bring in their knife rolls with about 10 knives in them. I have only seen that once in a commercial kitchen, and those knives went home that night, never to return. I have never seen a cook or chef treat a knife well enough to have that kind of fit and finish. The dishwasher, throws them in a tray and runs them through the machine. I couldn't bring something as pretty as that to work.

Art

They see moderate use. I cook at home and take them occasionally to the firehouse as im the chef on the shift. Since im not using them 8-12 hours I can take the time to care for them properly. After all the prep work is done the first thing I do is wash/dry them and put them back in their place. After years of having dull cheap knives I will never go back after getting edges like these.

[Oldtoolsniper]

Sniper,

How about a name to go with "Beaver from Iowa" Avatar.

I know a few guys who do scissors. They go from shop to shop with a Wolf or even just a grinder with some aftermarket jig and that's all they do, run out of the back of a van usually. The Wolf works fine for most scissors, but then you get the occasional hairdresser oops, stylist from Rodeo Drive who just has to use $1000 scissors where $150 would do. The Wolf will not do these well, I have seen the results, or maybe it was the guy running it. I have found the Edge-Pro to do a good job on any of these things, even the uber expensive ones. I got my Edge-Pro back when he first marketed it and it has worked from kitchen to salon. It now stays setup for scissors. Till you get used to the way to do scissors, you will bleed over everything, those thin little cuts hurt after a while. On the really good scissors (the $100-$200 kind not the $1000, as that's just too much for anybody to pay for scissors) you can get an 80° or 90° edge sharp enough to cut skin on touch. I really didn't believe that till I did it, and I bled. I have a roll of alligator skin tape that IF I remember to put it on, helps to keep me from getting cut-up.

Art

I'm pretty shocked that scissors could get that sharp and it's been pretty easy. Granted I just do it for my friends and family but I won't ever use dull ones again. I sharpen my utility blades before I use them so I'm a little on the odd side in that respect. I learned to sharpen because of handplanes and my enjoyment of woodworking. I just could not figure out how to make a handplanes work. There are so many of them out there so they must work or it was one huge scam pulled on everyone that bought the millions of them out there. When I learned I didn't know what sharp was, I started down the path of learning. Funny thing about learning how to sharpen is how much stuff everyone has for you to do. I've learned to say no, I don't want a second career. I just want sharp tools.

Roy

[Art]

Hi Roy,

Planes are a whole different ball of sharpening. It is really necessary to understand the geometry of the plane bed, the blade, and the cap iron to get it sharpened properly. A lot of planes really need a little back angle (on the back of the blade) to function properly. I like to get the whole plane when someone wants one sharpened, not just the blade.

Scrapers are another animal too, too many guys have planes up the wazoo but not a scraper in the house. A good scraper like a Stanley 80 (properly sharpened and hooked of course) can save a ton of planing (with risk of tearout) and sanding.

It is hard to refuse when someone brings you a sorry tool that just needs a little TLC.

Art

[MikeG]

Art,

When I first started leatherwork, I attended a class where I was totally embarrassed that my best sharpening efforts were very poor. I quickly learned that leather tools need to be surgically sharp. I now sharpen blades on glass with wet/dry paper. Once my blades are sharp, I keep them honed, and I'm one of the guys that hones my razor knifes and scalpel blades. I'm of the belief that keeping a properly sharpened blade honed/polished is all that is needed and that resharpening is almost never required unless it is damaged or nicked. I would like your take on that.

Another question -- head knives. Is there any way to set up a jig for sharpening a curved blade? I have one that has a true circular blade and have thought of drilling a hole at the radius & using a bolt to maintain a constant angle for sharpening -- I just haven't built up the courage to drill a hole in a really nice head knife. My others are not truly round or the curve is too large to do this. So what is the best way to get a perfect uniform angle?

I am looking forward to this forum!

Thanks,

Mike

[LumpenDoodle2]

My question is in the same vein. I bought a French pattern head knife last year from fleabay. It was quite 'tired and emotional' and really needed a lot of work to get it to the point of being useable.

I admit to having minimal knowledge on sharpening knives, but it is improving. My one thing though, is getting an equal sharpness over the whole of the head knife. It's at the point now where it will cut through 4mm with ease, in fact a couple of times I've thought it was making heavy weather of it, only to discover the knife cutting deaply through my mat under the the leather.

As I've said though, not all of this knife is equal in sharpness, and I just can't get the technique quite right.

[Art]

Proper honing should work to keep the edge sharp for quite a while, but eventually, and this depends on the hardness of the steel, the edge angle will tend to increase as the edge is replaced by the steel underneath. When we hone, we do remove metal and actually create a new edge, so the included angle increases unless we actually hone the whole primary bevel and move that back. Moving the primary bevel back is actually sharpening. Every blade that I do gets a new primary and secondary. On head knives, we do a flat primary only, it just works better that way as the user can find a flat primary easier than a secondary. If you ask real nice, I'll put a secondary bevel on a head knife, but I don't recommend it as it is very hard to find that secondary when hand sharpening.

Head knives can be sharpened with a jig, but I do them freehand on a 6x48 laid down flat if it is a real basket case, or on a Makita 9820 rotary flat waterstone or a diamond rotary lap.

To make a jig for head knives (which are practically round), make a base that will present the knife at the desired angle to the abrasive. Put a pin in it that a top piece will rotate upon. You can make the top piece of delrin with holes in the bottom for the approximate radius that you want. Make a cutout in the top of the delrin piece to let the handle stick out and let the knife lay flat. Countersink and glue a couple of Neodymium magnets (eBay) to hold the wings of the blade. You'll have to work it out from there.

A Pecard's or Vaseline treated strop with .5 micron green compound (we however use 3 micron diamond paste on our rotary strops, and .5 compound on our felt wheels) will keep a knife very sharp between honing sessions.

Of course, everything can be done with stone grades extra coarse to extra fine and a strop and some compound.

Art

[Art]

Doodler,

It is much easier to sharpen any curved blade on a moving stone as you can pay more attention to your angle. Another trick you learn is that the curved portion of the blade (called the belly) can be manipulated to the proper angle by raising the opposite end of the blade. The French Head Knife (we call them a linoleum knife over here) cuts mostly on the belly, so learning to sharpen that part and presenting that part to the stone at the desired angle is most important. The other important thing is to use the same angle as you go up through the grits.

Unfortunately this is all practice, but keep a felt tip or magic marker handy and mark your edges before you stone to keep a check on doing it right. Also get a 10x glass (loupe), even a cheap one will show you any inconsistencies. Buy the magic marker before the loupe.

Art

[Pablo27]

This is such a great thread, a lot of information and experience in a couple of pages. Thanks so much Art for sharing so much with us that need it. What is your opinion of Japanese Water stones? Are you supposed to use them like regular stones with a back and forth, or circular motion or just a pulling motion like a strop? Thanks again for taking the time to help us here.

Paul

[Art]

Hi Paul,

The Japanese water stones started showing up 35 or so years ago. Before that we pretty much had Arkansas and Carborundum. At first, it was mystical hype and then we figured out you really could get a better edge with them. The downside was they cost an arm and a leg (but then a good black Arkansas wasn't cheap), and they would wear quickly, often in the form of a trough in the middle of the stone. Not a problem, DMT came out with the diamond lap, and troughs were eliminated in all stones throughout the land. They work very well, and you learn to use the stone in an allover fashion to minimize the grooving, still, they must be dressed frequently. Over time, most stones will wear, it is the nature of the beast to be friable so as to expose new cutting surfaces. The water stones seem to wear faster than others. Shortly thereafter came DMT with diamond stones which are still the best in my estimation. As far as pulling, pushing, or sawing, I don't think it matters. I'm sure someone can argue to the contrary, but I just haven't seen it. We pretty much use Diamond stones for most applications, both wet and dry, power and hand. The only waterstones we use are on the Makita 9820 grinders, and the occasional use of a Silicone Carbide stone on the Makita for carbide tools. The general tool sharpening theory is that the grind marks (be they ever so miniscule) should run in the direction of cutting. The old timers (oops, I think I are one) would tell us to sharpen a tool like you use it.

There is a new stone that is gaining popularity, the Shapton Ceramic Water Stone. They are a tad expensive, but so are Diamond Stones. Use them like a Japanese water stone, but they hold up better and are supposed to make superior edges. Ok...till the next great thing comes along.

Art

[LumpenDoodle2]

Many thanks for the reply, I do like the idea of using a felt tip pen. I did once look at the blade with a 20x loupe, made the edge look like the Pyrenees.. Scary.......

[Colt W Knight]

I grew up using a double sided Norton sharpening stone with incredible success. Then my dad gave me an burned out ceramic light bulb from a huge light on a dragline. After sharpening with the Norton stone, I could polish up the edge using that light bulb like a steel and my knives became sharper than I've ever experienced. These days I have an expensive set of DMT diasharp diamond stone from extra coarse to extra fine. These are excellent sharpening devices, but the greatest advantage to me is I use them to level and dress guitar frets. They make quick work of that.

I think my greatest evolution in sharpening came when my uncle explained how the metal of the edge tip looked microscopically. Sharpening creates a super thin sliver or feather of metal at the point. Stropping keeps that feather straight and as you use the edge it begins to roll over and makes the edge dull. If you frequently dress that edge with a steel or strop, you can keep the edge sharp longer without a need to reshapen on a stone.

Ideally, you can sharpen that feather into the edge and polish it away for the most superior cutting edge.

[Colt W Knight]

On my leather working tool strops I use automotive rubbing compounds because that's what I have on hand from building guitars and finishing with lacquer.

Sharpening isn't a big deal once you get your consistency down on your technique. One wrong swipe can erase 50 good strokes.

[TinkerTailor]

The general tool sharpening theory is that the grind marks (be they ever so miniscule) should run in the direction of cutting.

Art

This is really noticeable with scissors. I took a pair of nice shears and at the proper angle, honed them so sharp that i could cut paper with one blade almost silently. I honed them parallel to the cutting edge, put them back together and they just pushed stuff out the tips. They had no bite. One sheet of paper they would cut but fabric no dice. I took them back apart and hit the edge with 600 very lightly perpendicular to the edge, passed them over a strop, and now they bite. I can cut silk to the tip, or 8 oz veg. They eat webbing for breakfast. Before i put the micro-serations in the blades, they would just push webbing out the end, regardless of how sharp they were. I think that sound of a well sharpened pair of shears is the serrations, not the keen edges.

Which brings the question, Is sharpness a measure of the microscopic width of an edge or is it a measure of whether it will cut in its intended purpose?

Arguably I made the scissors duller, but they cut better..

[Art]

Hi TT,

It is amazing what the guy who has been sharpening scissors (stylist) for years can do to a good pair of Japanese hair shears. The German scissors are starting to copy some of the attributes of the Japanese ones. Many hair shears are cut on a radius and have convex edge profiles. If you don't realize this and have a machine and the knowledge to address it, well, the tips won't meet, they will fold and/or push hair, not close properly and who knows what else. It takes over an hour to get a pair like that fixed, and it hurts to tell them their $300 baby may not be repairable.

Art

[Sonydaze]

Between leatherworking, woodworking, metalworking, household and outdoor stuff I do a fair amount of sharpening. Some days I was fantastic at sharpening...other days not so much. I finally broke down and bought a Tormek sharpener and a most of their jigs. The Tormek has a bit of a learning curve but now it is easy to quickly and consistently get the same angle and and a good edge. The stone on it can be changed from 220 grit to 1000 grit with the supplied dressing stone, then you finish up on the leather wheels with their honing compound.

By adapting the planer blade jig, I was able to hollow grind the blades on my Osborne and Heritage splitters. I bought the Osborne splitter for $80 with a really poorly ground blade in it figuring that I would buy it a new blade. I was able to save the blade with the Tormek.

Sharpening scissors, Tormek recommends not honing the the edge.

An interesting video: http://www.youtube.com/watch?v=BQI3TsjKnbU

[Art]

I use the Tormek for Knives, and lathe tools. I need it for lathe tools, because by the time I get the tool and figure out what it used to be, the Tormek is the only way to put a new bevel on the tool. The tormek book, mine is old, it is actually hardbacked, gives me a good of what the tool used to was. But then again, I have made a completely different tools than what they brought in.

For really high grade knifework, you need a belt grinder or stones, there is just no other way to get the finer grits you need.

Art