Sharpening 101 part 2

[Romey]

Sharpening 101 part 2

The last article we talked about the type of edges and their intended uses, in this one I hope to explore a few ways to sharpen a blade. There is many ways to skin a cat and same applies here. There is no one way to get a sharp blade so Ill explain some of the ways I do it and have done it in the past and why I don’t anymore. Remember just because you might not do it this way doesn’t mean I think it’s wrong.

Firsts let’s look at what is sharp and when is it sharp enough. As a custom knifemaker I try to fill the needs of the customer and the intended purpose of the knife was made for. A chopping style knife like a camp knife doesn’t need to be as sharp and as honed nor would it be good for it to be as sharp as a chef knife. Wood and rope cutting takes a different edge as slicing a tomato and if you read the first article you should have somewhat of a idea the type of edge needed for specific tasks. As with each style of blade and blade edge are made for different purposes, so does each need sharpened slightly different. I prefer a more aggressive toothier edge for general purpose knives, much of what I may refer to is really only noticed by sight under a microscope and by feel in use so some imagination here is needed or if you really want to explore it, find a 10$ 100x battery operated microscope at radio shack and have a look see for yourself at the edge of various blade edges, dull to sharp.

To me a knife is sharp when it easily cuts what its intended to cut and that IS sharp enough, often times going past that is just spinning your wheels or for parlor tricks. I once made a knife so sharp on purpose that simply slapping the face of a piece of paper left a slice in middle of the paper, and then a rolled a single newspaper sheet into a tube being careful to not double it up, stood it on end and cut in a single swing into and left the bottom half on the table. Impressive? You bet, scary sharp, and a hell of a impressive trick but it wouldn’t hold that edge for very long using it for much else then paper or vegetables. But I had made that knife just for that purpose, why I bet you ask? Simply to see if I could make a knife do it. So the result is if it’s sharp enough to do the job it’s intended for and do it easily without a lot of force or pressure (think safety here) then its sharp.

The old stand by of testing for sharpness is shaving hair, Ill tell you right off that that is more parlor trick then indication of sharpness. A dull or rolled edge will still shave hair but lay into something like leather and one sometimes quickly notice it doesn’t easily slice the leather and sometimes gets worse as you go. Not to say I haven’t or don’t shave my arm hair, there is constant patch of hair missing on my left arm, this may seem contradictory to my previous statement but I do it more to feel how much pressure it takes to shave hair, very light pressure tells me I’m getting close to where I want to be to BEGIN the sharpening process but use caution. I know of one instance at a knife show where someone picked up a knife off a table to “test for sharpness†and not knowing how sharp the maker’s knives were he filleted 3 inches of skin off and was taken to the hospital. Most often I like to test the edge on what its use is for be it leather or what have you. Paper is another indicator, slicing paper especially thinner paper like a newspaper or even tougher cigarette paper is a good indicator as a dull blade will want to fold it over rather then slice it and if you have to slice very close to where your holding the paper to get it to slice means its still not as sharp as it could be.

Another thing I look at for sharpness is sighting down the edge of the blade edge up and look for glint of light reflecting right of the very edge, this shows sign of a rolled or flattened edge. It’ll take some practice to see but once you do you’ll know it right away. Just sight down the edge with some light above and to one side a bit or another, sunlight works best I have found.

Now that we have touched on that lets take a look at the edge angle, this is almost as critical as the heat treat of the steel, which is the soul of a blade. Most is not all blade edges are from 15 to 25 degree of angle relative to the spine. 22 is what most factory knives come in, and most come dull, not just dull but very dull, fact is I haven’t seen a single factory blade of any type, knives, razors, axes, chisels or leather tools that I felt didn’t need sharpened to some degree or another. The reason they come like this is, one the factory assumes you know this already or two that if you don’t know this, then a super sharp blade shouldn’t be in your hands to begin with. Here is a list of the degree and intended uses.

15 to 17 degree is where your fillet and kitchen knives as well as lot of razors are angled at. Very scary sharp but at a price, not a lot of steel behind the edge to keep it sharp with hard use also generally easy to hone back or simply use a steel to straighten the edge back and its ready to go again.

17 to 20 degree is where you’ll find the best all around edge for cutting and slicing. I find 19 to be the optimum area for my knives but it requires very good steel and a high performance heat treat for edge holding ability.

20 to 25 degree is where most factory blades are set, they will get sharp, sometimes it takes some work to get then real sharp but tend to hold the edge well once one is, as there is a lot of steel behind the edge. Also a less controlled heat teat of the steel (mass produced) can be gotten away with at this angle. Anything above this is into cleaver, axe hatchet area depending on the type of grind as discussed in previous article. Probably most head knives as well which id like to discuss at some point fall in the 20 degree and up area.

A good trick to figuring and keeping the angle when hand honing is using coins, stacking coins on your stone and laying the spine on the edge of the coins. For instance on a knife if you have a knife blade that’s 1.25 inches wide and .25 thick at the thickest part of the spine then the gap from stone to bottom of spine should be 0.282 inches which can be converted to 3 dimes and 2 pennies stacked up. A head knife would be a big different to the radius of the edge but a rough starting point for the front of the head knife could be if 3 inched wide and .25 thick with say 21 degree would come out to 0.95 of a gap or 6 quarters and 7 nickels. If anyone wants to try this and wants the coin stack figured just let me know id be glad to do it. In the next part we will get to the actual sharpening techniques I use and know about as well as some of the tools and gadgets will be discussed. Feed back and comments appreciated.

Until then keep a light rein, a foot on each side and a far away look

[bruce johnson]

Romey,

Thanks for that installment of the sharpening tutorial, and I am looking forward to the next. I had a round knife with a lot of drag. It was a pretty thick blade, and the bevel seemed a little steep. I took this knife to the other extreme and really thinned about 1-1/2 inches of blade. I was smarter than a tree full of owls for a second, the knife cut really well for about a good 2 feet, then drug worse. Strop and good for another two feet. I am sure you can guess that the bevel was too flat and no metal behind the edge. It would roll very easily. I was able to salvage this knife by taking the edge back to more meat, and then putting a steeper "secondary" bevel on the blade. It has been my favorite knife for the last couple years now. Do you have any thoughts on putting a steeper short bevel on a thinner blade?

Bruce Johnson

Edited May 10, 2007 by bruce johnson

[Romey]

Bruce,

You’re very welcome I hope the articles help. Sounds to me like you found by your own experience exactly what I been referring to in the article. That drag is the exact thing one can only feel to understand, too much meat behind the edge will cause drag as in such as a convex edge, to little and there isn’t enough meat to suppose the edge. It’s the very reason why 98% of the blades I make are flat ground blades with a flat ground secondary edge at 19 degrees. I have seen some head knives flat ground with a convex edge which makes sense because it gives a person the most meat behind the edge with the least amount of drag in deeper leathers, the problem is you lose some ability of fine cuts with a convex be it on the edge or the whole blade.

As for your question you pretty much summed in up with what you actually did on your blade, It would be best for heavier cutting with a thin blade to have a slightly steeper secondary bevel IF your purpose is tougher cutting like leather. The thinner the body of the blade (main bevels) the more you can get away with steeper secondary bevels. When one gets right down to it, an edge could get down to a single molecule wide and they are getting close to it with diamond chips in scalpels. But breathe wrong on it at till dull or break.

Also if your resetting a grind yourself, although I doubt this is the case with a head knife , sometimes a person can grind so far up towards the spine you run yourself out of the Martinsite which is what has make your steel hardened and you can end up sharpening softer and softer steel as one goes. I have seen this in edge quenched custom blades where only the edge was hardened. If your ever curious, run a file down the edge, it should slide pretty easily without digging in to much if at all. If the file bites in ALOT, there is likely a poor heat-treat issue as hand.

Edited May 11, 2007 by Romey

[Romey]

Bruce I have a question for you and anyone else who cares to comment. You said that head knife was thicker then normal before you reshaped it. Would you happen to have a guess as to how thick it was, how thick it is now?

A saddlemaker friend of mine asked me to make him a small headknife identical to one he had already but smaller. I studied the one he had, it had no secondary edge, a full convex zero grind almost a flat grind with a very slight convexing but it was very thin like 1/8 at thickest. Is that about the norm for thickness across the board for headknives? That headknife was a Osborne by the way.

I am trying to see if there is anything besides heattreat and choice of steel that I could possibly improve on and your insight would be most appreciated if you have any ideas. In theory that grind i described on his osbourne would be ideal at that thickness but it would be Im going to try a thicker flat grind with flat ground secondary edges. Ofcourse he wont beable to sharpen it like he does the other (felt wheels)

[bruce johnson]

Romey,

This knife (and I have another) is a Clyde. I also have an Osborne to compare to. The Clydes feel just a tad thicker at the back edge than the Osborne. I have no micrometer, but butting the back edges against each other, the Clydes are a little higher, but not a bunch. I am not good on angles, but the Clydes when I got them had about 1/2" of bevel. I took one back to about 1-1/2" of flat bevel on both sides. Wet/dry on the stamping granite. Then I took the outer about 1/2" even thinner by flattening the angle more. (At this point I am thinking like my surgical instruments - flatter angle, less tissue drag)That left a little ridge where the two angles met. I polished that off with a swatch of wet/dry on my finger to ease the ridge. Polished everything up on the strop and went to town for 2 feet, strop and two more feet. I could feel the edge curling. I took the edge off square until I had a definite visible even flat edge, and then sharpened that at a higher angle to make the steeper secondary bevel. Seems to be working, I usually only have to touch up on the 1200 to 4000 wetdry, and then strop lightly if I really abuse the blade. If I strop more regularly, that is about all I really have to do though.

Bruce Johnson

[Romey]

One thing I wonder about is, I wonder what folks use for a cutting table, I have seen marble used to cut on and that alone is going to dull even the toughest steel. My saddlemaker friend uses a large sorta plastic half inch sheet to cut on. When I picked up my stamping marble at the Monument maker place they had these real nice thick sorta plastic boards about a inch thick they lay the marble on when doing whatever they do on it, they regularly throw them away and said I could have any they had outback in trash, there was about 50 of them so i nabbed one up,wish id have grabbed all of them now, works better then anything else i have found as of yet altho most everything I do is with a clicker knife and not a head knife. Got the whole works for free,marble and all.

I bought a couple new sharpening systems to help with the next article as im going to touch on a few products one was OK and another was ACK for 30$ I exspected much better quality. Most people arent going to beable to sharpen as I do starting with a variable speed belt grinder so i figured Id do some recon on other hand sharpening stsyems out there, Hopefully they will take the one back its that bad I dont even want to waste space with it.

I decided im going to try and make 2 headknives, One a flat ground with flat secondary edge and the other a slightly convexing zero grind , same heat treat same steel same thickness and see what works best. Grinding them on a 2 inch wide belt is going to be as much of a challange as forging them from one inch round bar, headknives are odd shapes to forge. I suspect they are stamped out or laser cut out and then machine ground so the thermocycling in the forge alone should be a huge improvement. And without question a more personal higher standard of heattreating will be a bonus and before anyone asks I dont plan on making them to sell in quanity, they are gunna be a pain I suspect.

[Killerkaney]

This article is really interesting is there any update ? Have you considered a sharpening for dummies?

K

[prc77ro]

If people are still having problems maintaining an edge on their round or head knives try sharpening at a MAX of 20 degrees then increasing to a MAX of 30 degrees, should put a razor edge on. The old addage of " do the same amount of passes on each side" is incorrect. You should be sharpening on one side untill you feel a burr on the opposite side which means you have reached the center point. Then continue the same way untill you get a burr on the opposite side. The burr should be the entire length of the blade. once you have finished that with whatever your choices in grit is then strop and your ready to go. A good reference is The Razors Edge.

Also I think all the terminology is, well, incorrect or maybe generic slang is more appropriate. The blade grind is the portion that looks like it was done with a large grinder, the length of the grind shows the diameter of the wheel. The Relief Edge would be the first angle or "bevel" as stated above with a MAX of 20 degrees. and the Edge Angle is the actual cutting edge with a MAX of 30 deg. All in all the Grind determines how much of the knife blade can be sharpened before it must be reground. A Flat Grind woud have to be reground more frequently as sharpening would cause the blade to thicken quicker. Oh one more thing arent Convex grinds found more on axes?