1.10.2013

Convexity...Another Option

I recently got a great email from a YouTube viewer concerned about having to buy a honing/sharpening guide.  I freehand sharpen almost all of my tools once an initial bevel has been set, however, his question got me thinking about how I used to set initial bevels on hand tools before I owned a grinding wheel or a honing guide.

I used to set up an angled piece of wood next to my sharpening stone and eyeball the iron on the stone at that angle.  I had one cut at 25deg. and another at 30deg.  After a lot of practice this provided, more often than not, a nice solid bevel on which I could easily sharpen the iron every time.  The issue was that all of my edges were at slightly different angles and sometimes the different angles reacted differently in various species of wood which sometimes changed between sharpenings/honings.  In truth, this wasn't really a problem, but I knew I could make it better.  The way I looked at it was this, I could watch the game on a black and white 1954 Packard Bell tabletop TV and struggle to see the players, or, I could watch the game on a new 50" HD LCD wall mounted television and easily see the individual hairs on the players faces.  Just because the old ways work just fine, doesn't mean there's not room for improvement.

During the last year or so, I have been experimenting with a sharpening option that I originally thought was bunk.  After I tried it one time, I started singing another tune (which wasn't pleasant for anyone within earshot).  If anything, this process removes some of the inaccuracies inherent in trying to hold the iron at a perfect angle while setting the bevel, while balancing on one foot, while whistling Beethoven's Fifth.  This process is repeatable, relatively accurate, provides a strong edge, and most importantly...it's quick.  The process I am referring to has been around for an extremely long time, and upon some further research is used by some very well known woodworkers, whom in order to avoid starting any controversy shall remain nameless.  The sharpening technique I am referring to puts a convex bevel on the tool in question.  This convex bevel helps clear chips in the same way a flat bevel does, but it works like a microbevel providing an increase in edge durability (due to a higher edge angle than the primary bevel) and making honing and sharpening extremely quick.
Three Of Many, Many Bevel Types
I'll make a video demonstrating this technique, I promise, but in the interim here is a quick rundown of how it works.  After you have flattened the back of the iron sufficiently, flip it over and rest the heel of the bevel  on the front edge of the sharpening stone and draw it back while raising the handle until the bevel rests at approximately 25-30 degrees at the back of the stone.  I recommend using moderate to heavy pressure on the steel for this procedure.  Continue this process sweeping the bevel on the stone in a shallow arc until a light burr has been raised on the back of the iron.  Be very careful not to raise the handle too high, or you will  round over the nice sharp edge you are working to create.  Use this same technique up through the grits of your available stones and then hone on your favorite honing medium (leather, paper and polishing compound, honing film, etc.), being as careful as you can to maintain the same angle on the final swing of the sharpening stroke.  I really like a piece of leather charged with some polishing compound for honing with this method as it stands up to the process a little better than some of the other methods.
Side Profile Of an Iron Bevel
Being Drawn Back Across A Sharpening Stone
The beauty in this method is that in its inherent inaccuracy there is an ability to provide better consistency.  Rather than trying to hold a perfect angle through the entire process and ending up with a moderately faceted bevel, muscle memory comes into play and this process becomes easily repeatable.  I will continue to discuss this method, however controversial, in more blog entries to come because I have seen how successful this method can be, not to mention how inexpensive!








3 comments:

  1. I sharpening ever not controversial with woodworkers? I actually started thinking about the same thing over the holidays as I watched some youtube videos from a very good woodworker who shall remain nameless - however I'll give the hint that he is not American and is from the UK.

    Anyway - I have his convex method a shot on my 3/8" chisel. Looks and cuts great. I can honestly say I was surprised because I was expecting poor results given the fact that I have never, ever, freehand sharpened anything in my life (not even in video games.) I've always used a jig. But armed with a 1000 and 4000 grit waterstone, I put a crazy nice edge on my chisel. I'm going to give this a shot on all my cutting edges to see if I like it better than my previous jig driven setup which took way longer for me to setup and use. Looking forward to the video.

    Lucas

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  2. I, too, have had stunning success with this method. Scarey sharp results, no jigs. I never would have thunk it. Learned it from the UK craftsman mentioned, as well as from Barr Quartin of Barr Tools. Bought a chisel from him, and the instructions were......the convex bevel method!? I was puzzled. Received the chisel sharpened by Barr himself, and it was soooo sharp, I had to write him and ask him how he did it. He replied, just like in the instructions!

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  3. Yep this is definitely more a creature than an item. Mine has been sent now.
    www.printman.co.in

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