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 Joel's Blog at Tools for Working Wood

In The Belly of The Bevel - Or How To Ineffectively Sharpen Anything  


When you sharpen on a stone or sandpaper the hard flat surface of the abrasive gives accuracy over forgiveness. You either are touching the edge of your tool to the abrasive or you are not. Also, as you sharpen it's pretty common to apply pressure at the very edge of the blade and your bevel will slowly acquire a very slight belly. What this means is that the next time you sharpen there is a good chance your solid contact with a stone is actually a solid contact with the tool belly, not the cutting edge. Sometimes slurry gets caught in the gap between bell and edge and you sort of polish the cutting edge, but you don't remove much material and you don't get a burr.
This issue applies no matter if you are free handing or using a jig. It's just pretty possible to find yourself spending lots of time sharpening a belly that has no effect on the cutting edge. Most annoying. If you are actually sharpening at the cutting edge, and there is no microbevel or flat to remove first you should be able to turn a wire edge in theoretically one stroke, in practice a couple more. Just polishing the edge means slurry is working but you don't have solid contact at the cutting edge.

There are three simple solutions to this when freehand sharpening (I don't know if there is a solution when using a jig other than shift the tool in the jig). The first is to hollow grind the bevel. The second is always get make sure there is pressure on the very tip of the tool as you sharpen. The third is to lift the tool slightly to ensure contact at the very tip and form a secondary bevel. In the first case, hollow grinding makes it easy to bear on the front edge but you also need a grinder (which I consider an essential shop tool). In the latter cases, over time you will form a belly on the bevel or a series of secondary bevels and each time you sharpen you need to raise the tool a little more. When it becomes hard to continue sharpening or the belly/bevels get so pronounced that the angle of cut gets too high, just go back to square one and hollow grind. Japanese tools are flat ground not hollow ground, but the softer backing material makes developing the belly harder in first place.

97% of the time when someone complains they can't sharpen and they spent hours on it, it turns out that they were sharpening the belly of the bevel and never came close to the cutting edge. This can be because they have their jig set wrong or they are applying pressure in the wrong place. Some teachers recommend embracing the belly and recommend a stroke that starts at the belly and eventually wipes out at the edge. This works but I think it's a waste of effort.

For a lesson in good technique, see my teacher Maurice Fraser explain how to do it consistently. Check out the free website and the video.

Next time I will talk about how stropping can mitigate some of the rounding belly issues.
Tags:Woodworking Tools and Techniques
Comments: 20
02/05/2013Robert Justiana 

Is it simply incorrect, or a bad idea to hollow grind Japanese Tools?

Robert J

Glad you opened this kettle of fish! No doubt a common problem.
What you didn't stress is the concept of convex bevel honing vs.honing a hollow or flat bevel. In the latter the edge is always in contact with the stone and only maintaining the angle is important. One or two strokes will sharpen the edge. The downside of this is that periodic regrinding is required. However, in the former case of a convex bevel a completely different concept is working. Here the edge is not sharpened but rather "exposed." Metal is removed from the belly of the bevel so as to work toward an edge that thus becomes sharp. Periodic regrinding is not needed. Watch Sellers sharpen. He starts always with a coarse stone and drops his angle as he pushes forward on the stone - affecting the belly of the bevel. So, in summary, convex bevel sharpening requires a completely different mind-set vs. micro bevel or flat bevel or hollow bevel sharpening.
There is a fourth way!
You hone as normal starting at 30º but dip the handle as you go, to round the bevel slightly, but under the angle, not over. You keep going until you can feel a burr across the whole width. If this doesn't come up quickly (i.e. you are sharpening the belly as in your drawing) you move to a coarser stone and remove the belly until it meets the 30º edge. Then back to finer stone as necessary.
Paul Sellers does a good video of this and see other comments in his blog.
02/05/2013Gary Sanders 
Nicely done

I hollow grind Japanese chisels but not all the way, ject to get rid of any belly. It's certainly non-traditional but it works and saves me time - so by definition it isn't wrong. If you want to be traditional don't do it.
Jacob and Marhk,
I do mention starting at the belly method and then wiping out at the edge, which is a three word summary of what Paul Sellers teaches. You lift the tool as you go to insure contact. As I said above, it works, it's easy to teach, easy to learn, nothing wrong with the method. I think maintaining a flat is less work, just requires a slightly longer first lesson and more practice. In either case at some point you end up with a very steep angle which really should be ground. And in Paul's method sharpening paring chisels to a very low angle (15-20 degrees) will quickly result in the bevel angle being higher - which defeats the purpose of the very low angle (although I don't think Paul uses long paring chisels - but I could be wrong).
Needless to say you have a method that works, my point is that a lot of people don't have a method that works, or a method that works inconsistently. The reason is they don't realize that they are polishing a belly not sharpening an edge via one method or another.
02/05/2013Bill Solberg 
To set the angle of the bevel, I bench grind firmer and caving chisels first to get the hollow bevel, then I work the hollow down to flat on a bench stone. Having the hollow helps keep the set of bevel achieved on the bench grinder without creating a belly. Joel, it isn't clear to me what your end goal is: is it a hollow belly with a forward and aft area that gets the final hone? I may have missed hour point. Sorry.
02/05/2013Paul B 
I'm a recent convert to the Sellers method and I don't think you're quite understanding what he's doing. He's taking away some of the belly on each honing session, so there's no gradual creeping of the bevel angle. As he pulls the tool towards him, he reaches the desired final bevel angle, pushing away, he's removing the bevel material. It may require a couple of extra stokes but it also means never having to go to the grinding wheel.

I like it personally, because I can FEEL when the cutting edge is starting to abrade. I'd been doing the hollow grind and eclipse guide for 10 years and find the Sellers method faster and WAY more relaxing.
I sharpen pretty much the way you do but my point is that a lot of people have trouble sharpening because they are sharpening a belly without even realizing it. I don't have an axe to grind with any method that actually works.

I might have misunderstood Paul's method, I'm certainly not suggesting that it is ineffective, I don't think not having to ever go to a grinder is a good or bad thing. I hollow grind because it's faster, the end result is hopefully the same.
02/05/2013Paul B 
Sorry, I didn't mean to take away from your main point. I just thought the couple of sentences above the last image were directed at the "Sellers" method (about embracing the belly and wiping out at the edge - being wasted effort).
Sellers' method really does work very well.
I discovered it for myself
I think it was fairly normal, before the honing jig and accessories became so popular.
The key thing is to get a full width burr without lifting the handle and steepening the bevel.
There is very little written about sharpening before 1900 compared to what is written now. Grinding tools however was a regular thing. (honing stones of the time worked far slower than a diamond stone) A lucrative part of a hardware store business was weekend grinding services when people, mostly carpenters and joiners who worked on site, brought their tools by to be ground. Honing of course, people did for themselves.

Re: convex bevel sharpening.

With all due respect, I think that you are still stuck on the idea of sharpening the edge - and thus steepening it. So, you say, "In either case at some point you end up with a very steep angle which really should be ground." In reality if you change your point of view toward removing the belly of the bevel so as to expose the edge then you will see that the angle never grows, unless you want it to. You sharpen to remove the belly not to sharpen the edge. As you remove belly behind the edge you will reach the edge and a wire will form if you go far enough - but, a sharp edge can be had with out turning a heavy wire edge as you creep up on it gradually removing belly. Of historical interest most old tools seem to have been sharpened with a convex bevel. Also, Samurai swords are sharpened this way.
If you look at the method I was taught (click the link to Maurice's lesson in the blog) you can see it is pretty easy to maintain a bevel over time. I have tools that haven't been ground for decades but get sharpened regularly. Most retain the same angle, some get steeper over time when I am sloppy. For the past few years, since Barry Iles taught me to grind, I find hollow grinding everything saves time and effort.
I don't understand how having any belly allows you to have the ridiculously low angles you find on paring chisels or carving tools used for softwood. (as I am doing more and more carving my tools are going to lower and lower angles).

In any event whatever technique you use isn't the point of debate here. There are many ways to skin a cat. Each method has pros and cons. The point of this blog is that at some point of your sharpening you are sharpening at the edge. Lots of people aren't and don't realize that's why they are having trouble sharpening. I was just hoping to point that out.

N.B There is plenty of historic documentation that suggests that hollow grinding was a common, regular activity. That many old tools have rounded bevels isn't any indication of what was considered the most efficient way of maintaining a tool. The tools that were ground regularly would have worn out years ago and not survived. If we took the condition of antique tools found in the wild as any indication how they were used when they were used regularly the only conclusion would be all tools were dull and usually a little rusty.
02/05/2013Paul B 
I'm no kind of expert (and I don't want to be a pest) but the small diameter hand grinder seems to be a modern invention for the farm workshop. The old-time style of rough grinding was probably done on a large diameter sandstone wheel that would have left a very negligible hollow grind. A cool thing about the Sellers method is that the coarse diamond plate performs the function of the large diameter grindstone, re-establishing the general bevel angle.
02/06/2013Jim Tolpin
Be curious to know just what is meant by "sharp". Our standard here is to hone the edge and check it against the end grain of a softwood such as alder. If it doesn't raise a perfect, coherent shaving from end to end, it's not considered sharp. We use freehand method on Norton water stones--microbevel on a slight hollow ground primary obtained from a friable coarse Norton wheel. Honing takes 3 strokes at the most on the 1000 stone and then 4 to 6 on the 8000. Burr removed on the 8000 using the ruler trick. The entire operation takes less than a minute, which is important because we (that usually means me!) sharpens all the planes used in the school before a new batch of students arrive (so they know where the bar is set!)
02/06/2013Dave W 
Every time someone brings up sharpening in a blog, etc. something akin to a religious argument ensues. Jim T's definition of sharp is in agreement with mine except I use a species of southern pine to test my edge. I've saved and studied the article Joel references above. I also own the video Joel references. Thanks to Maurice Fraser's instruction and a little practice on some home center chisels I am able to put a wicked edge on my tools. However, it takes me a little longer than it takes Jim :) If you are a newbie and struggle with sharpening (like me) these two resources will have you on the right path in no time. Joel - I've got a few questions re; the topic of stropping but I will hold them until reading your upcoming comments.
My definition of sharp is basically the same as Jim's and Dave's.
Paul B, both Moxon and Nicholson explicitly mention the concaveness from their grinding stone. So allthough they used larger stones, it seams to have been relevent to them.
02/23/2013john power 
I just found TFWW website and saw this thread. Here is my sharpening technique mostly adapted from James Krenov. I use a hand grinding wheel free hand this allows me to control the shape/angle of the edge. I don't change the angle for chisels or plane blades. I regrind blades infrequently, If I need to regrind and since the grinder angle stays the same I can create a precise hollow grind quickly, I do not grind out to the edge tip, instead I leave a very small unground strip and hone using stones. I do all honing freehand on stones, I use water and oil stones depending on tool and application. I hone w/the whole belly of the bevel which provides a nice ramp - thick blades help. The precision is in my hands and the feel of the blade on the stone. If I am using a coarse stone I remove the burr on the flat side with a fine stone - I am very careful to maintain the flatness on the blade back and I keep my stones very flat - as part of my sharpening set up I have a stone flattening set up as well. I can resharpen in a matter of minutes w/this process. I occasionally strop but stropping can round the bevel so I am careful to maintain consistent, flat pressure. My preferred method is to use a fine water stone, build up a slurry, allow the stone to dry and polish the blade on the dry water stone which is dead flat. This works better than leather strops.
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