Radius Grind on Plane Blades

[Mark A Johnson]

After about 10 years I'm switching over from using hand stones, to the Jet 10" wet sharpener. I have server nerve damage and I just can't spend the time sharpening any more. My question is with the wheel sharpeners they create a radius on the blade. Opposed to the flat face you get from hand sharpening. Does the material removed in that radius create a weakness in blades?

[Lee Schierer]

Theoretically yes, practically no. The amount of material missing due to the radius is very small and with hand plane pressure shouldn't make any difference.

[David Kuzdrall]

I think you may be referring to a hollow grind as pictured below:

As previously mentioned, if it does technically weaken the blade it won't be enough to have any impact.

[Aleks Hunter]

I use a 10" wet grinder as well. Hollow grinding doesn't make you have to sharpen the blades any more, and as long as you metal detect you're pretty safe from nicks. Knots in very hard woods of course negate this.
One thing I have found is that putting a small 10 degree back bevel on the blade makes a huge difference. Not a big bevel, about 1/32, just enough that you can see it. IT wont be any smoother on straight grain with the right tearout but you will have a LOT less tear out any place the grain gets figured.

[Mark A Johnson]

Sorry I picked the wrong name. It took me a bit research to find some pieces on using the back bevel. Reading some of the knife forums, about the different micro angles they use to per mote blades holding their sharpness. Anyone try a similar approach to the different blades we use?

[Lee Schierer]

Check with the folks over on the Neander forum, they can give you lots of good advice on sharpening and adjusting hand tools.

[Andrew Pitonyak]

Does the material removed in that radius create a weakness in blades?

Probably need an engineering analysis on this to know for certain, but, it is not something I remember anyone discussing previously. There has always been more concern as to the angle of the grind because the failure point is usually related to chipping at the edge. If you have a 10" wheel, how deep is the hollow grind at the deepest point? I did a quick calculation, and if the length of your bevel is between 1/4" and 1/3" the depth is in the neighborhood of a few thousandths of an inch.

I won't bother with a picture, but, the math is something like r - sqrt(r*r - x*x/4) where r is the radius of the wheel (5 inches) and x is the length of the bevel. So, if it is 1/4", you have about 0.002" and for 1/3", about 0.003"

[lowell holmes]

I've used hollow grind sharpening in the past on chisels. They were incredibly sharp.

I use diamond hones now, but if the occasion arose, I would not hesitate to sharpen chisels on a wheel.

I probably would not put my Lie Nielsen chisels on it though.

I used to have a trim carpenter working for me that sharpened his chisels on a belt sander.

I have put a particularily beat up plane iron on the belt sander with a LV sharpening jig. It set the primary bevel exactly square and straight.

[David Weaver]

Sorry I picked the wrong name. It took me a bit research to find some pieces on using the back bevel. Reading some of the knife forums, about the different micro angles they use to per mote blades holding their sharpness. Anyone try a similar approach to the different blades we use?

I think now you're leaning toward double bevels. We don't generally make an appreciable double bevel on plane irons because it makes the plane significantly harder to push. If your question is whether or not it's a remedy for material removed in a hollow, the answer is not really, especially not if you're using something with a very wide radius like a wet sharpener.

[Andrew Pitonyak]

I probably would not put my Lie Nielsen chisels on it though.

I have only ever seen or touched one Lie Nielsen chisel (about one week ago). It was very much not sharp. The back was flat, so it was flattened very quickly, and after putting it on my Tormek briefly, it was very sharp.

[lowell holmes]

And I have never touched a Tormek.

They must be a joy to use. I would not hesitate to hollow grind any edged tool on a Tormek.

[Mark A Johnson]

I hadn't though about back bevels and multiple angle until I did some research after Aleks bought up the issue. I figured I owed it to the board to understand what was being presented. I'm more into keeping it simple. A basic angle with a micro angle as I have done in the past is fine with me. Going to a power sharpener is more about saving myself time, along with reducing the physical pain. Allowing me more time to actually work on wood. I grew up using oil stone to sharpen knifes and spent many hours making things scary sharp.

Reading the posts has bought up an issue I hadn't considered. With the exception of 1 Veritas BU low angle plane, the rest of my planes are all LN. Would you have any issue sharpening your LN plane to a hollow ground blade? 2nd: How many times can you hone a blade before you need to regrind the bevel?

[Mark A Johnson]

Interesting, seems back bevels idea is making the rounds

http://www.toolsfromjapan.com/wordpress/?p=1007

[Chris Hachet]

And I have never touched a Tormek.

They must be a joy to use. I would not hesitate to hollow grind any edged tool on a Tormek.

As the owner of the above mentioned chisel, I can attest to what a nice job the Tormek did!

[Jeff Duncan]

I've always done hollow grinds on blades, it's how I learned in shop class and it works for me. In reality the hollow grind will make your life easier as there's less work honing the chisel/iron after grinding since you've much less material to remove. Your basically just hitting the two edges of the hollow vs the whole tip....if that makes sense? Anyway I do everything this way, chisels, plane irons, regardless of brand. I have Stanleys, Records, Lie Nielsen, Henry Taylor as well as a bunch of misc. mixed in and they all sharpen pretty much the same to me.

good luck,
JeffD