3 deg micro bevel on opposite side of blade?

[Will Blick]

I was reading this great web site by Brent Beach on sharpening

http://www3.telus.net/BrentBeach/Sharpen/bevels.html


he suggests a 3 deg. micro-bevel on the back side of plane blades. After reading the web link and looking at the graphics, it seemed this is a GREAT idea. With a flat back, when a knick occurs, you must remove a lot of the front micro-bevel to remove the entire knick, eating a lot of material and taking a lot of time. Brent mentions a symptom of this, which is when you start with a new plane blade, which cuts ultra sharp, then re-honing never quite gets you back to that new like condition. I must admit, I have experienced this.

With the 3 deg micro-bevel on the back side, the knick at the edge, now becomes easy to remove, and will re store a perfectly sharp edge in very little time. He mentions the back bevel method will allow you to re-hone by using 10x less material to restore the edge, saving time, the blade, and your stones! The concept seemed so obvious, I am surprised its not utilized more often. I remember Derek mentioning this on his web site also.


How many of you back bevel you plane blades? How do you get that back bevel on the blade? (probably the trickiest part of the process, so as re-honing does not become cumbersome) Brent offers some great suggestions for this....

Thoughts?

[Jim Koepke]

How many of you back bevel you plane blades? How do you get that back bevel on the blade? (probably the trickiest part of the process, so as re-honing does not become cumbersome) Brent offers some great suggestions for this....

Thoughts?

I have not done this. Have read of doing it to raise the effective angle of the blade. A 5° back bevel will make a 45° frog act like a 50° frog.

Have also read here at SMC of using a thin metal ruler to "lift" the blade to do this.

jim

[Joel Goodman]

I think there is also a theory that a bevel up plane tends to suffer from this "wear bevel" on the flat (non beveled) side of the iron and that normal sharpening doesn't always take it off. So the back micro bevel would cure that.

I haven't tried it or the ruler trick as it seemed easier to just flatten the iron once properly -- but maybe it's got other advantages.

In a bevel down plane as Jim points out the micro bevel increases the attack angle of the blade -- but doesn't it also open the mouth?

Good topic -- would like to hear from back bevelers -- for both BU and BD planes.

[Will Blick]

agreed as a means to change angle for BD. But the purpose for BU is not to change angle, (although it will, which if you really wanted to, you could re hone the front bevel accordingly), but instead, to create an ultra sharp edge, and re-establish it very quickly....

Brent also points out, that about 100 - 150 strokes of a plane will push the edge into the re-hone stage......very interesting..... of course it will obviously still cut, but his point was, at this stroke count, you would feel the benefits if you re-hone....

[Clint Jones]

I use the ruler trick to back bevel plane irons. I dont know the exact angle it creates but I assume its less than 5 deg. This is time saving when you have alot of irons to sharpen also when a blade is heavily pitted this is more effective than polishing the whole back.

[ken seale]

I do what Clint does for exactly the same reason

[Johnny Kleso]

Anyone wanting to figure how many degrees here is a way using the ruler trick..

1* = .017 at 1"

That means if you have a .017 thick ruler 1" from the cutting edge you have a 1* angle..

At 2" you need .035 (thick ruler) and 3" away .051

To get a 3* at 2 1/2" your ruler needs to be .128 (1/8") thick which is a combination square size ruler..

5* you want a 1/4" and you get 6* so increase the distance from 2 1/2" to 2 3/4" or so to get 5*..

[Mark Koury]

The ruler trick is from David Charlesworth. It is a reliable way to get a back bevel - if you can keep the ruler stuck to the water stone. I end up using one hand to hold the blade and one to hold the ruler, not my usual way of holding the blade - but it does work and it is repeatable.

[gary Zimmel]

I also use the ruler trick for all of my plane irons.

Picked it up from a course by Rob C. He told us he got it
from David C.

[Joel Goodman]

Has anyone found that they needed this for a BU plane? I know the theory but in practice is it needed or helpful? All my plane irons have flat backs-- seems sinful muck with them! Would love to hear Derek's take as he's been a BU fan and is working in some tough woods.

[Chris Friesen]

Has anyone found that they needed this for a BU plane? I know the theory but in practice is it needed or helpful? All my plane irons have flat backs-- seems sinful muck with them!

The issue with BU blades is that any back bevel reduces the clearance angle, so you'd want to make it fairly shallow. However, the shallower you go, the more material needs to get removed to get the same effect at the cutting edge.

Also, while the plane irons start out with flat backs, it is apparent from Brent's photomicrographs that they do wear on the backs, so right up at the cutting edge they aren't actually flat anymore after some use.

[John Schreiber]

I was reading this great web site by Brent Beach on sharpening . . .

As I read this, I saw the logic of Brent Beach's argument, and thought that perhaps I need to change my sharpening system.

Then I remembered that I am quite impressed with the present sharpness of my tools and I decided to chill and not worry so much.

My take away from what he is saying is:

1. Your edge is going to microscopically dull immediately after you start using it.
2. That means the exact shape you hone to is not that important.
3. You could save some work by honing your blade to a shape which is similar to shape of a very slightly dull blade.
4. While you would save some work, sharpening would be more complex.

I'm glad people like him are looking closely at the sharp end of their blades, but I don't see that he has learned anything that is significantly different from what craftsmen have learned over the years.

[Chris Friesen]

My take away from what he is saying is:

1. Your edge is going to microscopically dull immediately after you start using it.
2. That means the exact shape you hone to is not that important.
3. You could save some work by honing your blade to a shape which is similar to shape of a very slightly dull blade.
4. While you would save some work, sharpening would be more complex.

My take on what he is saying is this:

1) A sharp edge requires the intersection of two planes.
2) With use you will get a wear bevel on the back side of a plane blade.
3) Because of 2, in order to get 1 you need to either a) hone a back-bevel, b) re-flatten the entire back to remove the wear bevel, or c) grind away the primary bevel on the face far enough that you grind through the whole wear bevel.

Obviously options b and c are not viable, so either you hone a back bevel or else you leave the wear bevel as-is. If you don't hone the back bevel, then no matter how finely you hone the bevel, the back side will be the wear bevel (and thus rough at the microscopic level) and so the edge won't be as sharp as it could be.

[Will Blick]

Chris, very well said..... the more you look at his graphic, the more compelled one is to create that small back bevel. I thought it was ironic when he mentioned the consequences of creating wear on the back.... i.e. when you get a new plane blade it cuts ultra sharp, but yet after several re honings, it never seems as sharp vs. its first use... and I have experienced this a lot of times... as I was not hoggin enough off the flat back to remove the wear marks... I used to think just a shiny flat back was all that is required.... it seems so obvious to me now, I wonder how I did not think of this. But, it does require more work to hone now....

An interesting set-up would be... use a standard honing jig for the primary bevel. For the rear bevel, attach a 2nd honing jig....but it must roll on a surface below the top of the stone, to achieve a 3 deg bevel. Assuming something like this worked, it would sure speed up the re-honing of a dual angled blade.


> any back bevel reduces the clearance angle


Can you explain this clearance angle? I assume you mean the cutting angle?

[Joel Goodman]

Clearance angle is the angle between the bottom of the plane iron and the work. In a BU low angle it is 12 degrees. A back bevel reduces this. At some point it would become too low for the plane to work correctly. In a BD it is typically 45 degrees minus the bevel of the iron say 25 or 30 degrees for a clearance angle of 15 or 20 degrees. So it's a BU issue for back bevels if they get too big.