back beveling chisels and planes

[Vince Shriver]

I'm reading about the advantages of putting a back bevel on plane irons, whether main bevel is up or down. Has anybody used this method of sharpening, and any comment from those who have. Thanks. Vince

[David Keller NC]

It's not a bad idea for bevel-down planes, though it will increase the cutting angle and slightly increase the resistance against pushing the plane forward.

One bevel-up planes, it doesn't do anything helpful with regards to planing performance, since the angle of attack is determined by the pitch of the frog and the bevel angle on the blade. It can serve as a sharpening aid, but if the back-bevel is too wide, it's possible that will result in blade chatter, as the blade is not supported all the way out to the cutting edge.

On chisels, it's a bad idea. You need the flat back as a jig to make straight, flat paring cuts, and a back bevel will tend to force the chisel up as it penetrates farther into the wood. The result is a curved cut away from your knife line, which isn't helpful when paring flat bottoms to dovetail sockets, paring a flat tenon shoulder, etc... The exception is flat carving chisels, which are generally (though not always) double-beveled.

[Pedro Reyes]

One bevel-up planes, it doesn't do anything helpful with regards to planing performance, since the angle of attack is determined by the pitch of the frog and the bevel angle on the blade. It can serve as a sharpening aid, but if the back-bevel is too wide, it's possible that will result in blade chatter, as the blade is not supported all the way out to the cutting edge.


Actually, you can close the mouth of a bevel up plane by back beveling. Hard to explain without pictures.

I don't really advocate this practice, I have tried it and it did close the mouth. But I'm not sure the positive effects warrant it and that the bad effects are small enough to keep doing it.

/p

[Michael Faurot]

I've used it as a method of last resort a few times on bevel down blades, when I didn't have another plane that would do the job. In general I avoid doing it as I freehand sharpen, and the back bevel makes sharpening more difficult.

[Frank Drew]

On chisels, it's a bad idea. You need the flat back as a jig to make straight, flat paring cuts, and a back bevel will tend to force the chisel up as it penetrates farther into the wood. The result is a curved cut away from your knife line, which isn't helpful when paring flat bottoms to dovetail sockets, paring a flat tenon shoulder, etc... The exception is flat carving chisels, which are generally (though not always) double-beveled.

What David said.

[David Keller NC]

Pedro - Hmm, never thought about that. All of the bevel-up planes I own have adjustable mouths anyway, so closing one up's never been a problem. But that's a very interesting observation for an antique British infill miter plane with a blade that's not the original and doesn't quite fit the way it ought to, or perhaps a "strike block plane" (a wooden miter plane).

[Harry Goodwin]

Years ago we were taught that the backs of flat ground chisels and plane blades were meant to remain that way. It may be easier to sharpen the back but just use a courser stone for that first flattening and then you are back to a flat back for the aforementioned reasons. I wouldn't buy a used tool that was sharpened that way. My own two cents. Harry

[Chris Friesen]

I think chisel backs should be as flat as possible for the reasons discussed above. Plane blades are a bit more complicated.

David Charlesworth is a big fan of a tiny back bevel on plane blades. (This is known as the "ruler trick" if you want to google it.) The advantage is that you polish the back of the bevel right down to the blade edge, without having the polish the whole plane back.

Brent Beach has done a lot of research on sharpening and wear behaviour on plane irons. Based on his testing, it's quite apparent that using a plane causes a wear bevel on the back side of the plane, and if you don't use a back bevel you either 1) need to grind away more of the front of the blade to get past the back wear bevel, or 2) are not getting the blade as sharp as it could be.

It's the same idea as the "ruler trick", but taken to its extreme. Brent actually does a 3-stage bevel (with successively finer abrasive) on both front and back. The advantage of this is that the finer abrasive has less work to do when the bevel angle is increased. This speeds up the process.

It's entirely possible that for many purposes a "half-sharp" blade is perfectly acceptable. But if you really want to get a plane blade as sharp as possible, a small back bevel is probably the way to go.