Back Bevel Question

[Bill Rhodus]

I read a post today on Chris Schwarz's blog about back beveling block planes that intrigues me. I have gotten into the habit of sharpening my old Millers Falls block by starting on a coarse stone to remove wear to the back of the iron; this tells me I need to try the back bevel on the block and will do so (will post results at a later date). In the meantime, I am purchasing a Veritas BU smoother and would like to know if any of you have experimented with back bevels on this plane. Derek, your posts on the Veritas smoother's performance as well as how to camber the iron have contributed to my decision to purchase this plane. Have you/will you post your thoughts on this?

[Maurice Ungaro]

I am by no means an expert, but it's my understanding that one of the virtues of a BU system, is that a back bevel is not used to change the cutting angle. Simply grind a new angle on the iron face itself.

[David Weaver]

You can do it on the BU planes, but there's no great reason to. They will come as flat as any iron you'll ever find, and all you have to do is keep up with removing the wear.

Clearance is 12 degrees on the LA planes, so you need to be careful, if you're going to use a back bevel, to keep it as shallow as possible, like with a half mm feeler or something as charlesworth suggests.

[Bill Rhodus]

I have read several times on the net that the BU plane irons experience wear in the back (flat side) of the iron that requires the iron to be sharpened beyond the wear when it gets dull and thus contributes to more work verses the bevel down plane. I believe this is the crux of the aforementioned Chris Schwarz article and has been my experience with my old block. My initial reaction is there may be some validity to the back bevel to accomodate wear not to change the cutting angle or flatten the iron.

[Derek Cohen]

I found Chris' article a little convoluted, but I get what he is saying. This is not new information.

In essence ...

He is extrapolating that a 5 degree backbevel on a BU plane (a block plane) is not just to reinforce the edge of the blade (which was honed at a low 20 degrees to deal with softwoods), but to prevent the incursion of a wear bevel at the rear of the blade.

Leonard Lee has written about the use of a backbevel to strength an low angle bevel on a block plane. As David (above) warns, there is a limit to the angle size of the backbevel. Leonard Lee suggests that 7 degrees is the limit for softwoods. On a 12 degree bed, a 5 degree backbevel would be at this limit.

David Charlesworth has written about the use of his Ruler Trick in this regard. The Ruler Trick has an angle of just 0.6 of a degree.

I do believe that Chris is reaching a bit further than the data suggests. If you wish to use a backbevel to protect against a wear bevel, I would suggest you first use the Ruler Trick and not a 5 degree backbevel. The former is easier to remove if you do not wish it to remain there.

Regards from Perth

Derek

[Rob Lee]

I found Chris' article a little convoluted, but I get what he is saying. This is not new information.

In essence ...

He is extrapolating that a 5 degree backbevel on a BU plane (a block plane) is not just to reinforce the edge of the blade (which was honed at a low 20 degrees to deal with softwoods), but to prevent the incursion of a wear bevel at the rear of the blade.

Leonard Lee has written about the use of a backbevel to strength an low angle bevel on a block plane. As David (above) warns, there is a limit to the angle size of the backbevel. Leonard Lee suggests that 7 degrees is the limit for softwoods. On a 12 degree bed, a 5 degree backbevel would be at this limit.

David Charlesworth has written about the use of his Ruler Trick in this regard. The Ruler Trick has an angle of just 0.6 of a degree.

I do believe that Chris is reaching a bit further than the data suggests. If you wish to use a backbevel to protect against a wear bevel, I would suggest you first use the Ruler Trick and not a 5 degree backbevel. The former is easier to remove if you do not wish it to remain there.

Regards from Perth

Derek

Excellent summary, and advice....

You *could* quit your day job..... :)

Cheers -

Rob

[David Weaver]

I have read several times on the net that the BU plane irons experience wear in the back (flat side) of the iron that requires the iron to be sharpened beyond the wear when it gets dull and thus contributes to more work verses the bevel down plane. I believe this is the crux of the aforementioned Chris Schwarz article and has been my experience with my old block. My initial reaction is there may be some validity to the back bevel to accomodate wear not to change the cutting angle or flatten the iron.


It depends on what kind of stone you're using, I guess. If you're using a slow cutting stone and using an A2 iron, then it might be tougher to remove that wear from the back of the iron on a BU plane (i.e., if you have a black arkansas or translucent arkansas that has been allowed to really settle in to fineness and not been scuffed in a while).

However, if you're using anything even like a soft binder waterstone (like a norton) or a ceramic stone, it is not that much work to remove the wear from the back of an iron on anything that hasn't been totally neglected.

Personally, the only thing I don't like about the LA planes is that you have to be much more deliberate about the camber. For a straight iron, it takes me less time to work the wear off the back of a single iron BU plane and work the bevel than it does to take a double iron plane apart, do the same, and put it back together. There is maybe a longer bit of wear on the back of an iron (that would otherwise be on the bevel of a bevel down plane), but it is not something that you have to work off in the blade length, just the depth of the wear and it's really not that deep or that hard to remove. I would never limit my clearance to 7 degrees. It's not that you can't use a plane with 7 degrees of clearance, but use one alternating on soft and hardwoods and experiment and I think you'll find that the springback of the wood is challenging function around that point, and you may end up sharpening more often because of it.

[Mike Henderson]

I've had a discussion with a very experienced woodworking teacher some time back about this. The problem with putting a very low angle on a BU plane blade, like 20* on a block plane (which gives a 32* cutting angle because of the 12* bed angle), is that the edge becomes fragile. (With a normal 25* bevel angle, the cutting angle is 37* because of the 12* bedding angle.) You want to have a low cutting angle to better cut some wood, such as end grain, but you have to maintain the strength of the edge. By putting a 5* back bevel on your block plane (for example) you increase the bevel angle to 25*, which is what most people normally put on a block plane, while maintaining the 32* cutting angle.

What you give up is clearance angle, which drops from 12* (the bed angle) to 7*. So there's a limit to how much of a back bevel you can put on the blade before it just doesn't cut (the edge will not be able to get down into the wood, especially with the spring of the wood).

Putting a back bevel on a block plane is equivalent to lowering the bed angle. The standard 12* bed angle is set not from a "best cutting" design, but from the strength of the material that holds the blade (the frog equivalent) - the back of the mouth just gets too fragile with very low bed angles. This is a "cheat" way to get a lower bed angle plane.

Mike

[Bill Rhodus]

The issue that David brings up of using a slow cutting stone was the impetus for this post. I use an oil stone to sharpen and it takes more time to sharpen the A2 verses the older carbon steel irons. I began using Charlesworth's ruler trick when I aquired a Veritas BU jointer and have been pleased with the result, however, my jointer would not be used nearly as much as a smoother and my concerns were that I would see more wear and need to do more removal of material during sharpening of the smoother iron. Doesn't sound as if it is a concern. Thanks everyone for your replies.