Archive for ◊ July, 2019 ◊

Author:
• Wednesday, July 31st, 2019
bevel-up planes

A few more points on this topic:

1. If you had a BU jack plane with a 20° bed, could you still use it on end grain? Sure. My Lie-Nielsen #9 “iron miter plane” has a bed of 20° and it works wonderfully on end grain, and so does my L-N shoulder plane with a bed of 18°. Perhaps this is so because resistance is indeed determined solely by the attack angle and not by the sharpening angle per se. 

2. This is not about block planes, which, of course, also happen to be bevel-up. It is about BU smoothing planes and, to a lesser extent BU jack planes. Incidentally, I suspect one reason for the popularity of 12°-bed block planes over 20°-bed models is that the former are more compact and thus easier to manipulate with one hand. 

3. This is not just a theoretical discussion. BU planes with 20-22° beds have been designed and are available from distinguished planemakers. Take a look at Karl Holtey’s #98 Smoother. Philip Marcou offers bevel-up smoothing and jack planes with 15° and 20° bed angles. [Drool, drool . . .] Though not it’s intended to be used as a smoothing plane, I’ve experimented with setting up my L-N #9 (20° bed) as a high-attack smoother. It works. 

So, what’s the point of these four posts? It is simply this: a good addition to the Lee Valley and Lie-Nielsen product lines would be, at the least, the option of a bevel-up smoothing plane with a 20-22° bed. (22° would suit me just fine.)

Author:
• Tuesday, July 30th, 2019
bevel-up smoothing plane

To create higher attack angles, such as 55°, to reduce tearout with a bevel-up smoothing plane, here are more advantages to a 20-22° bed angle versus the commonly produced 12° bed angle. 

1. A higher bed angle requires less camber in the edge to achieve a given “functional camber.” Please see my post that defines the terms I am using and explains the simple math, and this post that shows the effect of bed angle. A blade placed in a 12° bed requires about 75% more “observed camber” to achieve the same functional camber as when placed in a 22° bed. For example: you must grind .014″ camber to achieve .003″ functional camber in a 12° bed, but only have to grind .008″ to achieve the same .003″ functional camber in a 22° bed. 

Putting camber in the blade edge takes time and it’s easier to do if there’s less of it.

2. As the wear bevel develops on the lower (flat) side of the blade, an adequate clearance angle is maintained longer when the bed angle is greater. Again, I reference Terry Gordon’s article in Furniture and Cabinetmaking magazine (November 2018, Issue 276, pp. 48-50) and Brent Beach’s website.

Here are two more possible advantages to a 20-22° bed versus a 12° bed, but these are speculative.

1. For a given attack angle, the narrower sharpening angle (as would be used with the higher bed angle) may produce less resistance in the cut. I’m not sure. Maybe resistance is instead determined only by the attack angle, as has been suggested to me by a planemaker. I do not have a way in my shop of making an apples-to-apples comparison. I’d need two planes, identical except for bed angle, then make the same attack angle in each – for example, one with a 22° bed and a 33° blade (=55°) and the other with a 12° bed and a 43° blade (=55°).  

2. Perhaps the steeper 20-22° bed is an advantage in design and manufacturing in that it is sturdier and less likely than a 12° bed to deflect downward. I don’t make planes, so I don’t know.

Coming up: just a few more points.

Author:
• Monday, July 22nd, 2019
bevel-up plane blades

In the previous post, I discussed how a 20-22° bed in a bevel-up smoothing plane can produce a wider range of useful attack angles without resorting to excessively high sharpening angles. The use of narrower sharpening angles has, in turn, several advantages:

1. Sharpening is easier. It is simply more difficult to get a good, sharp edge at, for example, 43° than 33°. It is also awkward to work at the higher angles, and the feedback from the surface of the stone is not as good. I think this is readily evident but some may disagree.  

2. Based on my experience, and I think most woodworkers would agree, a blade with a very steep secondary bevel dulls faster than one with a more usual, narrower bevel, all else being equal. 

—————————–

Sidebar: how an edge dulls

The profile of the sharp edge of the blade ideally starts out as two straight surfaces meeting at a clean, sharp point. As the edge wears, steel is abraded away from the surfaces near the edge, and the original point becomes rounded over. The worn surfaces of the blade that approach the blunted edge can be thought of as “wear bevels.” Thanks to Brent Beach and Steve Elliot for their development and detailed study of these concepts.

For both bevel-up and bevel-down planes, the wear bevel on the top side of the blade (the side facing away from the wood) is wider than that on the bottom side, because it is the top (front) of the blade that bears the brunt of the collision with the wood. The bottom-side wear bevel, which is on the flat side of the blade in a BU plane, is nonetheless important.

Brent Beach explains the value of removing the lower wear bevel when sharpening to regain a truly sharp edge, to maintain proper clearance of the blade edge from the wood, and to avoid the need to apply undue pressure when planing. David Charlesworth’s Ruler Trick is thus particularly helpful for bevel-up plane blades.

——————————-

3. A functionally sharp edge is preserved longer when the blade is sharpened at a narrower angle. This is consistent with point #2. Australian planemaker Terry Gordon explains this nicely in a recent article in Furniture and Cabinetmaking magazine (November 2018, Issue 276, pp. 48-50). It is best understood diagrammatically but the gist is that a skinnier edge retains useful sharpness longer by remaining narrow longer.

In summary, there are important advantages in sharpening and edge endurance when using the narrower sharpening angles permitted by a higher bed angle in bevel-up smoothing planes.

For example, if you want a 55° attack in your BU smoother, you’re better off being able to sharpen at 33° with a 22° bed (=55°) than having to sharpen at 43° with the 12° bed (=55°) in currently offered stock planes.

Coming up: still more issues. Can you tell that I’m building a case that I think L-N and L-V should hear?