Builders' Forum Archives
Re: Block Plane
Posted by Mark Camp on Oct 11, 2004
Good observation about the real cutting angle of a block plane. Never thought of that!
Now that you mention it, the real REAL cutting angle might even be greater than 21 + 25. Block plane irons are often honed to 30 degress. The way I figure it (now), the hone angle, not the sharpening angle, determines the angle of cut, for "upside down" irons like block plane irons.
You are so right about sharpening till the flat side is perfect. Applies to other planes as well. It's not sharp until it passes the "glisten" test.
Hold the iron up to a light, with fairly dark background beyond. The flat side is up, and the cutting edge is away from you and closer to the light. Now slowly rotate the iron back, so the cutting edge is rising and you are seeing the flat back at less and less of an angle. At a certain point, you will suddenly see the light reflecting off the back of the iron. As you continue past this point, the flat side turns dark again, and one of two things will happen, depending on whether the iron is sharp and ready to be honed or not.
(a) DULL: You will see an infinitesmally thin, irregular "glisten" on the edge. If the iron is quite dull, you will see it all along the edge. If it is nearly sharp but the stone or sandpaper has not yet reached the most worn part, the glisten will be only in the middle.
(b) SHARP: The edge will be dark. No light at all, not even tiny little "dots" of light. Dots would be tiny chips, which means you still have to remove more metal from the other side.
You can use the same test for honing. Now the unfinished (sharpened) parts of the edge will be shiny, but the finished (honed) parts will reflect like a mirror.
In Response to: Re: Block Plane by Dave Houser on Oct 10, 2004