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From a Presentation by Mark Bolinger (Woodworkers Club of Houston) at the August 2015 meeting.
WWCH’s own Mark Bolinger spoke to club members and guests about sharpening at the August 2015 meeting. Although his talk addressed mostly hand planes the principles apply to similar instruments such as chisels. Using a folded magazine insert reply card, Mark pointed out that the objective of sharpening is get two planes (in the geometry sense) to meet in a perfect straight line.
Mark reminded everyone that you don’t have to dread sharpening, but you do have to sharpen frequently to keep them sharp because sharpening is 75 % of success with using hand planes.
Mark addressed two strategies for sharpening: hollow ground or secondary (micro) bevel. Hollow grinding leaves you with only a little bit of metal to remove for the final bevel.
Hollow grinding requires the use of a grinding wheel – the curvature of the wheel will create the hollow space. However with this technique you must not overheat the blade lest you lose temper – the blade, that is, and maybe yours too. The advantage of the hollow grind method is that you can do the honing by hand, since the bevel will now register on the stones with no variation in angle; it solidly rests on the two ends of the arc created by the hollow grind.
To determine the angle of the edge you need to know if your hand plane is bevel down or bevel up. If one is unsure, it should be easy to determine with a quick internet search for the model of the plane. The following reference is an excellent discussion of the angles involved http://www.amgron.clara.net/page73.html.
For bevel up plane blades Mark recommends the micro bevel method because putting in the hollow grind affects the angle required.
To begin sharpening you need to flatten the back first. Mark states that there is no way around this.
After the grinding is complete you begin the honing. With stone grits Mark starts out with grits of 800, then successively 1200, 6000, then finishing up with 12000. It's ok to stop at 6000 or 8000 grit, Mark only recently acquired the 12000 grit stone.
Stropping is the final step. Mark points out that the literature has many ways to do it and it is hard to find a good explanation as to what stropping is and why it works. The best explanation that Mark found is that the strop is a little bit flexible whereas everything else is rigid. This flexibility cleans off imperfections.
To re-sharpen an edge with a microbevel, or to return to the original angle, you will need to use a guide. Mark showed some examples of clamp on top and clamp on the side jigs. Mark stressed that you needn’t worry about being in the exact position you were before because you can’t go back and repeat perfectly that secondary bevel. In effect, you need to recreate the secondary bevel. It's easy to do unless you over sharpen and make it too big. The advantage of the hollow grind is the blade will still register against the stone with the same angle, so it's easier to do a light touch-up of the edge.
Whatever medium you are using you’ll need to periodically flatten them unless you are using sandpaper which you just replace.
Mark stated that a cheap plane blade with weak metallurgy will work just as well as an expensive plane, the only difference being that with the cheaper variety you’ll have to sharpen more often.
One test of final sharpness is to shave end grain. If you can get a nice shaving you’ve done a good job.
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