Techniques for Grinding: Sharpening Work Tools
To grind a badly blunted chisel or plane iron, before finishing on an oilstone, hold the chisel or plane iron at an angle of 20° to 25° to the wheel. The rotation of the grindstone should be towards the blade edge.
Take care to prevent burning at the edges of the tool during grinding as burning and overheating can affect or ‘draw’ the temper of the steel and cause it to soften. This will reduce the effectiveness of the cutting edge.
To avoid this, the edge should be ‘quenched’ frequently in water to cool it. The efficiency of edge tools depends on a hairline of sharp steel.
Move the bevel from side to side on the grindstone, keeping a light pressure. It is advisable to use a gauge, against which you can rest the tool, to obtain the correct angle. Otherwise the bevel may become convex.
There are two angles in grinding-the primary angle, or the rough edge, and the secondary angle, or sharp edge.
A blade is ground by moving it in a figure-of-eight motion on the stone, to produce a ‘wire edge’. This is an edge of metal which can be taken off by rubbing the flat of the blade flat to the surface of an oilstone, using a few firm strokes.
Always keep oilstones clean and moist. Kerosene may be used to clean stones. If allowed to dry, they become hard and brittle and will readily become clogged or smooth. If stored in a dry place, keep them oiled and in a covered box.
Any irregularities or glaze (smoothness) may be removed by grinding on the side of a grindstone or by rubbing down with a wet sandstone.
Small, shaped oilstones, called ‘slips’ or ‘slipstones’ are used for sharpening curved cutting edges, such as gouges. Oil should be used as a lubricant.
10. November 2011 by admin
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