Tips on Sharpening

It has taken me some time to find good ways to use the different sharpening abrasives. Here are some of the techniques Iíve developed.

Producing a Flat Surface

In order to take a full-width, very thin shaving, the blade of a smoothing plane needs to be almost straight rather than cambered (curved). This straight edge can only be formed by the intersection of two flat surfaces, so it is essential to be sure that the waterstones, oilstones, or other honing abrasives are kept flat.

When I sharpen with waterstones, I flatten the stones every time I sharpen. Frequent flattening helps keep the blade surfaces flat. Postponing stone flattening means that the blades become slightly cambered at first, then more and more cambered until the stones are flattened and remedial work is done to true up the blades. Itís less work in the end to touch up the stones often so that the blades never become cambered. (Other types of plane work better with a cambered blade, but I wouldnít try to use a dished-out stone to produce the camber.)

My favorite method for flattening waterstones is to use a granite surface plate and wet/dry sandpaper. The granite plate has a flatter surface than the diamond stones Iíve used, and its larger size makes it easier to use. When the sandpaper loses its bite, sprinkling some loose silicon carbide abrasive on it will make it cut again. This is much less expensive than using a fresh sheet of sandpaper. For finishing stones, I use finer sandpaper (400 or 600 grit) and donít add loose abrasive because I donít want the coarser abrasive to embed in the finishing stone.

Oilstones need flattening too, but not as often.

The cast iron lapping plate I use with diamond paste has worn a very small amount, maybe even less than my oilstones. I have re-flattened it only once since I started using it, and it took very little time. After it was flattened, the edges it produced were not quite as sharp for a little while, probably because of embedded grit from the flattening on waterstones. After several blades had been honed on it using fine diamond, it began to produce sharper edges again.

 

Lubricants for Oilstones and Diamond Paste

The light oil usually recommended for oilstones can be a problem in a shop where wood surfaces need to be kept clean. I have had good results using odorless mineral spirits (paint thinner) with both oilstones and the cast iron plate for diamond paste.

 

Getting a Waterstone to Bite

Sometimes a blade just skates over a waterstone without being abraded. On coarse stones, adding a little loose silicon carbide abrasive will help to loosen up some grit from the stone, forming a slurry that will abrade the steel.

On medium and fine stones, using a nagura stone to develop a slurry helps speed up cutting.

 

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