Restorer's Notebook

Sharpening Chisels and Plane Blades

 Chisels


Often the wear on the lapped side of the blade is overlooked in the sharpening of chisels and planes. Imagine what the edge looks like when worn. It will show roughly equal wear on either side of the edge: the side where we grind and sharpen, and the bottom of the chisel. Having any kind of rounding on the reference surface (the bottom) will force you tip up the handle so the edge will bite.  While this might be acceptable in a plane, this condition in a chisel  makes cutting straight all but impossible. In order to truly sharpen the tool, the tip must be ground down so there is no wear visible on the lapped side. This can be done grossly by making the grinding angle quite large so, though it is taking only a small amount of metal, it is quickly grinding the edge back until the wear is gone. Less heat will build up that might otherwise ruin the temper of the steel. After the wear is ground back the cutting angle can be restored.


I think the bevel angle is the least important of the parameters of sharpening. Having a flat bottom surface is first. Having any grind that removes the dullness is next. Third is having the bottom and the bevel polished mirror bright. Only in special circumstances are specific bevel angles important, i.e. end-grain, soft wood, erratic or contrary grain.


Planes


Plane blades can have micro-bevels on either side of the cutting edge because they are fixed in the plane body. This means that a very slight bevel on the flat side can be made using a very fine stone eliminating the need for polishing the entire back of the plane iron. While most of my plane irons have polished backs, some old irons that were pitted from rust were improved immensely by adding a micro-bevel.



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Back Cutting

 Marking gauges and molding planes have a tendency to wander as our arm motion is not uniform and often the grain pulls the blade. This can be avoided by not trying to make the mark in one pass. Rather, the mark should be made in smaller increments, starting at the end and working up. In the case of a marking gauge, by starting the cut close to you and pulling the gauge toward you then moving a foot farther and pulling that into the first cut and so on up the board, you will always be starting with cutter newly aligned to the board. Should you stray, it’ll be for a small bit and it will end where the previous cut started, hopefully correctly aligned.

Molding planes similarly should start at the end of the cut and work backwards. You will always be reregistering the plane and getting a consistent cut.

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Inpainting

It is the perfect word. IN-PAINT: PAINT IN-side the limits of the  repair. Often professionals and amateurs alike try to "blend in" the repairs to the surrounding surfaces, increasing the repair area. It is better to match the repair to the surrounding surface using pigment and dye, careful not to go over into undamaged areas. Color matching at best is impossible. We can only approximate the color and sheen that aged wood and aged finishes have acquired over time using dyes and pigments. It is better to keep our repair area as small as possible so our less than perfect color match is at least as small as it can be. 


This concept can be expanded to include limiting sanding to the repair area only. Sanding around the repair until the  surface patina has be sanded off,  will make the wood go back to its un-oxidized color. For light woods like maple or cherry that have darkened, the sanded area will become lighter. Dark woods like mahogany and rosewood, especially rosewood, which will have acquired a beautiful orange patina, will darken considerably. All could be avoided if the repair is surfaced only within the repair area. Sandpaper may not be the optimal tool. Small scrapers might offer better control.


While replacement of lost material is common, by keeping the repair and subsequent color match confined, the repair will be less noticeable and, even better, less original material is lost.

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