The Shapton Kubo for Professionals is a tool that allows you to achieve a perfectly flat and true edge.
A good cutting edge results from the straightest, cleanest, intersection between the bevel and the flat back of a cutting tool at an acute angle. But when sharpening a plane iron, the process of removing steel for a new edge also deforms or hollows the surface of the stone. So with every sharpening session, the straight and flat edges of the iron are also progressively lost. To achieve a really sharp edge takes experience, time, and effort. So it is important to keep the variables to a minimum and to keep both the edges of the irons and the surfaces of the sharpening stones as straight and flat as possible.
Note: We use here the word “plane iron". But these directions of course apply equally to chisels and other straight-bladed cutting tools like spokeshaves and the like. With knives, the flatness of the sharpening stone is not so important, though one should be careful not to allow the stone to become too hollowed. In these directions, flattening and polishing the flat side of a plane iron is not directly described, but it is a similar process and so these directions can be applied to the flat side of tools in the same way it is applied to the bevel.
- Plane iron: Flat side (only straight and flat is good!)
- Plane iron: Bevel straight (good!)
- Plane iron: Bevel rounded (bad!)
- Plane iron with straight bevel on a flat sharpening stone (good!)
- Plane iron with rounded bevel on a hollowed sharpening stone (bad!)
When working with the combination of Shapton’s ceramic stones and the Kubo flattening plate, it is possible to achieve an absolutely flat and true edge on plane irons and to keep the sharpening stone flat and true as well. Experience a truly flat and straight edge, such as you have never known!
Description and functions of the pieces
- Kubo in rubber box
- Rubber box top view
- Rubber box bottom view
- Flattening plate in cast bronze
- Surface A - electrolytically diamond-encrusted to surface sharpening stones
- Surface B - electrolytically diamond-encrusted to surface for tool blades
Note: Be careful not to drop the flattening plate on the floor or subject it to other shocks or stresses as the plate can be damaged and lose its flatness.
- Surface to flatten sharpening stones
- Direction to pass the stones over the surface
- Flattening action on the stones
- Surface for flattening plane irons or chisels
- Direction for flattening irons
- Flattening action with irons
- The Kubo rubber box, when closed, can be a very stabile base for sharpening stones
Flattening sharpening stones
Lay the flattening plate on a stable base. The A-surface for dressing stones should face up. Wet down the surface of the flattening plate. The water stones that need to be flattened also need to have been given time in a water bath, just as if you were going to use them to sharpen a blade.
- Lay the hollowed sharpening stone, which has been allowed to absorb enough water, on the A-side of the flattening plate.
- Make several passes of the stone with moderate pressure over the flattening plate, and then turn it 180 degrees and repeat the same process. Repeat the process evenly in the two directions until just enough material has been removed from the stone to leave it completely flat.
- Next, pass the stone over the plate with very light pressure. The last step is to very slightly “break” or “relieve” the now very sharp edges of the stone.
If you have several stones of different grit sizes to flatten, rinse the flattening plate well with clean water before changing to another grit size. If you have stones with a very fine grit size to flatten, work very carefully to keep the flattening plate clean and free from larger grits that can get embedded in very fine stones and spoil their polishing action. On very fine-grit stones, use as light a pressure as possible.
If you use coarse grit stones on the flattening plate, the diamond coating gets worn down relatively quickly. So we advise that if you want to flatten very coarse stones, it is better to rub two coarse stones together or to use a plate made of silicone carbide
. This concerns stones with a grit coarser than 500.
Flattening plane irons and chisels
Lay the flattening plate on a solid base. The B-side for flattening bladed tools should face up. Wet down the flattening plate thoroughly. Work only by pushing the iron over the diamond surface with moderate pressure, moving the iron slowly so that it does not deform. It is important to use, as much as possible, the entire surface of the stone, and not just one area.
- The surface on the left, about 80%, is used for normally-sized irons.
- The non-perforated area to the right, about 20%, is for small plane irons and blades that might be damaged if they catch an edge or corner in the perforations, or for blades with curved cutting edges.
- If you want to correct an iron that has a curved edge, or a rounded bevel, then you need to start by leveling an oval centered in the bevel of the plane.
- By passing the iron at a constant angle over the diamond plate, this oval is slowly and progressively enlarged.
- In this diagram you see the results of a completely flattened bevel as the oval is enlarged to include all the edges of the iron.
The B-surface for irons is not designed to remove chips in the edge. To do this, start with a coarse grinding stone.
The diamond face for correcting the bevels on plane irons is designed to finish surfaces that are already almost flat. If you use this surface often for coarse grinding, then the diamond abrasive coating will be very quickly, and unnecessarily, used up. So use this side, the B-side for dressing irons flat, only to finish flattening and perfecting the edge.
Also be careful when using the iron flattening side (B-surface) not to damage the surface with the corner of a plane iron. The diamond particles in the relatively soft (compared to tool steel) nickel coating can be lifted off. You should be particularly careful with narrow irons, like those for plow planes and mortice chisels, in this respect.
For coarse work to remove a lot of material, use a coarse stone!
The following drawings show how to cross-sharpen a plane iron. By using this technique, the bevel of a plane iron can be easily straightened. Sharpening using the method in these drawings is called in Japanese "yoko-togi" "Yoko" means cross, "togi" is the basic form of the word for sharpen. It means that the plane iron is held perpendicular to the length of the block, and the bevel is then moved along the axis of the block. Using this method, it is easier to move the iron steadily, in even contact, over the diamond abrasive. In the West, the tradition of moving the blade with its wide edge forward back and forth the length of the stone contributes to the formation of a rounded bevel, as it is very difficult to maintain a constant angle when holding the iron free-handed.
- Basic position for holding the bevel of the iron against the stone along its axis, or length wise.
- Movement direction. It is in this way that a Japanese iron is held and moved over the plate.
Sharpening - an example
The steps involved in sharpening an iron are different depending on the condition of the edge.
If the edge is just dull, start with step D.
If the bevel is rounded, start with step C.
If the edge is in very bad shape, very worn and/or with chips, start with step B.
- Flattening the sharpening stone: Use the A-side of the flattening plate
- Grind out the chips or other problems back to a clean bevel at the proper angle: Use a coarse stone until the problems have been ground away. Compared to a medium or fine stone, the coarse stone quickly wears to an uneven surface, and so does not work very well to achieve a good flat surface on the iron. Do not use the flattening block for this job!
- To cut the flat surface on an iron or chisel: use the B-side of the flattening plate.
- Sharpening: Use a sharpening stone of medium grit - a 1000 grit stone - for example, and be careful as you work that the more or less flat surface you created in the first step does not become rounded or deformed as you use the finer stone to improve the surface. If an iron with a flat and true bevel is sharpened, it should be sharpened over the entire surface of the bevel, and this should not be overdone. If the iron spends too long on the stone, the stone will begin to wear (to become hollowed) which will in turn begin to deform the bevel of the iron (to round it). In order to prevent too much wear on one stone, Shapton recommends the use of at least two stones with different medium grits. This could be stones with a grit of 1000 and 2000 grit, for example.
First honing: Use a stone with a fine grit, be careful to maintain the flatness of the stone, and pull the iron over the stone. Again at this step, it is advisable to use two different stones with different grits, about 3000 and 6000 grit at this step. If the iron has been well honed to an evenly flat surface up to this step, it will tend to adhere to the stone, in a kind of water lock. Even if you take your hands off the iron, it will stand up on the stone.
Note:this is not only true for the very thick and short Japanese plane irons!
- Mirror finish: Take a stone starting at about 8000 grit. These stones tend to remain flat longer because very little of the grit is worn away in use.
Enlarged representation of the electrolytic diamond coating. After long use, the diamond coating of the stone becomes worn. (see the diagram). If this happens, the old diamond/nickel coating can be removed at the factory and the plate re-coated as new.
- Diamond grit or abrasive
- Nickel plating
- Cast bronze