On this page, we introduce the techniques of sharpening Japanese plane blades as practiced by professional Japanese carpenters. The methods I share are the result of extensive trials and errors with my own hand planes. Some techniques may seem specialized, but I assure you that this guide will significantly enhance your craftsmanship skills. Let’s enjoy the world of woodworking together!
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日本語版の記事（鉋（かんな）の研ぎ方【プロ用】鏡面仕上げを大工が解説）はコチラ
List of Contents
Article Author
Kentarou Fukata
A Kyoto, Japan native born in 1985, I am a seasoned carpenter boasting five national qualifications in housing-related disciplines in Japan. Committed to the dissemination of carpentry expertise, I actively contribute to professional development within the field through instructional content on YouTube.
Intro Video: Mastering Plane Blade Sharpening
Complementing the guide is an informative video designed to augment comprehension.
If you wish to utilize features like subtitles, please reopen the video on YouTube. You can access the subtitles through the ‘CC’ button on the playback screen or in the settings.
This video presents an actual demonstration of sharpening a hand plane blade. Please observe the posture and flow in this visual guide.
Characteristics of Japanese Plane Sharpening
Three key points for sharpening hand planes
Thorough Resharpening
Hand planes require an absolute sharpness. In the working environment of hand planes, they are often used until the edge becomes dull. The worn blades must be completely ground down using a coarse whetstone.
Creating High-Precision Shapes
The effectiveness of Japanese hand plane blades hinges on their sharpness and the creation of high-precision shapes. The method introduced here involves polishing both sides of the blade to perfect flatness. This is crucial to ensure consistent performance when preparing multiple planes for precise woodworking tasks.
Absolute Sharpness
Absolute sharpness is a requisite for Japanese hand planes. The sharpest edge is one formed by two mirror-polished surfaces. However, finishing whetstones used for mirror-finishing are extremely hard and resistant to wear. Therefore, considering the points mentioned above, skillfully differentiating between coarse whetstones for resharpening and finishing whetstones for mirror-finishing becomes indispensable in the sharpening process of hand planes.
Overview of the Sharpening Process
Sharpness Benchmark
The target sharpness for a hand plane blade is such that it can smoothly shave arm hair, akin to a razor. However, this isn’t a direct comparison. Considering that the blade angle of a razor is about 28 degrees while that of a hand plane is around 33 degrees, achieving this level of sharpness with a hand plane necessitates more refined sharpening techniques.
Time Required for Sharpening
It typically takes me about 20 minutes to sharpen a single main blade of a Japanese hand plane. This duration can vary depending on the wear condition of the blade and the desired level of sharpness.
Choosing Whetstones for Plane Sharpening
I use King brand whetstones for chisel sharpening, but for hand planes, I primarily sharpen with Shapton brand stones. The reason for this choice is that although both are synthetic ceramic stones, they differ in wear rate, sharpening feel, and optimal usage conditions based on the manufacturer. After comparing and testing, I’ve settled on my current selection.
Let’s illustrate the characteristics of whetstones necessary for sharpening hand planes by highlighting the differences between King and Shapton whetstones.
Differences between King Whetstones and Shapton Whetstones
Regarding King Whetstones
King brand whetstones from Japan are characterized by their need to generate swarf (sharpening slurry) to sharpen effectively. In sharpening Japanese blades, this slurry acts as an abrasive. However, without this slurry, neither the blade nor the King stone will wear. As a result, at the stage of generating swarf, King stones tend to be unable to maintain the flat surface necessary for sharpening hand planes. This characteristic becomes problematic when using multiple stones.
Characteristics of Shapton Brand Whetstones
A significant feature of Shapton brand whetstones from Japan is their ability to sharpen blades starting from a slurry-free state. This means that after flattening the stone, a process known as “surface correction,” Shapton stones can be used immediately. This ensures a smooth transition to finer grit stones without compromising the flatness of the blade or the stone.
However, Shapton whetstones are also characterized by their tendency to snag during strokes when swarf is generated, necessitating frequent “surface corrections.” Therefore, for sharpening blades other than hand planes, where perfect precision is not paramount, King whetstones are more suitable.
Differences in the sharpening feel between the two whetstones
The sharpening sensation of the King whetstone resembles kneading fine grit with a blade, evoking an impression similar to natural whetstones. It possesses strong surface tension, leading to excessive adherence during flat sharpening. Regarding the wear rate, the more grit is produced, the more pronounced the sharpening wear becomes.
The sharpening feel of the Shapton whetstone is likened to filing with a viscous file. Its surface viscosity allows for smooth gliding across the whetstone even when it sticks due to surface tension, making it suitable for flat sharpening. As for the wear rate, the condition immediately after flattening sees the most significant wear for both the whetstone and the blade.
Systematic sharpening with series whetstones
Shapton offers a line of whetstones with fine, progressively finer grits, similar to sandpaper. This allows for efficient refining of the grit as you transition to progressively finer levels. Shapton whetstones are available up to an ultra-fine #30,000 grit, providing the necessary range for efficient sharpening. This ensures a consistent sharpening feel all the way to a mirror finish.
About Natural Whetstones
Natural whetstones, unlike synthetic ones, are quarried from natural sources. They are significantly more expensive than synthetic stones. Some enthusiasts believe that the duller finish of natural stones provides a better edge, but this is a misconception. The ultimate sharpening limit is a mirror finish, physically. The high price of natural stones is due to their rarity, not necessarily their ability to produce a sharper edge.
Tips for Maintaining Flatness in Sharpening
Points for Sharpening the Blade Back
The back of the blade should be sharpened to a perfect flatness. However, the purpose differs from chisels; the aim is to sharpen the blade edge. It’s functional as a plane if just the blade’s edge part is flat. When sharpening the back, pressure tends to be applied more towards the blade’s root due to hand habit, but it’s essential to sharpen towards reducing the blade edge. Concentration is needed to apply pressure on the edge during sharpening.
A tip when using multiple stones to sharpen the back is to deepen the blade on the stone with each increasing grit. This helps the stone to contact the blade edge more easily if the back is slightly concave from the edge to the root. If the back is convex from the edge to the root, just support the edge with its weight.
Points for Sharpening the Blade Face
Sharpening the face of a plane blade doesn’t necessitate learning the strokes by muscle memory as you would with chisels. Instead, it’s about maintaining a balance, as if the blade is standing on the whetstone, and keeping its center of gravity steady throughout the stroke. Your dominant hand should control the tip of the blade with your index and middle fingers, while your little finger provides support and lift. The other hand aids by pressing down on the blade’s edge. As long as the center of gravity remains stable, you can effectively sharpen the blade by allowing it to glide across the stone.
This technique is attainable for anyone. If you find balancing tricky, sharpening with just your dominant hand can make the center of gravity more discernible. Mastering this ‘sense of supporting the center’ enables you to evenly sharpen the blade.
How to Use the Whetstone
When sharpening a standard-sized plane (with a 70mm blade), approach the whetstone by dividing your focus and sharpening each half individually. Glide the blade longitudinally, back and forth. As for the lateral movement, for right-handers, guide it from left to right. Begin by conditioning the whetstone with the blade’s base (the non-cutting metal part), creating a mental picture where the base prepares the stone before the cutting edge makes contact and is sharpened. After completing one comprehensive stroke across the stone, ensure to flatten the whetstone before initiating the next stroke.
About the Sharpening Process
When sharpening, applying pressure generates a slurry based on the grit of the whetstone, which then wears down the blade, resulting in a surface finish corresponding to the grit.
The technique of pulverizing these particles to achieve a finer finish than the original grain size of the stone is known as ‘finishing sharpening.’ The method involves first creating a slurry through normal sharpening, then reducing the sharpening pressure to crush the slurry particles. Subsequently, only the pulverized slurry is used to refine the blade’s edge.
Note: Especially with natural stones, there’s an ease in breaking down the particles.
However, this finishing process wears the stone’s surface unevenly, which can interfere with the consistency needed when transitioning to a finer stone. Therefore, finishing sharpening is reserved solely for the final stage of sharpening.
Sequential Steps for Sharpening Hand Planes
n this section, I will detail the process of sharpening hand planes, including an introduction to the whetstones I use. Note as a premise that it’s quite rare to sharpen the backside of a hand plane blade with a coarse whetstone. Therefore, in the initial stages, the focus will be solely on sharpening just the surface of the blade.
Here is the demonstration video from the viewer’s perspective.
Rough Grinding Essentials in Sharpening
Coarse whetstone made of metal sand (No. 250)
This coarse whetstone is ideal for shaping the blades of carpentry tools. Since the face of a hand plane blade is about five times larger than that of a chisel, using the red whetstone (grit 1000) meant for chisels is too time-consuming. While the coarse whetstone is handy for quickly wearing down the blade, shaping the blade to the desired form is a challenging skill. Sharpen the blade edge by applying pressure until a clear burr (a flipped edge) forms. As the whetstone’s surface and the blade’s shape are prone to distortion, proceed with careful attention.
Rough and medium stones lack slipperiness, so rely on the center of gravity while sharpening. In my opinion, this stage of sharpening with the coarse whetstone is the most challenging step in the hand plane sharpening process.
Red Stone (Grit 1000)
This is a standard intermediate finishing whetstone widely used by carpenters. Similar to the coarse stone sharpening process, focus on sharpening the blade until the surface reaches 1000 grit (until the scratches from the previous stone are gone). If a flat reference plane is not established on the blade edge at this stage, it’s impossible to correct the sharpening quality in subsequent steps.
Note: If the blade edge isn’t sharpening well, revert to the previous step and sharpen again. During plane sharpening, wash away any particles other than the sharpening slurry with water. Each time you flatten the whetstone, thoroughly clean the whetstone, blade, and hands with a household water sprayer.
Method for Flattening Whetstones
Flattening of Coarse Whetstones
Both coarse whetstones and intermediate finishing stones are flattened using a block. Introducing sand between the whetstone and the block accelerates the wear. Rubbing a grit 150 gold sand made coarse whetstone against the block is also an effective method I recommend.
Flattening of Shapton Whetstones
In later stages, I personally use a diamond whetstone (grit 150) on all my Shapton stones. Flattening in a consistent pattern ensures the whetstone’s surface aligns with the next one to be used.
Note: When flattening with a diamond whetstone, rubbing too forcefully might distort the shape of the whetstone. Therefore, gently rub the stones together to even out the surface.
Intermediate & Final Stages of Sharpening
Sharpening with Shapton Green (Grit 2000) & Shapton Orange (Grit 5000)
These stones are well-suited for sharpening hand planes. The sharpening method for both Grit 2000 and Grit 5000 is similar to that of the rough stone. Shapton stones should be easier to sharpen due to their slipperiness. However, as the grit increases, the stone’s abrasive power decreases, making it challenging to correct any misalignments on the bevel. If you notice a misalignment, revert to the previous stone.
Dealing with the ‘Ears’ (Edge Corners)
When sharpening planes, the edges of the blade (‘ears’) can form sharp corners, so it’s necessary to process these areas with a rounded finish. You can sharpen the corners on the same stone you’re using, but having a dedicated stone for this task simplifies the process. Sharpen these rounded areas as you would the blade edge, ensuring sharpness.
Sharpening the Blade Back
At this grit stage, it’s also time to sharpen the blade back. Alternate between sharpening the front and the back, removing any burr and checking for scratches on the back. The removal of the burr indicates that the sharpness is comparable to that of a chisel. Note: As burrs are metal, ensure they don’t contaminate the subsequent sharpening process.
Sharpening with Shapton Cream (Grit 12000)
This extremely hard stone with fine particles is sufficient for finishing hand planes. Although the Shapton Purple (introduced later) is more expensive, I recommend this stone as a more affordable option. The sharpening method for the Cream is the same as for the Green and Orange. Focus intensely on the blade edge, ensuring it matches the 12000-grit surface.
Mastering Final Touches in Blade Sharpening
Sharpeningwith Shapton Purple (Grit 30000)
The finest artificial stone available globally. First, sharpen as you did with the Cream to form a 30000-grit flat surface on the blade. After flattening, proceed to ‘finishing sharpening.’
Being the final stone, sharpen with the Purple to produce a slurry, which is necessary for the finishing process. Unlike the Green, the Purple stone is very hard, preventing slurry clogging and snagging. Gently crush the slurry while focusing on both the front and back of the blade edge. Continue sharpening until satisfied with the sharpness.
Rust Prevention with Silicone Spray
Blade edges can rust quickly, so immediately apply oil after sharpening for rust prevention. The type of oil doesn’t matter, but I prefer using easy-to-handle silicone-based spray oil. A little goes a long way; too much can make the next sharpening session slippery.
Characteristics of Horizontal Sharpening
Sharpening the blade by positioning it horizontally against the stone is known as horizontal sharpening. In Japan, vocational training schools often teach that ‘vertical sharpening is the basic,’ so horizontal sharpening isn’t commonly practiced.
Advantages of Horizontal Sharpening
The benefit of horizontal sharpening is that it tends to provide more stability during strokes, making it easier to maintain the flatness of the blade.
Note: This is presumably why the back of the blade is often sharpened horizontally.
Disadvantages of Horizontal Sharpening
A drawback of horizontal sharpening is that it results in the sharpening lines (scratches) being parallel to the blade edge on both sides, which is believed to make the edge more prone to damage. When practicing horizontal sharpening, it is particularly important to achieve a mirror finish to eliminate these lines.
From my experience, I have never had issues with the sharpness when sharpening horizontally with a Grit 30000 stone. However, if it concerns you, it’s worth exploring and mastering vertical sharpening as well.
Conclusion
Have you found useful insights on the Japanese plane sharpening process? I believe the method shared in this session represents the most consistent approach to mastering the hand plane, grounded in my personal experience. It’s important to note that even among Japanese carpenters, the tricks and techniques for honing Kanna (Japanese planes) blades vary widely. I encourage you to research and experiment with the diverse techniques from various masters, to discover the one that fits you best. This skill is bound to expand the horizons of your woodworking!