How to Reshape & Sharpen the Blade of Your Japanese Hand Plane
Riho Egawa·August 30, 2022
Over time, blades will shorten as they are sharpened. When the edge of the blade shortens too much, you will need to re-shape and re-sharpen it in order to keep using it. Discover the traditional Japanese method of "ura-dashi" and "ura-oshi" to make your precious plane blade look brand new. You don't have to be a seasoned craftsman to follow these steps. Let's get the groove on!
In this article, we go over these important, easy-to-follow steps to help re-shape and sharpen the backside or "ura" of your hand plane:
1: Reshaping the Blade's Edge
Over time, blades will shorten as they are sharpened. When a Japanese hand plane blade shortens too much, you will encounter a condition called “ura-gire.”
To understand what ura-gire is, you need to look at the non-beveled side of the blade. There you will see a hollowed recess with a U-shaped rim along the bottom and sides of the blade, which is called the “ura.” Once the blade has been shortened to the point that the bottom of the U-shaped rim is no longer present, the blade will not be able to maintain a flat edge when sharpened.
To fix this condition, the U-shaped rim must be reformed through a process called “ura-dashi.”
2: Tools to Prepare
To perform the process of ura-dashi, you will need a small anvil with a rounded edge, a hammer, a metal plate secured with a wooden board, emery powder, a thin piece of wood for safely holding the blade, and water.
3: How to Perform the Ura-dashi
With the blade bevel-side up and the bevel facing away from you, lay the back side of the blade on the curved edge of the anvil.
Position the blade so that the bevel meets the edge of the anvil.
The center area of the bevel that is parallel to the blade’s edge is called the “jigane,” which is made of softer metal. This is the area that should be tapped out with a hammer.
It is important to be careful when tapping the bevel to avoid striking the edge of the blade, which will likely cause it to chip.
Make sure that the hammer strikes directly over the contact point between the blade and the anvil.
If done correctly, you should hear the same dull metal sound as can be heard in this tutorial video. This sound indicates that you are tapping the correct location on the bevel.
It is also important to avoid tapping one spot at a time. Instead, tap evenly across the blade's bevel. However, if the U-shaped rim, or ura, on the non-beveled side of the blade is only partially missing, you should focus on tapping the area that needs reshaping.
4: How to Perform the Ura-oshi
After tapping out the "jigane," the next step is to sharpen the blade's edge with a process called “ura-oshi.”
With ura-oshi, you grind the non-beveled side of the blade until it's completely flat and the U-shaped ura shines like a mirror.
To start, place a half teaspoon of emery powder onto the metal plate and add three drops of water to the powder. Adding too much water will cause the emery powder to spill over the plate and unnecessarily extend the amount of time it takes to complete the sharpening process.
Once the powder and water have been added, place the non-bevel side of the blade on the metal plate. Then place a thin piece of wood on top of the blade and hold them together to secure the blade as you begin moving it back and forth over the emery powder.
Continue to grind the blade with a back-and-forth motion, using all areas of the metal plate, and make sure there is absolutely no gap between the blade and the plate during this process.
Keep grinding until the sound completely disappears and the emery powder is dry.
Once you are done with the ura-oshi process, check the non-beveled side of the blade to see if the U-shaped ura has been successfully reshaped and is shiny.
5: Checking & Reshaping Again
If the ura is not smooth and shiny, then start the ura-oshi process over again by adding more emery powder and water to the metal plate and grinding the blade until you achieve the desired results.
If, after continuing the grinding process for a while, you are still not able to form the U-shaped rim on the non-beveled side of the blade, then it's likely that the initial reshaping process was not done enough. If that is the case, you will need to go back to the reshaping stage and tap out the jigane some more with a hammer.
6: Ready to Sharpen
Once you have a shiny, mirror-like appearance and the correct U-shaped ura, you can begin the process of sharpening the blade by starting with a low-grit whetstone.
Check out our other articles for more great tips on how to care for and maintain your Japanese hand planes!