If you're serious about bonsai, you need to develop some basic sharpening skills. Dull or improperly sharpened bonsai tools can crush the stems and branches instead of cutting them clean, resulting in damaged plant tissue. Sharp tools will keeps diseases, fungi, and weed seeds from being unwittingly spread around your bonsai.
There are several areas of expertise when it comes to sharpening bonsai tools, which also means there's a lot to learn. So we've divided this article into two parts. In this article, we'll look at what tools need to be sharpened, how to recognize if your bonsai tools have a sharp or dull edge, and selecting a sharpening stone.
What bonsai tools need be sharpened?
Its true that not all bonsai tools need to be sharpened. In general there are two types of bonsai tools that need sharpening: those that cut, such as bonsai shears and pruners; and those that bite, such as concave cutters and knob cutters.
Each type of bonsai tool has different sharpening instructions, and it's important to follow the correct steps. But before breaking out the sharpening stone, check your manufacturer's warranty, if there is one. In most cases, sharpening bonsai tools will void the warranty.
The mechanics of a sharp edge
So how do you know if your bonsai tools have lost their edge? Try rubbing your thumb lightly - and - carefully across the edge. If the edge grabs into your thumb pad, then it's probably still sharp. To calibrate your thumb, test a known sharp edge like a new razor blade periodically, always being careful not to cut yourself.
The different types of sharpening stones
There are many good sharpening stones on the market today. However, if a stone is too hard for the job, you'll never get the desired edge regardless of how hard you work. If it's too soft, you can't control the amount of material taken off the tool.
At the Bonsai Outlet, we like to recommend Japanese water stones. They are softer than western style stones, and they continually expose a fresh, sharp surface to the tool's edge. In fact, when you use our fine crafted Japanese bonsai tools and combination water stones, you will immediately recognize why they are the best and why they should be in your tool kit.
Our combination water stone has 280 grit gray bauxite stone on one side, and 1500 grit white aluminum stone on the other. The coarser 280 grit stone can remove very small nicks and burrs. The higher the grit number, the finer the sharpening action. With a combination stone, you have course and fine grit on opposite sides - two stones in one.
The softer Japanese stones have a few advantages over harder stones. For one, they do not get glazed or loaded with the material they are sharpening. New particles are constantly exposed as you work with the stone, and thus they continue to sharpen consistently. Also, soft stones can be lubricated effectively with water rather than oil. So nothing but a bucket of water is required. Finally, the worn material and the water will help sharpen and polishes the blade. The only disadvantage is the obvious one. Soft stones wear out faster.
Using the combination water stone is easy. Thoroughly wet the stone by soaking it in water. Because water evaporates quickly, you'll need to keep the stone wet during the sharpening process by periodically applying more water to the stone surface.
Understanding burrs, bevels, and angles
Understanding your bonsai tools and what happens to them as they are sharpened is very important. Here are basic definitions:
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Burr: During the sharpening process, steel naturally forms a burr. The burr is a thin bendable projection on the edge of the blade. A blade with a burr is not what you want. To test for a burr, slide your fingertips lightly from the side of the blade over the edge. You will feel the burr drag against your fingers. Test from both sides, because burrs are usually bent over one way or the other. As your sharpening improves you should be looking for smaller and smaller burrs.
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Bevel: Think of a knife. Most knife edges are shaped like a V. The angle of the V is called the bevel or bevel angle. You'll notice that your bonsai shears are beveled differently than most knives.
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Angle: The smaller the angle, the less metal that's behind the edge and thus the weaker the edge. A surgeon's blade will have a very thin, very low-angle edge. Your bonsai shear will have something around a 30-degree angle. Don't be obsessed with getting the exact right angle. Rather, concentrate on holding it precisely. You don't want to change the angle on your bonsai tools.
Since tools are manufactured with the ideal bevel angle, the first rule in sharpening is to follow the existing bevel. The second rule is to remove as little metal as possible; this makes the tool last longer. Sharpening wears down tools much more than does normal use. So to make your tools last as long as possible, remove as little metal as you can each time you sharpen them.
To learn more, continue on and read Part 2.
DISCLAIMER: The content provided in this article is not warranted or guaranteed by Bonsai Outlet. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. Happy bonsai gardening.