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. That's why we divided this article into two parts.
In part one of the article, we looked 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. If you missed it last month, you can read part one now. Or if you're ready, let's move on to part two.
Tip for holding the tool correctly
If you want to determine if you are sharpening at the same angle that the blade already has, try this easy trick. Mark the edges bevel with a black magic marker, then go ahead and do a stroke or two on the Japanese Water Stone.
Look at the edge. If you have matched the edge angle exactly, the magic marker will be scraped off along the entire edge bevel. If your angle is too high, only the marker near the very tip will be gone. If your angle is too low, only the marker near where the edge bevel meets the primary bevel will be gone.
The most common mistakes made when sharpening bonsai tools is an uncontrolled angle. The black magic marker will help you maintain a controlled angle.
Sharpening bonsai shears
Bonsai shears are relatively easy to sharpen. To properly sharpen bonsai shears, you need to open the blades as wide as you can. The problem with most bonsai shears is that the two blades are riveted together and you cannot get the blades apart for proper sharpening.
If your bonsai tool has a threaded bolt (sometimes it's a screw), carefully remove it and separate the blades. If your bonsai tool is riveted, don't worry, you can still sharpen the blades.
Wet your stone before beginning. Place the angled side of the blade on the stone. Tip the blade back and forth on the stone to make sure you have the right angle. Mark the beveled edge with a black magic marker. The objective is to hone the outside (angled surface) part of the blade.
To get started, open the bonsai shear and lay the angled surface flat on the stone. Starting at the tips, rest the blades on the stone, then push them away from you. Once you reach the end of the stone, pull the shears back toward you without making contact with the stone.
Article you might like - Bonsai Tips for Summer Care
It's like trying to take a thin slice of the stone. Try to maintain the original angle established by the manufacturer and to keep each honing stoke parallel with this angle.
This is repeated several times to hone the edge of the blade. To make sure you are maintaining the correct angle, look at the edge. If you have matched the edge angle exactly, the magic marker will be scraped off along the entire edge bevel.
Use one straight motion when sharpening. Do not "scour" back and forth. Use numerous smooth strokes, moving the blade in one direction toward the tip. Many light strokes are better for the blade than one heavy stroke.
The bulk of the sharpening is done to the outside or beveled edge. If the cutting edge is neglected and pretty blunt, you will have to remove a lot of material.
Rub the bevel across the stone until a burr is obtained along the full length of the edge. The presence of a burr is easily felt by drawing a finger at a 90 degree angle across the back of the edge of the blade.
As soon as the burr is detected, transfer the blade to the finish stone (if using a Japanese combination stone) and alternately hone the bevel and back side until the burr disappears. This should only take a couple strokes. Remember, the bulk of the sharpening is done to the outside or beveled edge.
The presence of the burr means that the steel is thin enough at the top that it is folding over slightly, because the bevel you've just ground has reached the edge tip. If you stop before the burr is formed, then you have not ground all the way to the edge tip, and your bonsai shear will not be as sharp as it should be. The forming of the burr is critically important - it is the only way to know for sure that you have sharpened enough.
That's it. You should now have sharp bonsai shears. Despite these recommendations, if you still don't lubricate your tools regularly, they will rust. Apply lubricate to any moving parts. Then store tools in a dry place. By following these steps, your tools will be ready whenever you are, any time of the year.
Sharpening concave cutters
For curved blade tools such as knob or concave cutters it's a little harder. This requires a little more experience. I certainly don't recommend practicing your skill on an expensive pair of cutters, but you can certainly do this yourself. Take your time and look closely at how your cutters are made before you begin.
The first step in sharpening concave cutters is to use a cylindrical stone to sharpen the interior surface. The objective is to remove as little material as possible with your stone while keeping the original bevel.
Don't try to change the angle or fix your tools bite. The two sharp edges on your cutters should meet exactly. One edge should just barely overlap the other so that when they snap through a branch one edge will not jam into and dull the other. They should close so precisely that you cannot see any light between the edges when they are closed.
Take your time and sharpen the inside until you can feel a burr. Once you feel a burr, it's time for the water stone. Lightly roll the outer part of you concave surfaces against the stone, one side at a time.
All your trying to do is smooths the surfaces and remove the burr. Again, Do not attempt to correct the "overbite" of concave tools. After sharpening, apply light coating of oil to prevent your tools from rusting.
Adjusting the action of hinged tools
If you need to adjust the rivet to keep the closing tension tight, it may be tapped lightly with the "peen' side of the hammer. For best results, the tool should be held firmly against an anvil or piece of heavy metal.
Don't hit the joint too hard. You don't want your bonsai tools to open and close too tight. The blades should have enough freedom to move easily while maintaining a close cutting distance between themselves.
How do you know if the tool needs to be replaced?
If you have sharpened a tool several times, you may notice that the cutting edge is becoming rounded. This may mean the blade or tool needs replacing rather than sharpening to maintain a clean clipping action.
Final touches with Choji oil
Triflow [and choji] are inexpensive oils that, when applied to the surfaces, insulates the steel and prevents it from oxidizing. Whichever way the oil is applied, keep the coating thin so it won't drip off the tool head and onto the floor. Excess oil should be wiped away. Remember, regularly cleaned and oiled tools will not rust - which is important after all your heard work spent sharpening them.
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.