Tools: Sharpening

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When youíre in a hurry to get your pruning work done, you may not want to take the extra few minutes needed to stop and sharpen your tools. But itís well worth the effort for two reasons:
1) Your work will go faster and easier with sharpened tools.
2) The clean cuts you get with sharpened tools are healthier for your plants and trees.
Immediately after being cut, a plant oozes sap or resin, which dries to create a protective shield. But thatís just the beginning of the healing process. The plant also diverts energy from its growth to the damaged area while the wound is healing. Obviously, then, you want to help ensure that the tree will heal as quickly as possible. One way to do this is to make sure you create a smooth surface by a clean cut using a sharpened tool. Not only will the plant heal more quickly, and thus begin growing sooner, but it will be exposed to less damage from diseases, insects, fungi and weather extremes.
Following these steps will help you learn the proper way, then, to sharpen your pruning tools.
Step 1: Clean the blades
Whatever type of pruning tool you are using, clean the blade with a stiff brush and soapy water to remove any rust, clumped dirt or other debris. Dip the pruners in a solvent, such as kerosene, to clean off any sap. If youíve used your tools on evergreens, be sure to clean off the pitch residue using either oil or kerosene, too. After drying them, wipe the blades with a light coat of motor oil.
Step 2: Examine the sharpness
Examine the blade edge to determine the correct sharpening angle (usually about 10 to 15 degrees) (see Photo 1, at left). Itís also a good idea to check the manufacturerís guidelines for more specific sharpening instructions and cautions. Remember, for an anvil-type pruner, youíll sharpen only one blade but you must sharpen that blade on both sides.
The choice of sharpening tools is largely a matter of preference:
* Whetstones, the most common choice, offer many gradations and sizes, though you may find that a longer one is easier to work with.
* A diamond-coated flat file requires only water for lubrication, remains flat for fast sharpening and is durable enough to last a lifetime.
* A sharpening steel is useful for finishing or for a quick fix.
* Grinding stones require extra caution because they transfer friction heat that can affect the metal temper, making it more brittle.
Because the use of whetstones is the most common of these four types, weíll describe that technique in detail here.
Step 3: Begin grinding the blades
Start with a medium-grain whetstone (see Photo 2, opposite page, top). Thoroughly wet the stone by soaking it in water or a lightweight motor oil. (For an even lighter finish, some people prefer using a vegetable oil.) Because water quickly evaporates, oil is usually a better choice. It will not only act as a lubricant but carry away grit during the sharpening process.
To maintain the correct angle, press the blade against the concave side of the stone while sharpening. Use numerous smooth strokes, moving the blade in one direction toward the tipóas if you are trying to shave off a thin slice from the whetstone. Donít press too hard.
For every 10 strokes to the outer bevel, apply one stroke to the inner angle.
Keep the stone wet by periodically applying more water or oil. (Donít switch between the two, however. If you start with oil, continue using oil.)
If the blade has a nick, use a file to remove the bent metal piece. If it has multiple nicks, you may need to start the sharpening process with a coarser stone.
Step 4: Smooth the edges
Once youíve achieved the proper angle and sharpness, move to using a finer-grain whetstone and continue sharpening until you achieve a razor-sharp edge. Donít reduce the beveled edge to less than 1-mm thickness. A finer edge will not increase sharpening ability but will make the blade more fragile and prone to damage or breakage.
Step 5: Test the sharpness
You can conduct a preliminary test without having to make a trip outside. Simply hold the cutting edge up to a light source. If you can see light reflecting off the blade edge, itís not yet adequately sharpened.
Once the tool passes the light-reflection test, youíre ready for the ultimate test of trying it on the size of branch it is designed to cut (see Photo 3, at middle right). If youíve sharpened the blades properly, they will make clean, easy cuts. If the blades pull or catch, theyíre not sharp enough. In that case, continue sharpening with the fine whetstone or switch to an extra-fine stone. Retest as necessary, again being careful not to over-sharpen the blades.
Step 6: Add a coat of oil
Finish off the blades by rubbing a light coat of oil them (see Photo 4, bottom right). Remember: dirt that sticks to your tools acts as a sponge, collecting moisture and causing rust. So be sure to keep dirt off your tools when theyíre not in use.
When sharpening other types of tools, you may need to make some modification of these steps. For example, when sharpening anvil-type pruners or clippers, sharpen only one blade but on both sides. Avoid putting a curve on the bladeís edge. Unless the edge is perfectly straight, it wonít strike true against the flat anvil, and strands of plant tissue will cling to the blade after each cut.
Before sharpening shears, you might find it easier to take them apart. Keep in mind that regrinding blades usually is not recommended. Doing so tends to change the cutting angle and destroy the fluting. Plus, regrinding can create a convex cutting edge that leads to poor shearing action and difficulty in cutting.
For scissor-action "bypass" lopping shears, sharpen only the outside surface of each blade. This will maintain the cutting surface so the blades will cut cleanly as they slide past each other. Remember that the inside blade surfaces need to remain flat, so you should clean them but not sharpen them.
When youíre sharpening your tools, itís also a good idea to check the tension screw between the blades. If needed, adjust the screw to allow more freedom of movement while still ensuring that the blades are close enough together to work properly.
What if you have a saw that needs sharpening? Thatís a tedious job that takes special skills and special equipment, so youíll most likely want to leave it to a professional. Check the Yellow Pages under "Sharpening services" or try a local hardware store.
After youíve sharpened a tool several times, you may notice that the cutting angle is becoming rounded (an edge that is more than a 90-degree angle). At this point, the blades start working with a crushing action instead of a clipping action. This indicates the blade is worn out, and itís time to replace it or the entire tool.
Protect your investment in quality tools and limit the need for sharpening by performing routine maintenance between uses. Find a handy, easy-to-reach spot to hang up a rag thatís dry on one end and has oil on the other. Use it to wipe off your tools, keeping them clean and oiled after youíre done using them. Itís especially important to do this small task before putting away your tools for the season.
Another handy trick is to keep a 5-gallon bucket filled with coarse builderís sand in your garage or tool shed. Dip the metal blades of each tool into the sand and pull them up and down several times. This will remove any mud or clinging soil. Next, use a wire brush or steel wool to take off any rust or other particles of debris that remain. You also can pour some motor oil into the bucket of sand so that, when dipping them in the sand to clean them, you give them a coating of oil.
Despite these recommendations, if you still donít lubricate your tools regularly, at least do so at the end of the season, applying a light coat of oil to the blades. Also protect wooden-handled tools with linseed oil or a coat of varnish. And lubricate 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.