What you need:
Round file - This should be sharp, match the size of your chain, and fit into the filing guide. The most common sizes are 3/16, 5/32 or 7/32 of an inch in diameter. If you are unsure, check your owner’s manual. It is best to replace your round file after every 5 sharpenings. To ensure sharpness after use, coat them in lightweight machine oil and keep them in a cloth so they don’t hit other objects and dull.
Depth-gauge guide and flat - The depth gauges are rounded parts that are in front of every cutter that go upward and almost seem to reach the top of the cutter edge. You want your raker to be about 1/10 of an inch lower than the cutter. If it is closer than that, then you need to file it down with a flat mill bastard file.
Vise - This will hold the blade of the saw in place on a solid surface.
Let’s sharpen things up!
First of all, make sure you know the size of your chain’s saw. Next, you should clean your chain. You can do this by using a brush and some sort of commercial degreasing detergent to get rid of any objects or oil. Once you have your chain clean, inspect it for any run-down or busted teeth and links. Look at the flat surface at the top of the cutting teeth. Is it at least ¼ of an inch in length? If not, your chain could break during use, so you should just be safe and get a new chain.
After inspection, secure the blade of your saw in a vise on top of a solid surface as shown above. This security will make filing easier. Then you want to have a starting point so you aren’t filing your chain all day long with no end in sight. Typically the shortest cutter, or leading cutter, on the chain is the starting point. If they look all the same then you can just pick any cutter, just mark it with something like a permanent marker. The bottom line is you want all of the cutters to be about the same length. This way your chainsaw will cut into things smoothly and easily.
Now the filing can begin! Put your round file into the notch on the front part of the cutter. The round curve file should fit this angled tooth. About 20% of the file should be above the top of this tooth, which you can see below. Then check the angle you should file on your owner’s manual. It is usually 25 or 30 degrees. You can push the file either way though most prefer going towards the cutter’s point. Twisting while filing will get rid of the small metal bits and give you a smoother cutting surface.
This is the cutter and where you want to sharpen it.
As you move from tooth to tooth, keep the one you are filing on top of the blade. Once you have filed all of the teeth, and they all look of similar height, it is time to move onto the rakers. Now it is time to check the depth gauge which are the hook shaped links in between the cutters. If they are not lower than the cutters by a tenth of an inch, they should be filed with the flat tool listed above. The last step is to check the chain’s tension and oil it, then you are good to go.
If you are more of a visual learner here is an awesome informative video: http://www.youtube.com/watch?v=PxrhQv6hyfY
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