How To Sharpen a Chain Saw
Do you remember how your chain saw cut when it was new or last equipped with a new cutting chain? It should cut like that–or better–every time you use it. If it’s not cutting like new, you’re wasting time, damaging your equipment and putting yourself at risk.
Manufacturers design chain-saw cutting chains for easy maintenance. However, like most service tasks, to do the job right you must first understand the basic principles involved.
How saw chains work
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A saw chain comprises five basic parts:
1. left-hand cutters
2. right-hand cutters
3. tie-straps
4. drive links
5. rivets
Because the cutters do the work of slicing and removing wood fiber, they are the primary focus of our attention here.
Cutters have two distinct features: a ramp-like depth gauge, or raker, at the front and a gouge-like cutting element at the rear. The gulf between them is the gullet.
The cutting element has a profile that looks like the number “7”. Its two surfaces (the top plate and side plate) contain three different angles. The top-plate angle is the easiest to recognize. It’s the familiar 30- to 35-degree rake you see when you look down on the cutter. The bevel beneath the top plate is the top-plate cutting angle. Like a chisel, its optimum setting is 60 degrees. The third angle is the toughest to visualize. It’s the side-plate angle or the arc formed in the side plate. This angle typically is 85 degrees or less, depending on the brand and style.
Here’s how these angles combine to cut wood. The sharp corner, where top-plate and side-plate angles converge, slices across the wood grain. Alternating left- and right-hand cutters work on each side of the cut. The chisel-like angle beneath the top plate scoops out the chip. Cutters take turns biting as they “porpoise” through the cut at speeds approaching 60 miles per hour.
The depth gauge controls the depth of each “bite,” or thickness of each chip. Depth gauges typically are 0.025 to 0.035 inch lower than the critical corner. This difference is what gives the corner its ability to cut.
When to sharpen
Cutters are plated with a thin but tough coating of industrial chrome. They would stay sharp almost indefinitely if you always used them on clean wood. However, in the real world, wood often is dirty or laying near the ground where contact with dirt, rocks, embedded grit and other debris is difficult to avoid. At the high speeds of a chainsaw, it doesn’t take much to dull a sharp chain. That’s why prudent saw operators often brush, wash or chop off dirty areas before cutting. It can save a lot of time in the long run.
Several signals tell you when it’s time to sharpen:
* When the chain no longer self-feeds. This is the most obvious signal to re-sharpen. A properly sharpened saw chain pulls itself down through the cut. If you find yourself pushing on the saw to make it cut, or using the bucking spikes to apply heavy leverage, it’s time to sharpen the chain.
* When the saw’s discharge is dusty. A properly sharpened saw chain expels nice, square wood chips. If your chain saw is producing wood dust instead of chips, it’s time to sharpen.
* When the chain looks shiny. Look at the top plate and side plate. If the chrome plating has worn away, it will expose the steel underneath, and the cutting edge will be shiny. To restore the cutting edge, you must file the steel away until a thin overhang of chrome returns.
It’s important to stop cutting when you realize your chain is dull. Forcing a dull chain to cut subjects the powerhead, chain, sprocket and guide bar to unnecessary wear and tear. Studies show that dull or improperly maintained saw chains are the true source of most bar-related failures.
Dull chains also wear on operators, causing fatigue, frustration and impaired judgment. This is a safety hazard and another good reason to stop cutting when the chain gets dull.