Introduction

• prematurely wears the bar, sprocket, and motor
• cuts slowly and unevenly
• runs roughly
• requires the operator to apply pressure
• leaves a crooked kerf
• produces embarrassingly small wood chips
• overheats
• the chain (and can dangerously loosen it)
• the bar (and can ruin its temper)
• the wood being cut (to the point of burning it)
• increases the risk of kickback and chain breakage
• wastes fuel

• the instruction manual for the brand and model of saw you use
• the information sheet that comes with a new chain of the type being sharpened
• Stihl’s “Sharp Advice for Chain Saw Owners”

To protect your carefully sharpened chain, consider using a Pack Shack bar cover, with a plastic insert (the removable piece that comes with a plastic saw case) pressed inside it to keep the chain from snagging the nylon (figure 1).

To protect your files, store them separately or wrap them so they don’t bump together, and regularly brush them clean of metal shavings.

To protect your hands, always wear gloves while sharpening and be particularly careful when grasping the chain to move it along the bar. (You can also use a file to move the chain.)

Tools

• bench vise, preferably with soft jaws
• drill with wire wheel attachment
• Stihl sharpening kit for the type of chain being sharpened (figure 2)
• file holder with round file
• flat file
• filing gauge (incorporates depth gauge tool and bar-groove cleaner)
• engineer’s protractor
• vernier caliper
• black marker
• file card or stiff brush
• bar-rail edge sharpener

Setup

With the bar and chain attached to the motor, the chain brake released, and the chain snugly tensioned, clamp the middle of the bar in a vise (figure 3), with the clamping point well away from the bar rails. The chain should be just loose enough to be moved around the bar by hand, i.e., tight enough to prevent the cutters from tilting under the file.

Filing the Cutters

Filing Angle

The Stihl file holder provides a convenient, inexpensive, and quick way to achieve a consistent filing angle on the top plate cutting edges. If you have the sharpening kit that matches the particular chain being filed, you will automatically have the correct diameter of round file, as well as the proper filing angle line stamped on top of the holder.

By keeping this line parallel to the bar as you file (figure 5)—and the file holder itself parallel to the floor (figure 6)—you will also be keeping the file parallel to the service marking stamped on the tops of the cutters (figure 7) and thereby achieving the correct filing angle.

Side Angle Plate

The profile of the side plate cutting edge created by the round file determines the side plate angle (60° for the sample chain). Although this angle would be nearly impossible to maintain if filing freehand because the depth of the file is hard to control, the Stihl file holder guarantees that the angle will be accurate and that the profile created by the file will match that of the service marking stamped on the side plate (figure 10)—provided only that the holder slides on the top plate of each cutter and the adjacent depth gauge. The file holder actually yields more accurate side plate angles than some expensive, complicated jigs.

If you wish, you can use an engineer’s protractor (figure 11) or the sighting edge of a Stihl filing gauge (figure 12) to confirm that your side plate angle matches that specified for your chain. (Note that, unlike the rake angles on hand tools, smaller side plate angles mean sharper edges.)

If you are having trouble achieving a high enough side plate angle or a profile that matches that of the stamped service marking, you might experiment with using a file 1/64" larger than recommended.

Cutter Length

Measure the length of all cutters with a vernier caliper (figure 13) to find the shortest one, which is called the master cutter, and mark its top with a black marker (figure 14). If one or two cutters are significantly shorter than the others, perhaps from being damaged, leave them alone and designate the next shortest cutter as the master. Otherwise, you’ll end up removing lots of metal from the undamaged cutters.

After lightly filing the master cutter, measure its length to determine the target length of all the cutters. (When measuring with a vernier caliper, make sure its handle is level and parallel to the bar.) Note that cutters can eventually be filed all the way back to their stamped service markings, although doing so reduces the saw kerf by about 10% relative to that of a new chain because of the cutters’ side-relief angle. The cutters on the sample chain start out 10mm long and can eventually be filed down to 3mm long (the only metric dimension on Stihl chains). Note also the wear guide stamped along the full bottom of each cutter (figure 15); don’t let the bottom of any cutter wear past it.

Filing Procedure

While maintaining the correct filing and side plate angles, file all the cutters on one side of the saw (i.e., half the total number of the cutters) down to the target length. File in one direction only, away from you and toward the outside of the cutters (figure 16).

When you are finished with the half of the cutters facing one direction, reverse the saw in the vise and file the remaining cutters, again filing toward the outside of the cutters (figure 17).

Periodically rotate, brush off, and check the tightness of the file (figure 18). Regularly confirm the filing angle, side plate angle, and cutter length.

Lowering the Depth Gauges

Geometry

Each time you file the cutters, you automatically lower them relative to the depth gauges and, equivalently, raise the depth gauges relative to the cutters. Because the cutters on the sample chain have a 6° top-relief angle, filing them back a given amount reduces their depth by about one tenth (= sin 6°) of that amount. Even a single filing of the cutters after a hard day’s use will leave them perhaps 0.010" shorter and will effectively lower them—and thereby raise the depth gauges relative to them—by a noticeable 0.001".

Because trail workers typically cut several types of wood on a given day, they should err on the side of high depth gauges to avoid rough running and kickback in hardwood (although depth gauges that are too low for hardwood by as much as 0.008" will cut green, unfrozen softwood optimally). Depth gauges should be set for the hardest wood to be cut, a setting that for the sample chain happens to be the one found on new chains of that type and the one recommended in the information sheet that accompanies them, i.e., 0.025".

Flat Filing

Adjusting depth gauges is easy—and accurate to better than 0.001"—if you use the depth gauge tool on the Stihl filing gauge that matches your chain. With the bar still in the vise, set the tool

• flat on top of the cutters
• square with the cutters
• on a level part of the bar near the motor
• with the slotted end of the tool facing away from the motor
• with a depth gauge centered in and butted up against the end of the slot (figure 20)

Use a flat file to remove the tip of the depth gauge that protrudes above the slot in the depth gauge tool (figure 21), filing all the depth gauges on one side of the saw before reversing the saw and filing the remaining half of the depth gauges. File in one direction only, away from you and in the direction of the slight bend in the depth gauges. The file will start to slide smoothly over the hardened flat on the depth gauge tool as soon as a gauge has been lowered the correct amount.

Angled Filing

Each depth gauge will now have a shiny flat-filed top surface parallel to the tops of the bar rails. The next step is to re-file these surfaces at a slight angle to the bar rails so that the new top surface of each gauge slopes up toward the business end of the cutter immediately behind it, i.e., toward the motor. This slight slope will parallel the stamped service markings on the sides of the depth gauges (figure 22). To preserve the depth setting established in the previous step, it is important to leave intact a tiny portion of the flat-filed surface at the top of the new sloping surface on the motor side of each gauge.

Dressing the Bar Rails

Even with normal use, the rails of a chainsaw bar will mushroom noticeably and clog with oily gunk after only a couple of hours of use. Because evenly filed, parallel, deburred, and clean bar rails—along with a clean, well-lubricated chain—are essential to straight, effortless cuts, it is important after filing a chain to remove the bar, dress the rails, and clean out the bar groove and oiler holes.

After noting the orientation of the bar, remove it from the motor and clamp the bare bar in the vise (figure 25). While the bar is off, check the sprocket for wear (figure 26), flipping it over or replacing it if worn indentations exceed 0.02" in depth (for the sample chain). If the sprocket needs replacing, it is best to replace the chain at the same time, so a worn chain doesn’t prematurely wear a new sprocket. Because, on average, one bar will last as long as two sprockets and four chains, a prudent plan is to use two chains in rotation, automatically replace the sprocket when they’re worn out, and have the bar checked by a professional when it’s time to replace the second sprocket.

Using a bar-rail edge sharpener (figure 27), smooth the edges of both rails, filing in one direction only and taking particular care at the ends of the bar to keep the file parallel to the bar and to remove any mushrooming (which you can feel with your finger). Flip the bar upside down in the vise and dress the rails on the opposite side.

The easiest way to “sharpen” a chain in the field is to replace it with the spare chain you should be carrying anyway. Always carry a sharpening kit also, in case either chain needs a quick touch-up.

Resources