Crosscut Saw Manual

Filing the Saw, continued

Raker Fitting

The raker teeth remove shavings that the cutter teeth have severed from the wood. For a saw to operate efficiently, the raker must remove all the wood severed by the cutter teeth, but no more. If too little wood is removed (too short a raker), energy will be wasted because of unnecessary friction between the cutter teeth and unremoved wood. If too much wood is removed (rakers too long), it is necessary for the raker to break the uncut fibers along the edge of the chip, resulting in wasted energy and a "whiskered" shaving.

Shaving
Image comparing a good shaving to a whiskered one.

Because the cutting teeth exert pressure on the wood as they cut, a certain thickness of wood is compressed and springs back after the teeth pass over. As a result, fibers are not severed quite as deeply as the teeth penetrate. Consequently, the rakers following the cutter teeth must be shorter by the amount that the wood springs back, so no unsevered wood is removed. The amount of springback varies with wood type, moisture content, saw weight, and cutter tooth shape. Optimum raker depth depends on all these factors.

How a cutter tooth cuts
Image showing how a cutter tooth cuts.

Optimum depth is obtained by experiment, but figures vary from 0.008 inch for hard or dry wood to 0.030 inch for soft, springy wood; 0.012 inch is a good average figure to begin with.

The depth of the rakers below the cutter teeth is determined by using a tool called a raker gauge or raker depth gauge.

The raker depth gauge is generally part of a combination saw filing tool of which numerous varieties were manufactured. The essential feature of all of them is a hardened steel filing plate with a slot cut in it a little wider than the thickness of a saw and a little longer than the distance between the two tips on a raker. This is held on a frame so that when the gauge is placed over the raker, the top of the filing plate is the same level as the desired raker depth. The raker tips are cut to the level of the plate with a file. The height of the filing plate is adjustable.

Raker Gauges

Photo of a Morin raker gauge.
Morin raker gauge

Photo of a Simonds precision saw tool.
Simonds precision saw tool

Photo of an Anderson raker gauge.
Anderson raker gauge

Adjustment of the depth gauge is straightforward. With the simpler gauges, such as the common Morin gauge, two screws hold the filing plate to the frame, and the adjustment is made by putting pieces of paper between the frame and the filing plate. The Simonds precision saw tool adjusts by sliding the filing plate up and down two ramps. A scale on the side of one of the ramps indicates the depth of the top of the filing plate. Each division of the scale corresponds to 0.004-inch difference in the height of the filing plate. A notch opposite the scale on the filing plate indicates the desired raker depth. The Anderson gauge adjusts by moving the plate up and down with a screw. Only minor adjustments should be made using the screw, because large deviations could break the brittle filing plate. Paper between the filing plate and the tool frame can be used for large adjustments. The Anderson gauge is the only known gauge with a sloped filing plate. Instead of filing the raker tip flat, it establishes a 15-degree clearance angle.

One way of checking the setting of a raker gauge is to file a raker using the gauge. Place a straightedge between the two cutter teeth on each side of the filed raker and measure the relative height with a feeler gauge placed between the raker and straightedge.

Filing raker teeth
Image showing a file in a filing raker tooth.

There are two basic ways a raker can be shaped before it is filed to its proper depth using the raker depth gauge. These are known as straight (plain) and swaged rakers. There are advantages and disadvantages to each method. The straight raker is by far the easier to file, but it results in a relatively "slow" running saw. The swaged raker is considerably more difficult to shape, but the results are a superior running saw. The reason for the difference is apparent when one remembers that the raker acts like a chisel to remove the shaving. Much less energy is required to remove wood from a board if a chisel is held at a low angle to the board than if it is held vertically. Swaging results in a raker tip that is similar to a chisel held at a low angle to the wood.

Fitting Straight Rakers

The teeth of a saw are formed by punching, so the gullets of most saws are rough. With a 7- or 8-inch, slim-taper file, dress (smooth) the outside face of the rakers from the raker tip to the bottom of the sawdust gullet. Make sure the file is held square with the saw. This will provide clean, sound metal for the cutting edge of the raker, cause less friction between the outside face and the shaving, and aid shaving removal.

Next, file the raker to the proper depth. Place the properly adjusted raker gauge on the saw so the raker fits in the slot in the filing plate. Hold the gauge so it rests firmly against the tops of the cutter teeth as well as the side of the saw. Run a file across the raker tips until they are even with the top of the filing plate. Once the raker tips have been filed, the rakers must be sharpened. With a 7- or 8-inch slim-taper file, shape the raker gullet to the approximate shape (shown next), rounding the gullet out to the tip until the flat spot on the top almost disappears. If the tip is overfiled, it changes the raker depth. If not filed enough, the flat spot acts like a "sled runner" and does not allow the edge to work properly.

Shaping a raker tooth (straight raker)
Image showing the angle needed for shaping a straight raker tooth.

If you're using an Anderson-type gauge, this step is not critical. The clearance angle has been established and a good-sized "flat" spot can be left. Make sure the end of the filing slot in the Anderson gauge is held firmly against the tip of the raker. Otherwise, the raker tip will be filed too low.