Saw sharpening

The following article was written by Geoff and is, in his own words "some personal experience and some information plagiarized from a 1930 Disston saw manual".

JOINTING:

To even or flatten the top of the saws teeth along the length of the saw. Similar to jointing the edge of a board with a plane, except using a file. Jointing is done if teeth are uneven or irregular. Setting of the teeth can only be done when teeth are all even. Jointing can be done freehand, or there is a device that is used for holding the file square to the saw, these seem to be quite common at flea markets.

Joint only the highest teeth first, then shape the teeth that have been jointed. Joint the teeth a second time until all teeth have been touched. Be sure to keep the jointing file square to the teeth.

SHAPING:

Shape the teeth only after jointing. Gullets must be of equal depth and the fronts and backs of teeth must be of proper shape. Don't worry about the bevel (cutting edge) at this time, keep the file square (90°) to the saw. If the teeth you are filing are of unequal size, file toward the teeth with the largest tops, that were filed flat by jointing, until you reach the center of the teeth.

The most common tooth angle is 60°. Any steeper than that can cause the saw to suddenly hang up during the thrust, often kinking or breaking the blade. The analogy used to demonstrate this point is a illustration of two knives being dragged across a surface. A knife dragged at a low angle would smoothly flow across the surface while cutting. A knife held perpendicular to the surface would catch, grab and skip.

SETTING:

Alternately setting each tooth of a saw to the left and right provides a kerf that is wider than the thickness of the blade. This provides a clearance that minimizes friction and prevents binding. Setting is not always required after giving the saw a light sharpening, and it is always necessary after jointing and shaping. The teeth of a handsaw should be set before filing the bevel to avoid injury to the cutting edges.

Depth of set should not go, at the most, lower than half the length of the tooth. This is important, if deeper than this there is a chance to spring, crimp, or crack the blade, if it doesn't break the teeth. Hammer and anvil setting requires considerable skill and it not recommended for the amateur.

Setting with a saw set is the recommended method, although many so called saw set are impracticable because they give too deep a set. Be sure you use a better quality pliers type saw set. Too much set causes more work for the sawyer, and the set can be out of proportion to the strength of the blade causing broken teeth. Saw sets are another very common flea market item, be sure to get one with fine adjustments and an undamaged anvil pin. Most people who are selling them, don't seem to know what they are and you can get them from fifty cents to a few dollars.

FILING THE TEETH:

There is much debate over the bevel of the teeth (angle of sharpened edge). In filling saws for cross cutting, the file is held at an angle, and, therefore the teeth are sharpened on an angle or bevel. This angle is usually 45° for cross cutting saws and none to little for rip saws. Some people will sharpen a saw for hardwood with the back of the tooth at a lessor angle than the front of the tooth, or other angles for wet wood, dry wood, etc.

The bevel angle is very important in that it also affects the final bevel of the tooth's point. To much bevel will cause the point to score deeply into the wood without being able to crumble out the waste. This causes the saw to act more like a rasp. Picture sawing with a blade sharpened to a knife edge, verses the normal chisel like edge.

It is best to copy the original bevel pattern if possible, close to the handle where there is minimal wear. If the bevel angle is questionable, keep with the standard 45°, on the front and back of each tooth.

A saw vise or clamp should be used during filing, preferably a strong one to prevent chattering. Top of vise should be in line with operators elbows and 1/8 inch below the bottom of the teeth. Any lower will cause chatter and/or screech, which will quickly dull the file. Again, saw vices seem to be very common and inexpensive at flea markets.

A Disston "Special Extra Slim Blunt Saw File" is recommended, they are sized by length. (New Disston saw files are sold in my local in Ace Hardware store). The Following chart indicates which length of file to use. Also, some file manufactures grade files as slim, x slim, xx slim, etc., they normally have a chart on the bubble pack to match the file to the saws points:

Note: Point is number of teeth per inch.

5 and 5-1/2 point cross-cut teeth, 7 inch.
6, 7, 8, and 9 point cross-cut teeth, 6 inch.
10 and 11 point cross-cut teeth, 5 inch.
4-1/2, 5, 5-1/2, and 6 point rip, 7 inch.
4 point and coarser, 6 inch taper files.

FOR SHARPENING CROSS CUT SAWS:

A light jointing is done first, for use as a guide. Start with saw handle on your right, and stand just to the left of the saw's point, or toe. Find the first tooth that is set towards you and place the file in the gullet to the left of that tooth, at a right angle. Then, swing the file to the left, about 45° or until the file finds it's own bearing. Be sure it is well into the gullet.

The file will cut on the push stroke cutting the tooth on the left and right at the same time. With the file held level, file until you cut away half of the flat top made during the light jointing. File every other tooth until you reach the handle, completing that side.

For the other side, reverse this process with the handle on your left and standing to the right. File every other tooth that was skipped before. File until you cut away the other half of the flat top made on the teeth as a guide, and the teeth are sharpened to a point.

FOR SHARPENING RIP SAWS:

With one exception, this method is exactly the same as that given for cross cut saws. That exception is that the rip saws are filed with the file held straight across the saw at a right angle to the blade. No bevel is needed, although some people prefer to file a slight bevel in rip saws.

SAW CARE:

Saws can be hanged up to minimize damage to the cutting edge. Saws kept in tool boxes should have some sort of edge protection. I have seen people use slit rubber hoses or a piece of kerfed wood held on with rubber bands. Plastic file folder binding strips can also make good edge protectors.

Rub down the saw with oil after use to prevent rust, which causes much friction. Accordingly, sperm oil is the best, and I don't mean sperm oil from a master baiter. These days you will have to find something else to use like a spray on wax. For reasons not explained in this post, avoid the use of silicon spray in your shop.

As an interesting foot note, those sought after brass backed dovetail saws were brass plated, starting at least in 1930. The most expensive dovetail saw was $2.30. In those days you would have to shell out a whooping $10.65 for the top of the line, 6½' two man timber saw.

Geoff Mason

gmason@tcf.com

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