Saw Sharpening

Filing and sotting a saw is considered by some to be a difficult job not to be attempted by the average farmer or farm boy. With some study and practice, however, most boys of high school age who have a reasonable amount of mechanical ability can learn to sharpen saws quite acceptably.

Before attempting to sharpen a saw, one should have clearly in mind the proper shape of the teeth, and it is desirable also to understand the cutting action of a saw.

169. Shape of Saw Teeth.—There are two principal differences in the shape of ripsaw and hand crosscut saw teeth. One difference is in the

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Fig. 149.—A. Hand crosscut saw. D. Ripsaw. Thews are two chief differences in the shape of crosscut and ripsaw teeth:

1. Crosscut saw teeth are beveled; ripsaw teeth have square edges.

2. The front edges of ripsaw teeth are perpendicular to the tooth line, while the front edges of crosscut saw tooth make an angle of about 15 deg. with the perpendicular.

hook or pitch of the teeth. The front edge of a. ripsaw tooth is perpendicular to the tooth line of the saw, while the front edge of a crosscut saw tooth makes an angle of from 12 to lo deg. with the perpendicular (see Fig. 149).

The second chief difference is that the crosscut saw tooth is beveled, while the ripsaw tooth is not. In filing ripsaw teeth, therefore, the file is pushed straight across the blade; and in filing crosscut saw teeth, the file must make an angle with the saw blade to form the bevel. The usual

angle is between 45 and 60 deg. A 45-deg. angle gives a wider bevel and a keener edged tooth, which is desirable for sawing softwood; while a 60-deg. angle gives a narrower bevel and a. blunter tooth that will stay sharp longer in sawing hardwood. The narrower bevel, produced by filing at about 60 deg. to the blade, is usually preferred for general-purpose farm saws.

The front edge and the back edge of a handsaw tooth make an angle of 60 deg. with each other, regardless of whether it is a ripsaw or crosscut saw tooth.

170. Set of Teeth.—It will be noted upon examining a saw that the points of the teeth are bent outward, one tooth in one direction and the next tooth in the opposite direction. This alternate bending of the teeth gives a saw what is called set and causes it to cut a kerf (groove) that is slightly wider than the thickness of the saw blade, thus preventing binding or pinching.

171. Cutting Action of Handsaws.—The ripsaw Is used for cutting wood lengthwise of the grain or fibers. The teeth act like a series of small

Fia. 160.—Cutting action of a ripsaw. The teeth act liko a series of small chisels following each other and cut off the ends of the fibers.

wood chisels following each other, and cut off the ends of the fibers (soe Fig. 150).

The crosscut saw of course is used for cutting across the grain or fibers. It first makes two parallel incisions with the points of the teeth, thus severing the fibers; and then forces out the wood between the incisions in the form of sawdust (see Fig. 151).

172. Steps in Sharpening a Saw.—There are three chief operations or steps in fitting a saw, namely, (1) jointing, (2) setting the teeth, and (3) filing. A fourth operation, that of side dressing or side jointing, may be, but is not generally, performed on farm saws.

Shape Tooth Ripsaw

Fia. 160.—Cutting action of a ripsaw. The teeth act liko a series of small chisels following each other and cut off the ends of the fibers.

173. Jointing.—Jointing is done by running a mill (flat-type) file over the ends of the saw teeth, lengthwise of the saw, using light pressure and keeping the file square with the saw blade. Jointing has a two-fold

How Small Saw Filing

purpose: (1) to make the teeth all the same length and (2) to serve later as a guide to indicate when the teeth are filed enough. Jointing leaves a small flat shiny surface on the point of each tooth. When this surface just disappears in filing, the tooth is sharp and should not be filed further.

How Small Saw Filing

In jointing it is important that the file be kept square with the saw blade. This can be done by grasping the file with both hands, holding it by the edges, thumbs on top and first, fingers underneath (see Fig. 153).

A wooden square-edged block or a special tool may also be used to hold the file in proper position (see Fig. 152). The tooth line should be straight, or curved out slightly in the middle of the saw, giving it a "breast" effect.

The saw should be jointed until there is a small shiny surface on the point of each tooth, except possibly an occasional very short tooth.

If the teeth of a saw are of uniform length, and require but light filing, many experienced mechanics omit jointing. By filing each tooth the same number of strokes, they are able to keep the teeth uniform in length without first jointing them.

Flo. 153.—A saw may be jointed with a file held in the hand» if caro ia used to keep it square with the saw blade.

174. Setting.—After jointing, the saw teeth arc next set, unless they are very uneven in shape and size. In this case, the teeth should be filed to approximately the correct shape and size before setting, and then filed again after setting.

A saw may not need setting every time it is to be filed, particularly if only a light filing is required. A saw can sometimes be filed two or three times before it needs to be reset.

Setting is commonly done by means of a small tool known as a spring saw set. The tool is placed over a tooth, and the grips squeezed together which pushes a small plunger against the end of the tooth, forcing it over against the anvil of the set. In setting the teeth, begin at one end of the saw and set every other tooth, being careful to bend the teeth in the same direction they were originally set. Then reverse the saw and set the remaining teeth.

Flo. 153.—A saw may be jointed with a file held in the hand» if caro ia used to keep it square with the saw blade.

Most saw sets are adjustable, and, when using one with which you are not familiar, it. is best to set a few teeth first, and examine them closely before setting the whole saw. If the teeth are not set enough, or too much, the tool should be adjusted accordingly.

Fig. 154.—Setting a saw with a spring saw set. Half the teeth are &ei from one side; then the saw ia reversed in the clamp and the other half set from the other side.

175. Depth and Amount of Set.—Only the point of the tooth, or from one-third to one-half the length of the tooth, should be bent in setting. If the depth of set is too much, some teeth may be broken out, or the blade may be kinked or cracked.

The amount of set a saw should have depends upon the kind of wood to be sawed and upon the thickness of the saw blade above the teeth. The better saws are ground thinner above the teeth and therefore require very little set. Green or wet wood will require more set than dry, well-seasoned wood; and softwoods, more than hardwoods. For average work bending the teeth out Hoo in- should be ample. Too much set causes the saw to cut too wide a kerf, resulting in poorer control of the saw and extra work to push it. Too little set causes pinching or binding of the blade in the kerf.

176. Filing a Hand Crosscut Saw. Placing Saw in Clamp.—The saw should be held securely in a saw vise or clamp with the teeth projecting between and 24 in. above the jaws—just enough for the file to clear the jaws easily. If the teeth project too far above the clamp, the saw will chatter and the file will screech. A clamp made of two one by fours and used in an ordinary vise is quite satisfactory.

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Fig. 154.—Setting a saw with a spring saw set. Half the teeth are &ei from one side; then the saw ia reversed in the clamp and the other half set from the other side.

For best work the top of the saw clamp should be at about the height of the arm pits or possibly ail inch or t wo lower. One must be constantly on guard while filing to maintain the desired shape of teeth, and this can best be done when the sides of the teeth are easily seen; hence, the rather high position of the saw while filing it.

Work in a Good Light.—In order to avoid eyestrain and to insure a good job of filing, good light is absolutely essential. It is usually best to work in front of a window where the light will shine on the teeth and it will be easy to see the reflections from the small shiny surfaces left by jointing.

Kinds of Files lo Use.—The kind and size of file to use depends upon the size of the saw teeth and the preference of the mechanic. In general, 6-in. slim taper saw files are recommended for saws with seven to nine

points per inch and 7-in. slim taper files for saws with five to six points per inch. Some mechanics prefer blunt files instead of tapered ones.

Using the File.—The file handle should be held firmly in the right hand (assuming the workman is right-handed), and the tip of the file held lightly between the thumb and first finger of the left hand. The file should cut on the forward stroke only, and should be lifted slightly on Vie return stroke. Slow, even, full-length strokes should be used. A file should not be allowed to slide along without cutting. If the file is sharp, a slower stroke with a little more pressure will usually remedy the trouble. If it is dull, it should be discarded and a new file used.

First Position.—Place the saw in the vise with the handle to the right. Start at the end of the saw (see Fig. 156.4). Place the file in the gullet (V-notch between two teeth) to the left of the first tooth that is bent out toward you. Place the file across the saw blade at an angle of about 60 deg. with the file pointing toward the handle of the saw. Press the file firmly into the gullet and let it find its own bearing against the teeth. Do not point the file upward nor downward, but keep it level. (If the file tends to screech it may be pointed upward very slightly.) Push the file forward, cutting the back edge of one tooth and the front edge of the adjacent one with the same stroke. Lift the file slightly on the return stroke, and continue filing until about half of the fiat shiny surfaces made by jointing are filed away.

Then move the file two gullets to the right (towards the handle) and file in a similar manner. Continue filing in every other gullet until you reach the handle.

Second Position.—Turn the saw around in the clamp and place the file in the gullet to the right of the first tooth that is set out toward you (see Fig. 156#). With the file pointing toward the handle of the saw and making an angle of about 60 deg. with the saw blade, push it forward,

Fio. 156.—The two positions for filing a hand crosscut saw.

A. First position.—Begin at the tip of the saw and work toward the handle. Hold tho file at an angle of about 60 dog. to the saw blade and be sure that the file cuts the front edge of each tooth at an angle of about 15 deg. from the vertical.

B. Second porilion.—After half the teeth are filed, turn the saw around in the clamp and file the other half from the other side.

cutting away the remaining half of the flat, shiny surfaces made by jointing. In a similar manner, file in every second gullet until you reach the handle of the saw.

Final Touching Up.—After filing a saw it should be carefully examined to see if any blunt tooth points remain from jointing. If they do, then these teeth should be filed until the flat points just disappear. Some mechanics prefer to simply repeat the filing process described above, filing in first position and in second position, but filing only those teeth that still have flat points.

Keeping Proper Shape and Angle of Teeth.—It is very important that the front edges of the teeth be filed to a. pitch of 12 to 15 deg. from the vertical (see Fig. 14&4). It is important also that the file be held at a uniform angle of about 60 deg. with the saw blade in order to produce the proper bevel. By placing the file in a gullet between two properly filed teeth and letting it seek its own position, the desired angles for filing can be determined. The beginner must be constantly on guard, however, to keep this position after it is determined.

Filing the teeth in pairs with a short broad tooth next to a long slim one is a common trouble among beginners and is the result of not maintaining the proper slope of 12 to 15 deg. on the front of each tooth. To correct the trouble, therefore, first be sure that the file is held so as to give the proper angle of 12 to 15 deg. on the front of the teeth, and then press the file firmly against the broad tooth and lightly, if at all, against the narrow one, as it is pushed through the gullet between them.

177. Filing a Ripsaw.—The same general procedure is used for filing ripsaws as for hand crosscut saws. There are two points of difference, however, that need to be kept in mind:

1. The front edges of the teeth are perpendicular to the tooth line instead of at an angle of 12 to 15 deg. to the perpendicular.

2. The edges of the teeth are not bc%'d©d but are square with the saw blade (see Fig. 149).

Except for the difference in angles of filing required by these two differences, a ripsaw is filed exactly the same as a crosscut saw.

178. Side Dressing or Jointing.—A saw is side dressed or side jointed by laying it on a flat board or bench and rubbing the saw lightly on the sides with the edge of an oilstone or with a fine file. The object is to smooth off any rough edges left from filing and to even up the set in the teeth. Side dressing is usually not necessary for general sawing.

If after trying a saw it is found to be set unevenly and tends to run to one side of the line, it may be side dressed on the side that leads away from the line. Side dressing may also be used to reduce the amount of set in case the saw cuts too wide a kerf.

Points on Sharpening Handsaws

1. Always work in a good light so that the points of the teeth may be easily seen.

2. Set only the points of the teeth—not more than one-third to one-half the length of the teeth.

3. The top of the saw clamp should be at about the height of the arm pits.

4. Allow the teeth to project above the saw clamp from % to in. just, enough for the file to clear the jaws of the clamp.

5. File on the forward stroke only. Lift the file slightly on the back stroke.

6. Use long, slow, even strokes. K the teeth are reasonably uniform in shape and size, each tooth will require about the same number of strokes.

7. Just barely file away the flat shiny surfaces on the points of the teeth left by jointing.

8. Have no slope to the front edges of ripsaw teeth. Make them perpendicular to the line of the teeth.

9. Slope the front edges of crosscut saw teeth 12 to 15 dog. from a perpendicular to the line of teeth.

10. In filing a crosscut saw, point the file toward the handle of the saw, keeping the angle between the file and the saw blade at about 60 deg.

11. In filing a ripsaw, file straight across, keeping the file at right angles to the saw blade.

12. Do not point the file upward or downward, but keep it level.

13. If the teeth are uneven in size, first be sure the file is held to give the proper slope on the front edge of the teeth, and then press hard against the big ones, and lightly, or not at all, against the small ones.

179. Selecting Saws for the Farm Shop.—Every farm should have a crosscut, hand saw. A saw 26 in. long and with 8 points per inch is usually recommended for general work. A coarser saw with 6 or 7 points per inch will saw somewhat faster but will leave rougher edges; and a finer

Fia. 157.—The size of teeth is designated by the number of points per inch. There is always one more point than there are teeth per inch. For average farm shopwork, a hand crosscut Raw with 8 points per inch and a ripsaw with 6, 6H. or 6 points per inch will be Quito satisfactory.

saw with 10 or 11 points per inch will do. smoother work but will saw slower.

Where it can be afforded, a ripsaw should also be included in the shop tools. A ripsaw 26 or 28 in. long and with 5, 5^, or 6 points per inch is usually preferred.

There is always one more point per inch than complete teeth per inch. An 8-point saw, for example, really has but seven teeth per inch (see Fig. 157). This is because of the custom of counting the first and last-points in an inch.

180. Cleaning Rusty Saws.—Saws should be oiled occasionally with light oil to prevent rusting. If a saw has bccoinc rusty, however, it may be cleaned by rubbing with pumice stone and water, or pumice stone and oil. Sand paper or emery paper would scratch a saw blade arid is, therefore, not recommended. After cleaning, a saw should be thoroughly dried and oiled.

181. Sharpening Bucksaws and Pruning Saws.—The same general principles used in setting and filing crosscut handsaws apply in setting points per fncD-4^ teeth

One inch points per fncD-4^ teeth

Crosscuf.saw

Rip saw and filing bucksaws and pruning saws. The shape and angles of the teeth of bucksaws and pruning saws are different from handsaws, however, and therefore the file must be held differently when filing them. The proper shape of teeth can be determined by looking at some of the teeth near the ends of the saw that have not been used a great deal. Holding the file firmly between two of these teeth near the end of the blade will give the correct angles for filing.

Fig. 168.—A rusty saw may be easily clcaned by rubbing with pumice stone and water, after which it- should be wiped dry and oiled.

182. Sharpening Crosscut Timber or Log Saws.—To sharpen timber or log saws, one should have a combination jointer and raker gage, and a saw set for such saws. It Is possible, however, to set a timber saw with a hammer and setting block. A mill (flat-type) file about 8 in. long is used to file the teeth.

The operations in fitting a timber saw are (1) jointing, (2) filing down the raker teeth, (3) setting the cutting teeth, and (4) filing the teeth.

Fig. 159.—How a crosscut log saw works. The right and left cutting teeth make incisions and the raker teeth cut out the wood between incisions.

Jointing.—To joint a timber or log saw, place a file in the jointing tool and file down the teeth until the shortest of the cutting teeth is reached. If the saw is in fair shape, very light jointing is all that is necessary. It is very difficult to hold a file in the hands and joint the teeth of a timber saw because the teeth are too long.

Fig. 168.—A rusty saw may be easily clcaned by rubbing with pumice stone and water, after which it- should be wiped dry and oiled.

Fig. 159.—How a crosscut log saw works. The right and left cutting teeth make incisions and the raker teeth cut out the wood between incisions.

Fiq. 161—4. A »aw tool in place ready for filing down the raker*. Rakers should be filed

to K2 in- shorter than other teeth. B. Filing down the rakors.

Filing Down the Rakers.—The rakers, or those teeth which shave off and carry out the wood between the two parallel incisions made by the cutting teeth, should be a little shorter than the cutting teeth, the exact amount varying with the kind of wood to be sawed. In general they should be about in. shorter for hardwoods, and about 142 in. shorter for softwoods. To file down the rakers the raker gage is placed on the saw, and the points of the rakers filed down even with the gage.

Setting the Teeth.—The teeth may be set with a hammer and setting block or with a spring saw set. Many prefer the spring set. Not more than in. on the end of a tooth should be bent. A homemade setting block can easily be made by filing a corner of a piece of iron as

Fig. 'l63.—The gullets of the raker shown in Fig. 162. tenth should bo filed ao that the square Filing the Teeth.—The rakers are end of the file will fit. Care should bo i . . . e .. __1 „ . i taken not to file the rakers too short.. hl<xl on the inside of ttie end notch with a flat file. The angle at the center of the notch should be about a right angle. Care should be exercised not to file the teeth shorter than the length to which they were jointed. It is a good practice to file half of the rakers from one side of the saw, and the other half from the other side.

Fia. 164.—Filing -the cutting teeth of a crosscut, log saw.

The cutting teeth are filed much in the same manner as the teeth of a crosscut handsaw. Half of the teeth are filed from one side and half from the other. The angle of the points and the width of the bevel on the cutting teeth depend upon the kind of wood to be sawed. For soft woods, a long point with a wide bevel is recommended, and for hard woods, or knotty or frozen wood, a blunter point with narrower bevel is recommended.

Gumming a Saw.—After several filings, the gullets between the teeth of a timber saw become so shallow that they can not well hold all the sawdust made by the teeth. Consequently the sawdust binds against the sides of the saw kerf and makes the saw pull hard. The saw should then be gummed, that is, the gullets should be filed or ground deeper. It is a very slow, tedious job to gum a saw with a file. The best method is to use a special thin grinding wheel made for this purpose. A special stand or work rest can be made in front of the grinder to support, the saw while it is being gummed. It is best not to do all the gumming in a gullet at one time, but to grind a little in one gullet and then proceed to the next, going over the saw three or four times to complete the job. This avoids overheating the saw and drawing the temper.

183. Sharpening Circular Saws.—In sharpening a circular saw, the same general operations are performed as in fitting a handsaw or a timber saw. The operations are (1) jointing or truing, (2) gumming, if needed, (3) setting, and (4) filing. Not all the operations need be done every time the saw is fitted.

Jointing a Circular Saw.—A circular saw is jointed to make it truly circular, or to make the tooth points all the same distance from the center of the saw. Jointing is usually best done by leaving the saw mounted on its own shaft and turning it slowly backward by hand while holding a file firmly yet lightly against the ends of the teeth. An easy method of holding the file in proper position is to adjust the saw so that the teeth barely project through the slot in the saw table, and then hold the file fiat on the table over the slot.

Gumming a Circular Saw.—A circular saw may be gummed in the same manner as a timber saw. It may be done with a round file or a flat file with a round edge; but a much easier way is to use a special saw-gumming wheel. Circular saws with certain kinds of teeth, such as fine-toothed crosscut saws, do not require gumming.

Setting a Circular Saw.—The teeth of a circular saw may be set with a hammer and setting block or with a large spring saw set. The amount and depth of set required will depend upon the kind of a saw, whether it is a ripsaw, a cutoff saw, a cordwood saw, etc., and upon the kind of wood to be sawed. If, after fitting a saw, it is found to bind in the saw kerf, it is a simple matter to give it a little more set.

Filing a Circular Saw.—The kind of a file to use in filing a circular saw will depend upon the shape and size of teeth. For a crosscut saw, usually a three-cornered file about 8 in. long is used. For a ripsaw or a cordwood saw, a mill (flat-type) file about 8 or 10 in. long is used.

In filing a circular saw, care must be taken to preserve the original angle of bevel and the original pitch of the teeth. The proper position for the file can be determined by pressing the file into a gullet, or against the side of a properly filed tooth, and allowing it to "seat" against the tooth.

Questions

169. What are the two main differences in shape of crosscut and ripsaw teeth?

170. (a) What is set in a saw? (fe) Why is it needed?

171. (a) Just how do the teeth of a ripsaw act in ripping a board? (6) Describe the action of crosscut .saw teeth in sawing a board.

172. What are the steps performed in sharpening a handsaw?

173. (a) What is meant by "jointing" a saw? (6) What are the two main purposes of jointing? (c) What are the important points to be observed in jointing a saw? (d) Under what conditions might the process of jointing be omitted?

174. (a) Should a saw be set every time it is filed? (6) Just how does a saw set bend the teeth? (c) Explain and be able to demonstrate just how a saw is set.

176. (a) What is meant by "depth of set"? (6) In general how much should the depth of set be? (e) What is meant by "amount of set"? (d) What kinds of wood require the most set? (e) For average work, how much should the teeth be bent out in setting?

176- (a) In placing a saw in a clamp preparatory to filing, how far should the teeth project above the jaws of the clamp? (b) What is the best height for the clamp or vise? (c) How should the clamp be placed with respect to a window or lamp to give best light? (<d) What kinds and sizes of files are best for filing handsaws? (e) How should the file be held, and what kind of strokes should be made? (J) What is the first position for filing a saw? (g) Does the file cut on both the forward and on the return stroke? (A) Should the file cut on only one tooth at a time? ($) How can the workman know when a tooth is filed enough and yet, not too much? (j) What is the second position for filing a handsaw? (k) What is the cause of getting the teeth filed in pairs with a short broad tooth next to a long slim one?

177. In what respects is the process of filing a ripsaw different from filing a crosscut saw?

178. (a) What is meant by "side jointing" a saw? (b) How is it done? (c) What is the purpose of side jointing?

179. (a) What kind and siae of handsaw' would you recommend for the farm shop? (b) What kind and size of ripsaw would you recommend? (c) What is meant by an "8-point" saw?

180. (a) How may a saw be kept from rusting? (6) How may rust be cleaned from a saw?

181. (a) In what, ways are pruning saws and bucksaws sharpened differently from handsaws? (i>) How may the proper shapes and filing angles usually be determined for such saws?

182. (a) What tools are needed for sharpening log saws? (fc) What are the step« or operations in sharpening and fitting such saws? (c) What different kinds of teeth does such a saw have, and just what is the purpose of each? (d) How much shorter should the rakers be than the other teeth? (e) How are the teeth of a log saw set? (/) What is the proper shape of the notch on the end of the rakers? {g) What kind of file is used in sharpening a log saw? (h) What is meant by "gumming" a saw? (t) How is a saw gummed? (j) What difficulties are likely to be encountered if a saw is not gummed when it needs it? (k) What particular precaution should be observed when gumming a saw with a grinding wheel?

188. (a) What are the operations in sharpening a circular saw? (6) How may the teeth of a circular saw be jointed? (c) How may they be set?

References

Hjoeth: "Basic Woodworking Processes/'

Brown and Tustisox: "Instructional Units in Hand Woodwork." Boss, Dent, and White: "Mechanical Training." Rokhi,: "Fitting Farm Tools."

Cornell Extension Buli. 91, Fitting the Farm Saws.

Educational chart« and pamphlets, Stanley Tool Works. New Britain, Conn.; Henry Diss ton and Sons, Philadelphia, Pa.; Simonds Saw and Steel Company, Fitch' burg, Mass.; E. C. Atkins and Company, Indianapolis, Ind.

Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

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