Filing New Saw Teeth

With the construction of the saws completed, all that was left to do was to file in the teeth. Commercial saw manufacturers typically cut the teeth in with a machine, resulting in perfectly spaced teeth. I don’t have this equipment, nor do I wish to invest in it, so I use a file. I think teeth that are hand filed in end up working a little more smoothly anyway due to the minor variation in spacing that results from hand filing in the teeth. The random spacing theoretically reduces harmonic chatter, if only slightly. In my experience using saws in which I’ve filed in the teeth compared to saws I have with machine cut (but hand filed) teeth, I can notice a slight difference, but it is only slight.

I set the tooth spacing by drawing lines with a CAD program and printing it out full scale. I place the piece of paper in the vise with the saw plate and file a small notch at each line. This one happens to be 12 PPI (or 11 TPI).

saw_filing01

Once I’ve filed a notch at each gullet location by making one or two passes with the file, I remove the paper. I then go back and make several more passes at each notch to deepen the gullet and rough shape each tooth. At this point, I’m just trying to get close to the final rake angle so I don’t use a guide to set the angle of the file. In fact, I’m just trying to keep the front of each tooth vertical at this point (i.e. 0 degrees of rake) and I do this by eye. I file just until the flats on top of each tooth disappear or almost disappear and no further. I file the initial notches and shape all the teeth from one side of the saw plate, prior to setting the teeth.

Once all of the teeth have been rough shaped, I set the teeth. I use a plier type saw set for this. I begin at the heel of the saw and work toward the toe setting every other tooth. I’m just trying to set the top 1/3 or so of each tooth, not the entire tooth. If you try to set the entire tooth, you might break them off. Once I’ve reached the toe, I flip the saw around in the vise and set the remaining teeth so that each tooth is alternately set when I’m done. If you make a mistake and set two teeth in a row in the same direction, don’t worry about it. It won’t affect the performance of the saw and it can always be fixed at a future sharpening if needed. Do not try to set a tooth in the opposite direction of it’s original set or you are about gauranteed to break the tooth off.

saw_filing02

After I have set the teeth, I like to joint them lightly with just one or two light passes with a 6″ mil file. I hold the file tight to a block of wood which acts as a fence to keep the file square to the tooth line. This seems counter productive to the initial shaping I just worked so hard to do, but jointing lightly after setting the teeth ensures that each tooth will be the same height after sharpening, even if the set is a little uneven. It also provides a reference flat on top of each tooth to guide my final filing.

saw_filing03

Another aid for doing the final filing of the teeth is to darken the flats from jointing. You can use a permanent marker for this, and I did for years, but the teeth tend to chew up the marker tip pretty quickly so you never really use a marker until the ink is gone. Machinists layout dye is another good option, however, it’s awful messy.

My solution is to use an old planemaker’s trick, a candle. By running the saw teeth back and fourth several times through the flame of a regular old candle, you coat the saw teeth with a thin coat of soot. The dull black soot covers well and provides a good reference for teeth that have been filed and those that have not. You don’t hold the candle in one spot for so long that the saw plate heats up (this could ruin the temper of the steel) rather you keep the candle moving continuously to “paint” on the soot.

saw_filing04

With the teeth coated in soot, I begin the final filing and sharpening of the teeth. Now that the teeth are set, I can’t just file all of the teeth from the same side. I need to file only the teeth that are leaning away from me. I also now use a guide block to guide the angle of the file in order to set the desired rake angle. Here, it’s about 4 degrees.

saw_filing05

The guide block is simply a small scrap of soft wood with a small pilot hole drilled centered on each edge. I then draw a line tangent to the hole at the desired rake angle. The rake angle should lean toward the handle. So in this picture you can see how I’ve noted on the guide block which side the handle needs to be on. The rake angle leans toward the handle from bottom left to top right at an angle of 4 degrees from vertical (the opposite edge of the guide block is a mirror image of this edge). I insert the file into the pilot hole with the right side flat parallel to the rake angle line. All I need to do now is file with the wood block held level and I will maintain the 4 degree rake angle.

Again, I start at the heel and work toward the toe, filing every other tooth (only those leaning away from me). I file straight across (90 degrees) the saw plate because these are rip teeth. I make only one or two passes on each tooth until the flats on top of each tooth are smaller by about half. Be careful because this goes faster than you might think, especially on these smaller teeth. It takes only one or two light strokes of the file.

Here you can see where every other gullet has been filed as noted by the shiny gullet. The candle soot remains on the unfiled teeth.

saw_filing06

Once I reach the toe, I flip the saw around in the vise so that the unfiled teeth, which were leaning toward me before, are now leaning away from me and the saw handle is on the left.

I NOW REVERSE THE GUIDE BLOCK ON THE FILE. The opposite side of the guide block is a mirror image of the first side. It has an arrow pointing to the left where the handle should now be and the rake angle is tangent to the left side of the hole and should lean from the bottom right to the top left at 4 degrees from vertical. The file is inserted with it’s left edge parallel to the rake angle line. This is an extremely important step. If you keep the guide block in the same orientation as before, the rake angle will be all wrong and when you file the teeth you’ll end up filing them into little toothpick points, so make sure you reset the file in the guide block so that the rake angle is correct.

With the guide block on the file switched to its proper orientation and the saw flipped around in the vise, I can now file the remaining teeth. Again, I start from the heel and work toward the toe filing straight across because these are rip teeth. I file only until the flats on top of each tooth disappear and no further, even if the teeth are different sizes (the size isn’t important, the final height is). Once I reach the toe, the filing is complete and the teeth should be very sharp.

I perform one final step prior to using the saw. I like to joint the sides of the teeth to remove the filing burrs and smooth the teeth out some. To do this, I place the saw plate on the edge of my bench and with an oiled hard Arkansas slip stone, I make one pass with light pressure from heel to toe, keeping the stone flat to the side of the saw plate. I then flip the saw over and joint the other side the same way, making only one pass from heel to toe.

saw_filing07

Once I’ve done the side jointing, I’m finished with the sharpening. I use a little turpentine on a rag to clean the remaining soot from the blade and the saw is ready to go back on it’s peg until it’s called on to cut some tenon cheeks.

Here’s a shot of the finished rip teeth. They’re not perfectly spaced, not all exactly the same size and likely not all exactly the same rake angle, however, they don’t need to be perfect and hand filed saws never are. In fact, the imperfections are what make hand filed saws such a pleasure to use. They cut smoothly with no vibration or chatter and seem to glide through the wood.

saw_filing08

If you don’t already sharpen your own hand saws I hope this will encourage you to give it a try. It’s really not that hard to do and if you just take it step by step and go slow it’s very difficult to ruin a saw and near impossible to take it beyond repair. If you make a mistake, it’s a simple task to rejoint the teeth down and start over.

Oh yeah, and the obligatory test cut was smooth, fast and straight. Can’t ask for any more than that ; )!

saw_filing09

Advertisements

3 thoughts on “Filing New Saw Teeth

Comments are closed.