| Introduction |
|
| The Jig | |
| Saw Setting | |
| Saw Filing | |
| Some Theoretical Issues | |
| Sloping Gullets | |
| Copyright (c) 2002-11, Brent Beach |
Some of the time you are filing a saw for a specific purpose so need to select rake, bevel and slope angles appropriate to the wood and the type of sawing you will be doing.
| wood type | rake | bevel | |
|---|---|---|---|
| soft wood | 20d to 25d | 40d to 45d | |
| hard wood | 5d to 10d | 20d to 25d |
He adds a few of his own drawings, but those drawings are impossible.
|
THE CARE, SELECTION AND PROPER FITTING OF HAND SAWS A COMPLETE TREATISE FULLY ILLUSTRATED BY Charles L Johnson SAW EXPERT |
For regular hand saws, he gives at least 8 different filings (10d means 10 degrees):
| Use | Rake | Bevel | Points | |
|---|---|---|---|---|
| Fine Cut-off | 10d | 30d | 10-11-12 | |
| Coarse Cut-off | 15d | 40d | 7- 8- 9 | |
| Buck Saw | 20d | 30d | 5 1/2- 6- 7 | |
| Rip Saw | 3d to 7d | 2d to 5d | 5 1/2- 6- 7 | |
| Heavy Ripping | 3d | 2d | 5-1/2 pt | |
| Light Ripping | 5d | 5d | 6 pt | |
| Long Miter | 6d to 7d | 5d to 10d | 5 1/2- 6- 7 | |
| Short Miter | 10d | 10d to 20d | 7-8-9-10-11-12 |
A Buck Saw is a saw for bucking up fire wood - cut quality not an issue, cut speed more important.
A Long Mitre is a cut angled to the grain, but closer to a rip cut.
A Short Mitre is a cut angled to the grain, but closer to a cross cut.
Johnson got around the problem of people not having protractors by including a number of celluloid protractors with his filing manual. The protractors were marked with the various angles. Although copies of the pamphlet survive, I have not seen a protractor.
Johnson says that the file should be level at all times - without saying it, he denies the possibility of sloped gullets. His pamphlet was written at about the time that the Disston books no longer appeared to be suggesting people use sloped gullets.
I use Johnson's Light Rip angles, but find that his recommended bevels for crosscuts are too big.
His directions for filing cross cut handsaws are contradictory on the topic of slope. In the instructions he says: "With your file aligned with a bevel guide, drop the handle the same number of degrees as the amount of bevel you are using ...". However, in a sidebar on he says: "In practical terms, this is not worth the effort."
His recommendations for filing angles:
| Saw type | Rake | Bevel | Slope | |
|---|---|---|---|---|
| Cross-cut | 15 - 30d | 10 - 20d | 10 - 20d | |
| Rip | 0 | 0 | 0 |
I have found that in my shop, the flats are more visible with the saw handle on the right end of my saw vice. The flats are easier to see on the first pass, since they are wider. It is much more important to be able to see them on the second pass, when you are removing them completely. So, always do the first pass with the saw in the direction in which the flats are harder to see.
Jointing should put a small flat on the top of each tooth. If the teeth are not about the same height, some of the teeth will not get a flat after a light jointing. If there are just a few short teeth, don't worry. They won't do much cutting now, but will eventually. It is not worth it to remove a whole lot of metal here just to get a flat on every tooth. If most of the teeth have no flat, joint a little harder.
Charles Johnson recommends making a special jointing file by removing most of the teeth on one side of a file: "place it on a large true faced carborundum whetstone, and grind one face only, until it is nearly smooth". He recommends jointing every time, but is able to joint very lightly with this almost dull file.
Most saws benefit from a little breasting which produces a roach back or salmon back saw. With the teeth pointing up, the middle of the saw is a little higher than either end. The difference is very small - as little as 1/32". You create this shape during jointing - put a little more pressure when jointing near the saw ends than in the saw middle. The arc shape produces a smoother sawing motion. As well, it compensates for a natural tendency of the teeth to become concave rather than convex. Most sawing is done in the middle of the saw, very little within 6" of either end. So, the middle teeth get dull while the teeth on the end remain sharp. Sharpening only the dull teeth produces a concave tooth line - the opposite of the breasted form that works better. (There is no need to get all the breasting the first time you file a saw. Aim for some breasting over a number of sharpenings.)
After the jointing step, the tips of all of the teeth are their final height.
Most saws I have bought have too much set. They may have been set for wet softwoods and I mostly saw dry hardwoods. A tapered saw requires very little set for use in dry hardwoods. All saws will need more set in wet softwoods. More on setting saw teeth using a drawing from an old Chas. A. Strelinger & Co. catalog.
There is a possibility that even though you have set the teeth well one or two teeth are set slightly wider than the rest. As well, on tapered saws, the blade near the heel is thicker than the blade near the toe. Even if set perfectly, the teeth near the heel will be wider than the teeth near the toe.
The teeth now are all of exactly the right height and width/set - too bad they are all dull.
More on setting the saw teeth.
Assemble the jig with the appropriate slider and file. Make sure the braces are level and the file is parallel to the back dowel. Tighten the braces to the back dowel.
You can do it other ways. You can file with the file tip pointing toward the saw handle, or toward the saw toe. You can work from the handle toward the toe, from the toe toward the handle, or alternate. Make sure your strategy gives you the best possible views of the teeth tips on the second filing, when you have to just remove the jointing flats. Find the filing strategy that works for you, lets you produce the most consistent filing, and stick to it.
Set the rake angle using a second slider.
This sketchup model shows the fully assembled jig with the file resting on the teeth. The slider on the back dowel has the appropriate hole angle to provide the desired tooth bevel. The file is on the saw handle side of the jig.
A second slider with the front face having the desired rake angle is placed on the teeth.
Loosen the screw holding the file dowel. With the slider on the teeth and the file in the gullet, rotate the file dowel so the file has the correct rake angle.
As you move this second slider toward the file you rotate the file so the file face aligns with the slider face. This face of the file will produce the front of the tooth which must then have the same angle as the front of this second slider.
Once the file face aligns with the second slider front, tighten the machine screw, locking the dowel position.
The second orientation of the sketchup model, looking from the other end of the file, shows the file face almost aligned with the front of the second slider. As you adjust the file face by rotating the dowel, you push the second slider toward the file until the file face is flush on the front of the slider.
Hard to explain, easy to do.
As you start each gullet, check both neighbouring gullets. If the gullet you are filing is noticeably bigger/smaller than its neighbours, file away less/more than half of the flat. [When using my jig, take a couple of practice filing motions to make sure you are lined up correctly. If you are not lined up the dowel will jam in the slider. If the dowel does jamb in the slider, let go and the jig will move to the correct position. Take a light grip and slide back and forth a couple of times, then resume filing.]
When you near the toe, the slider will drop off the end of the saw. Flip the back dowel to the other side of the file, reset the file rake angle, continue to the toe. If you move back to a gullet you just filed, you can use that gullet to set the rake angle. Having to reset the rake angle for the last few teeth is a real nuisance - you are down to a few teeth on a part of the saw you don't really use. I do it anyway, so the saw is uniformly sharpened.
Before you start in a gullet, check the size of the flats on either side. If the flat on one tooth is larger than on the other, you will have to file the tooth with the wider flat harder. It is actually quite easy with my jig to work only one side of the gullet. If you do not force the corner of the file into the bottom of the gullet, you can file only the tooth face of interest.
When the flats are almost gone, rotate the file away from the teeth so you can check both teeth to compare the size of the flats. When you are almost done, ease up on the filing pressure a little. The advantage of this jig is that you can move the file away from the teeth to get a good look at the flats, then bring it back with exactly the same file position.
This allows you to perform an experiment on noise and effort depending on whether you are filing with or against the set. I think you will find the difference considerable.
Based on this observation, you might want to try a saw filing system that takes 4 passes along the saw, rather than the usual 2 passes. Given the extra saw handling, the gains in noise and effort would have to be considerable.
Pass 1 - Start at the heel, file in the gullet with the tooth set away on the saw handle side, jig set with the file handle toward the heel, and file just the front of away tooth, removing half of the flat.
Pass 2 - Working from the same side of the saw, from the saw toe, with the file handle pointing away from the saw handle, work back toward the saw handle filing just the back of the teeth done on the first pass (the away facing teeth). Since you are finishing the tooth, on this pass you file to just remove the flat. Now both front and back of the away facing teeth are done.
Pass 3 - Working from the other side of the saw, file handle toward the saw handle, file in the gullet with the away tooth on the saw handle side, file just the fronts of the away facing teeth. On this pass you are removing only half of the flat.
Pass 4 - working back from the toe to the heel, file handle facing the toe, do the back of the teeth facing away from you. On this pass you are finishing this set of teeth, so you file to just remove the flat.
This takes twice the passes, but the filing of each tooth goes much faster and is much quieter - you can easily do it this way without hearing protection. Since you are only filing one tooth at a time, you need only look at that one tip. As well, you put the best possible surface (filing away surface) on both the front and back of each tooth.
So, there are three filing systems to try. If you detect an advantage to any one of them, let me know.
Set the jig up as usual, then without jointing or setting, work from heel to toe just filing the fronts of the teeth. One smooth filing stroke to each tooth. Such a light filing will change the height of each tooth by at most a few thousandths of an inch. Such a small change will not put the saw seriously out of joint.
Changing the filing on a mitre-saw from 15 degree rake and 20 degree bevel to 10 degree rake and 40 degree bevel took me two complete filings to get most of the teeth into the new shape. The first filing was very difficult, as the file kept getting stuck on the edges of the old bevels. Many of the teeth looked pretty ugly after the first complete filing.
On the second filing, the teeth were more uniform, but some tooth backs were still not flat.
Removing set is more difficult than tapping the teeth back with a hammer. After several passes down each side there were still teeth that were uneven. Side filing seems to be required to make the teeth uniform. I suspect that there is a lot of spring back since the teeth are not being hammered against an anvil. Do this before reshaping.