Jointing
Careful sharpening can help avoid the need for jointing the teeth but when the teeth are of an uneven height, the first step in saw sharpening is jointing them even. It is extremely easy to joint the teeth with nothing more than a flat file, but there are scads of saw jointer
file holders on the market. Use an 8″ or 10″ smooth-cut flat file and just run the file lightly along the entire length in one pass.
With your lamp adjusted properly you should be able to see a small, shiny flat on the top of each tooth. Different tooth heights will make different sizes of flats. If there are any teeth without a flat, take another jointing pass. If there are any teeth missing or much shorter than the others, don’t try to joint all the others to match unless there are many missing in a row (in which case you will have to joint all the way down to them and reshape all the teeth to match). Just leave them for now and subsequent sharpenings will eventually catch up to them as the other teeth are jointed and shaped over time.
Shaping
Skip this step if the teeth on your saw are uniform, properly shaped already and simply in need of sharpening. However, if the teeth are in need of reshaping, get the right file, the prepared alignment guide — that scrap of wood with the hole in it — and clamp the saw tightly in the vise, with the teeth just clear of the vise jaws. Start at the handle end and work toward the toe of the blade. Study the flats on the tops of the teeth that were made when you jointed the saw. The goal is to reshape each tooth, with the proper rake angle, such that the flat disappears — but no more than that.
Assuming you are working from right to left, at each gullet you are filing the face of the right tooth and the back of the left. You need to reduce the flat on the left tooth by half, and, while doing so you will finish shaping the face of the right tooth (whose flat was already reduced by half during filing in the previous gullet.) If one tooth’s flat is larger than average, press harder against it when filing — favor it, or crowd it, slightly — so that all the teeth are filed to the same shape. When you finish here, joint lightly to check your work. If the teeth are still not uniform, do the shape-filing again.
around and repeat for the rest of the teeth.
Filing
Check your file to be sure it’s still sharp. Filing is the step that actually sharpens each tooth and deserves a sharp file. Assuming the handle of the saw is on the right, and you are working toward the left, find a tooth that is set away from you. Place the file in the gullet to the left of that tooth. You want to file the face of the tooth that’s set away from you (you’ll be filing the back of the tooth to the left, the one that’s facing toward you.) It is the faces of the saw teeth are doing the cutting of the wood and filing them in the same direction that they are set allows the file to chatter less and do a neater job on this more critical surface. The surface of the back of a tooth isn’t as vital to the saw’s performance as the surface of the face, so you want the face to receive the best treatment from the file. Filing requires that you maintain three angles: rake, fleam, and slope. The rake angle guide is the scrap of wood with the file stuck in it. The fleam guide is another scrap with the angle-slot sawed in it that rests over the blade (or an angle guide on the bench behind the vise.) With rip-saws, you probably don’t need a fleam guide because the fleam is 90° and fairly easy to maintain by dead reckoning. The slope angle is the angle of the file relative to the floor. It hasn’t been mentioned yet because it should simply be square to the blade, parallel to the floor. Some saw filers adjust the slope angle in relationship to the fleam angle, but for most common fleam angles it makes little difference in the performance of the saw.
If it seems that all these angles pose something of a juggling act, you’re right. But it only takes a few teeth to get into the rhythm and keep all the balls in the air. Check your setup for all the angles and file a tooth. Don’t be surprised by the noise it makes; that’s the back of the tooth that’s set toward you that’s chattering and screeching. The closer the teeth are to the vise jaws the quieter it will be — to a point. Ear plugs are a good idea. Filing should only require light file strokes because the shape of each tooth was created during the shaping step. The goal here is to remove whichever flat spot may remain, creating a sharp, zero-radius tooth. Skip a tooth — remember, you’re filing every other tooth so that you’re filing in the direction of the set — align your file in the gullet, check your coordinates and file another tooth. slide the fleam guide as needed so that it’s a useful reference. reposition the saw in the vise as needed, too. When you reach the end of the saw, turn it around and start again from the handle end going left to right, flip the fleam guide over so it’s angled the correct way. Remember to reverse the rake guide, too, to file the proper angle on the rest of the teeth.
Setting (after filing)
Some sawyers think it best to set the teeth after all the filing is done. Pete Taran says: The conventional wisdom is to set a saw’s teeth before it is sharpened. I disagree with this approach for several reasons. If a saw is set before it is sharpened, then part of the set
is removed when the teeth are filed. It is very difficult to try to figure out how much the set is decreased in filing as it is dependent on many factors such as how sharp the file is, how hard you bear on the tooth with the file, and how uniform the saw teeth are filed. I prefer to set the saw after it has been sharpened. By setting the saw’s teeth after it has been filed, a very uniform set can be achieved, which not only makes the saw cut well, but also makes a very nice finish on the piece being cut. It only takes one or two teeth to be over-set to make the edge of a cut piece of wood ragged and rough.
Mike Wenzloff disagrees: when being set, a tooth will rotate outward at the face. For a rip, it presents the face all wrong. For a cross-cut, the fleam angle changes at the point of the set upwards to the tip of the tooth. One cannot escape this. While reducing the fleam on a cross-cut isn’t too big a deal, the rotation is on a rip. Very little set is removed if the setting is done precisely before the final light filing. It is just a couple light swipes per tooth except on the larger rip profile teeth.
Quite often, the previous setting from the last sharpening is still within specifications and you don’t need to do it again. Because, after shaping and filing, you’ve removed some of the set, why do it before hand? Make a test cut to verify. If the saw cuts well: straight and clean. Ta-da! Go saw something. If it drags or binds, add wax. If it still drags, you need to set the teeth. The set gets a little smaller with each filing but you may be able to file the teeth three or four times before needing to set them again.
If a test cut wanders off line, the teeth on the side that the saw is cutting toward are set too much. Use a fine stone on the side with too much set and gently hone those teeth a bit. Lay the saw flat and run the stone flat on the side of the blade to hone down the teeth on that side. Take one or two passes with the stone, test again and repeat if necessary. If the saw cut is difficult to control or wobbles around in the kerf, you may have too much set altogether. Measure it with the above specs in mind and if you find you need to reduce it, try clamping the teeth in a vise with smooth, metal jaws and squeezing them to reduce the
set. Squeeze a vise-worth section, advance the blade, squeeze again trying to use the same amount of pressure, advance the blade, etc. Check the cut, hone or reset as needed. Kevin
Drake adds: I much prefer re-setting over honing here, mostly because it has worked
for me when honing has just made matters worse. Besides that, set diminishes with use
so just re-setting may make a saw behave as if it has been recently sharpened.
Be sure to coat those freshly cut teeth with rust preventative. You’re done!
That concludes this three-part excerpt from The Perfect Edge: the Ultimate Guide to Sharpening for Woodworkers by Ron Hock. Thanks for reading. Now go sharpen your saw!
The Sharpening Blog 