Woodworking Tip of the Day: Sharpening a Handsaw: Joint It, File It, Set It Light

This is catching the MOAM's attention today….. the handsaw hanging on the wall that "still cuts fine." You push it, it skates, you lean on it, it wanders off the line, and you blame the wood. Most of the time the saw just needs ten minutes in a vise with a file. You don't have to ship it out. A touch-up is joint, file, and set only if it needs it.

Why it matters: A sharp saw does the work and follows the line. A dull one makes you force it, and a forced saw drifts. On the dory that means a frame bevel or a gunwale scarf you get to recut. Every Western handsaw cuts on the push, and the teeth come in two flavors. Rip teeth are little chisels for cutting with the grain. Crosscut teeth are little knives that sever fibers across the grain. You sharpen them the same way, with one difference in how you hold the file.

Materials

• A triangular taper saw file sized to the saw's points per inch (ppi). Popular Woodworking's chart (Matt Cianci): 5 to 7 ppi, 7 in. slim taper; 8 ppi, 6 in. slim taper; 9 ppi, 6 in. extra-slim taper; 10 to 11 ppi, 6 in. double extra-slim taper; 12 to 15 ppi, 4 or 5 in. double extra-slim taper. Other charts are off by a size here and there. Rule of thumb from Paul Sellers' crew and Wood and Shop: each face of the file about twice the height of the tooth
• A 10 to 12 in. mill file (bastard cut) for jointing a handsaw
• A scrap block of hardwood with a slot or a square face to hold the mill file square to the plate (or a card-scraper jointing guide)
• A fine India stone or a 600-grit diamond stone
• Scrap of the wood you actually cut, for the test

Tools

• A saw vise. Shop-made from two boards is fine, a vintage cast-iron one is fine. The point is to clamp the plate close to the teeth so it can't chatter
• A file handle. Never file with the bare tang
• A saw set (pistol-grip type), only if the saw binds
• A good light and a pair of reading glasses if you're my age. You're watching for tiny shiny flats

Steps

1. Figure out what you've got. Count points per inch, point to point, not teeth. Points = teeth + 1. Then look down the toothline. Teeth filed straight across, like tiny chisels, are rip. Teeth with little bevels on alternate sides, coming to knife points, are crosscut.
2. Clamp it in the saw vise. Cianci joints with about 2 in. of blade above the jaws, then drops the saw so the bottom of the gullets sits about 1/16 in. above the jaws for filing. Any higher and the file screams and chatters.
3. Joint the teeth. Lay the mill file flat on the toothline, held square to the side of the plate in your wood block, and run it from heel to toe with light pressure. Two to four passes usually does it. Stop the moment every tooth shows a tiny shiny flat on its point. Those flats tell you all the teeth are the same height, and they're your guide for the next step.
4. Shape, only if you have to. If jointing left some big flats and some tiny ones, the teeth are uneven. Disston's manual says to file straight across at right angles to the blade first, pressing toward the teeth with the bigger flats, until they come back to the same size. A saw that's been touched up regularly usually skips this.
5. File a rip saw straight across. Seat the file down in the gullet, level with the floor and 90° to the blade from above. That's zero fleam. Rake, the lean of the tooth's front face back from square to the toothline, is usually somewhere from 0° to 10° on a rip saw (4° to 8° is common). Hold the file's angle to match the teeth you've got, and it'll stay right. Use full, light push strokes and lift the file on the way back. Stop the moment the flat on the tooth disappears. Not one stroke more. Then move to the next gullet.
6. File a crosscut saw with fleam. Same seat, same light strokes, but swing the handle off square about 15° to 25°, which is fleam. That puts a bevel on the tooth's front edge. Crosscut rake runs steeper, around 15° (12° is popular too). File every other gullet from one side, taking each of the two flats about halfway. Then turn the saw around (or swing the file the other way) and file the gullets you skipped until the flats are gone.
7. Set only if it binds. Make a test cut first. If the saw binds, set it. Bend alternate teeth the same way they were set from the factory, and only the top half of the tooth. Disston warns that going deeper can spring, crimp or crack the plate. Light is right. Lie-Nielsen sets its panel saws at .005 in. per side and its backsaws at .003 to .004 in., which they say is enough for dry hardwood. Their advice is to reset only every other sharpening, not every time. (Disston's old manual sets before the final filing. Cianci sets first and evens it out with the stone. Either works. Just keep it light.)
8. Stone and test. Lay the saw flat and run the stone down each side of the teeth once, lightly, to knock off the burr. Then cut the wood you actually use. If it tracks off the line, it's drifting toward the side with more set or burr. One more light stone pass on that side.

MOAM's shop note: The mistake everybody makes is one more stroke "just to be sure." The second that flat is gone, the tooth is sharp. Every stroke after that makes it shorter than its neighbors, and a short tooth does no work. You'll be jointing and starting over. The pro trick is to stop early and come back. And don't let a saw get so dull you need a full re-tooth. Paul Sellers says a sharpen-and-set takes him about ten minutes. Do it when the saw first starts to skate, not when it won't cut at all. Another thing from Sellers: he files his 10 ppi and finer bench saws rip and crosscuts with them too, which keeps it simple.

MOAM Out.

Sources: Popular Woodworking: Saw Sharpening 101 (Matt Cianci) · Hock Tools: Sharpen the Saw, Part 1 · Blackburn Tools: Saw Tooth Geometry · Wood and Shop: How to Sharpen a Hand Saw · Common Woodworking (Paul Sellers): Setting Up and Sharpening a Saw · Common Woodworking: Saw Files · Paul Sellers: Saws, Sharpening and Refurbishment · Paul Sellers: How to Sharpen a Woodworking Handsaw (video) · Disston Saw, Tool and File Manual (1952) · Disstonian Institute: Saw Filing · Lie-Nielsen catalog (saw set specs) · Lie-Nielsen Back Saws care sheet