Dovetail & Grain

Tag: Sharpening

  • Saw Sharpening Angles

    Filing a saw is less mysterious than it looks. There are three angles, they interact, and once you have set them for a given saw you leave them alone for the life of the plate.

    Rip and Crosscut

    A rip tooth is filed straight across at nought degrees of fleam and works like a row of tiny chisels. It is the easier of the two to file well.

    A crosscut tooth wants fifteen to twenty degrees of fleam so the points sever the fibres ahead of the cut. Below fifteen it tears; above twenty-five the points crumble.

    Rake matters more than either. Eight degrees of relaxed rake on a dovetail saw makes it start without grabbing, which is most of what beginners struggle with.

    SawRakeFleamTeeth per inch
    Dovetail8°0°15–20
    Tenon, rip4°0°12
    Carcass, crosscut12°18°14
    Panel, crosscut15°20°8–10

    Set

    Less than you think. Enough that the plate does not bind and no more — every thousandth of set is a wider kerf and a rougher cut. On a dovetail saw in hardwood you can very nearly get away with none at all.

    Joint, shape, set, sharpen. In that order, every time. Doing them out of order means doing them twice.

  • Sharpening Chisels by Hand

    Sharpening Chisels by Hand

    Sharpening is the skill that unlocks every other skill, and it is the one people put off longest. It is also much simpler than the volume of writing about it suggests. Here is what we actually do at the bench, on an ordinary Tuesday.

    A chisel being honed on a waterstone with visible slurry
    1000 grit, slurry raised, working the whole surface of the stone rather than one track.

    Flatten the back once

    A new chisel needs its back flattened, and it needs it done properly one time. An edge is where two flat surfaces meet; if the back is hollow the edge is a line of scratches no matter how well you hone the bevel. Do the first 30mm and no more — nothing beyond that ever touches the work.

    Angles

    ToolPrimarySecondary
    Bench chisel, softwood25°30°
    Bench chisel, hardwood25°32°
    Paring chisel20°none
    Mortise chisel25°35°
    A degree or two either way makes no practical difference. Consistency does.

    The routine

    1. 1000 grit until a burr forms along the whole edge. Check by running a thumbnail up the back.
    2. 6000 grit, same bevel, until the burr flips.
    3. Back flat on the 6000, four or five strokes, to take the burr off.
    4. Strop if you like. It is not necessary, and it will round the edge if you push.

    Ninety seconds a chisel once the stones are wet. The reason it feels slower than that is almost always that the edge was allowed to go too far past sharp before anyone did anything about it.

    How sharp is sharp

    The paper test tells you nothing useful. Stand the chisel on your thumbnail: if it bites without pressure it will cut end grain. If it skates, go back to the 1000. Looking at the edge under a light is better than any test — a dull edge reflects a thin bright line, a sharp one reflects nothing at all.

    Sharpen when the tool stops being a pleasure to use, not when it stops working. By the time it stops working you have already spent an hour fighting it.

    Keep the stones flat. A dished stone puts a curve on the bevel and undoes everything above. A cheap diamond plate and thirty seconds a week is the whole of stone maintenance.