Some of the jig saw blades of my assortment can sharpened by hand, using the same technique as used for sharpening handsaws.

However, some blades now have the same treatment as "hardpoint" saws, making the teeth very hard while the body of the blade is softer. Firstly check with an old triangular file.

You will need a 6" or 7" triangular saw file and handle.

Also, either a metalwork vice or improvised chops to hold the short blade, and a candle. Use the lighted candle to blacken the teeth so that you can see where you have worked.

• At the end of an oilstone, rub the teeth lengthwise along the stone until a small flat triangle (a shiner) is formed on the tip of each of the teeth.
• Set up a good light.
• Fix the blade in your holder, noting that the clamping end might be thicker than the rest of the blade.
• If you have a headband magnifier, or clip-on watchmaker's loupe, now's the time to use it. You should be able to see how the tooth points are slightly rounded through wear.
• Use the triangular file, following the manufacturer's angles.
• Working on alternate teeth, and the file pointing towards the blade's tip, file the front edge of the tooth set facing away from you, and the back edge of that pointing towards you.
• Remove half the shiner. Turn the blade round and file the other teeth until the shiner just disappears. This applies to cross-cut form teeth.
• For rip profiles, there is no need to file alternate teeth, just file them all the same way.
• You could manage by missing the topping stage and just file each tooth with the same number of strokes, though in theory at least, the result should be inferior.
• Some blades have teeth with a marked hook profile with, for their size, very rounded gullets. Since the radius of the arris of the saw file will not match this profile, indeed it could spoil it, concentrate on only filing the back edge of the teeth.