Which file do I need, and how do I use one properly?

Safety

What you'll need

• Files in the shapes you need, with handles
• File card or wire brush
• Vice or clamps
• Chalk (optional)

Step by step

1. Choose the shape by the surface.Flat or hand file for flat surfaces and outside edges. Half-round for concave curves and for general use, because it does both. Round or rat-tail for opening out and truing a hole. Square for slots and rectangular recesses. Triangular for internal corners, for sharpening saws and for deburring. Warding files are thin, for narrow slots.
2. Choose the cut for the material and the stage.Cut refers to how coarse and how the teeth are arranged. A single-cut file has one set of parallel rows and gives a smoother finish; a double-cut has two crossing sets and removes material faster. The grades run roughly bastard (coarse), second cut (medium) and smooth (fine). Start coarse to shape and finish fine.
3. Understand a rasp.A rasp has individual punched teeth rather than rows of cut ridges, and it removes timber very fast at the cost of a rough surface. It is for shaping wood — a chair leg, a curved edge, a fitted joint — and it is a shaping tool, not a finishing one. A cabinet rasp or a hand-stitched rasp is much finer and leaves a surface that needs little cleaning up.
4. Know the Surform and the modern alternatives.A Surform is a perforated steel blade in a frame that grates timber and clears its own waste through the holes. Fast on softwood, plaster and fillers, useless for a finished surface. Modern carbide-toothed rasps and shaping tools do the same job with a much better finish.
5. Fit a handle before you use it.Every file's tang goes into a handle, pushed on firmly. A bare tang is a spike. This is not a nicety.
6. Clamp the work and stand square to it.Work at about elbow height, with the workpiece low in the vice and the area being filed close to the jaws so it cannot ring or flex. Stand with one foot forward so you can push through the stroke with your body rather than your arms.
7. Push, do not saw.A file cuts on the forward stroke only. Press down as you push, and lift the file clear on the return — dragging it back under pressure blunts the teeth and does nothing useful. Use long, full-length strokes.
8. Cross file, then draw file.For an accurate flat edge, first file across it at an angle in one direction, then change to the opposite angle so the new scratches cross the old. The crossing pattern shows immediately where the high spots are. Finish by draw filing: hold the file at both ends with its length across the work and push and pull it along the edge, which leaves a much smoother, flatter surface.
9. Keep the file clean.Soft metals, especially aluminium and brass, pin the file — small fragments wedge between the teeth and then score the workpiece. Clear them with a file card, a stiff wire brush made for the purpose. Rubbing chalk into a new file's teeth reduces pinning considerably.
10. Look after them.Files are hardened and brittle. Store them so the teeth cannot touch each other or anything metal, keep them dry, and never use them as a pry bar or hit them. A file with rounded teeth is finished — they cannot be resharpened at home.

Tips

• Files are much more useful than most people expect: opening out a hole a fraction, deburring a cut, easing a hinge that binds, fitting a key, truing a sawn edge before routing it.
• Needle files — a small set of assorted shapes — are worth the very small cost for fine work, model making and easing tight fittings.
• For shaping timber, a rasp then a file then abrasive is the traditional and still the fastest sequence from rough to finished.
• A new file is very sharp and cuts fast. Keep one good file for finishing work and use the older ones for rough jobs.

Common mistakes

• Using a file without a handle — The tang is a spike, and a file that catches drives it straight into your palm.
• Dragging the file back under pressure — It cuts only on the push stroke. Pressure on the return rounds and blunts the teeth for no benefit.
• Using a wood rasp on metal or a metal file on green timber — A rasp's punched teeth are not hard enough for steel; a fine metal file clogs solidly in timber and is very hard to clear.
• Rocking the file through the stroke — It produces a convex edge rather than a flat one. Keep the file level and let the crossing scratch pattern show you where the high spots are.

Questions people ask