This article deals with restoring metal surfaces.  It’s applicable to just about any time you have occasion to pick up a file, whether to fit or repair old bronze boat hardware, antique tools or automotive parts.

My training aid is a badly abused but classic hunting rifle from 1936 I recently restored…as these objects are the subjects of close scrutiny by discriminating clients and require a degree of precision useful for demonstration.

File Pattern and Type

Files come in far too many patterns and cuts to treat in detail here, but are generally either Machinists or Engineers Files for shaping, Saw or Sharpening Files for sharpening, Aluminum Files for that soft material, Rasps and smaller Rifflers with coarse teeth for wood, Needle Files for small work or large Blacksmith Files.  There are also innumerable specialty files like metal checkering files, lathe files, curved tooth files, cantsaw files and even triangular dovetail files with two “safe” or smooth faces.

Either American or Swiss pattern Files are common here, the difference only being the pattern standard used to manufacture the file and how the fineness or coarseness of its teeth is measured.  The shapes themselves are similar, but Swiss files have longer, thinner tapers, are slightly slimmer, and are made to closer tolerances and come in finer grades of cut. They also cost more. Any edition of Machinery’s Handbook by Industrial Press will provide additional detail.

Type of Cut

Single cut files have a series of parallel teeth running diagonally across the width of the file surface and are generally used for sharpening or fine finishing.  Double cut files have two series of parallel teeth running diagonally across the width of the file surface with one series crossing the other. These are best suited for rapid removal of material.

Coarseness of Cut

Bastard Cut in American Pattern files is the standard for shaping and dressing steels and castings.  The Swiss Pattern equivalents is #00 Very Coarse.  Second Cut American is for lighter removal and for hard metals. The Swiss equivalent is #0 Coarse, with a finer grade of #1 Medium Coarse above it. Smooth Cut American is for finishing and hard metals. The Swiss equivalent is #2 Medium with #3 Medium Fine and #4 Fine above it.

Once filing skills are mastered on both metal and wood, these finer grades of file will often pay for themselves in the cost of abrasive paper saved.  Flea market machinist files too worn for steel still work just fine on wood, and will save lots of sanding and paper.

Cross Filing

Using the file in its normal direction of cutting perpendicular to the axis of the file.  Files cut in one direction only and when they get dull, they are relegated to soft materials like wood or discarded… if you develop the habit of lifting the file on the return stroke, you will literally double the life of your files.

Draw Filing

Draw filing is used to produce very smooth and true surfaces.  To draw file, hold the file at right angles to the direction of the strokes, with your hands close together to prevent breaking the file.  Pressure should not be great and can remain the same for the back stroke, as the teeth cut in both directions when using the file in this manner.