Bench Tip from Alan Revere
Most flat and square files-both large hand files and small needle files-have cutting surfaces on all four sides and on the edges. The sharp edges are great if you want to carve a 90' groove into a piece of metal, but they can be problematic for certain applications, such as finishing a bezel setting. If you want to clean up the top of a setting, a file with sharp cutting surfaces and edges all around will put the stone in danger. However, with a little effort, you can modify a file that will allow you to play it safe.
First, prepare a safe surface on one side of a fine-cut (#4 or #6) square needle file. (Note: You can also use the following steps to modify -barrette needle files, which are great for finishing prongs.) To do this, carefully lay one side of the file against the spinning wheel of a bench grinder and draw it across, removing the abrasive cuts on that side of the file. Repeat until the cuts are completely removed.
After rough grinding, take the file to an oiled sharpening stone-the kind you use to sharpen gravers, drill bits, blades, etc. Hold the file flat against the stone and rub it back and forth to smooth the new surface and remove marks left by grinding. When the surface is smooth, knock the cuts off the edges on both sides of the newly cleaned surface.
With all remnants of the original cuts removed, use progressively finer grits of abrasive paper to bring the surface and adjacent edges to a polish. Begin with 220 grit paper held against a flat surface. Proceed to 320, 400, and 600-grit. Finish up with 4/0 polishing paper. The file should shine on one side.
And with that, you have a file that is "safe" for finishing bezelsand prongs. Keeping in mind that all stones can be damaged by abrasion, place the safe surface very lightly against the stone andfile the setting to perfection.