Files

Files are used for the removal of metal to an accuracy of plus-minus 0.025mm. They are used to square ends, file holes, file rounded corners, remove burrs from metal, straighten uneven edges and smooth rough edges. The main component is made of high carbon steel with a handle usually made from wood. Files are manufactured in a variety of shapes and sizes. The cuts of files must be considered when selecting them for different tasks.

Hand files are parallel in width and tapered in thickness. The smooth edge permits filing in corner. The parts of a hand file is shown in the figure below.

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They are classified based on the main features such as length, section, cut and grade as given below.

Length: Measured from the tip to the heel of the file excluding the tang.

Cut: Type and relative coarseness of the teeth.

• Single cut file: It has a single row of teeth extending across the face at an angle of 65^o to 85^o with the file length. The cuts are parallel to each other and its size depend on the coarseness of the file.

FIGURE

• Double cut file: It has two rows of teeth that cross each other. The first row and the second row is referred as overcut and upcut, respectively. The first row angle is 40^o to 45^o with the file length. The cuts are parallel to each other and its size depend on the coarseness of the file. The upcut is finer and shallow when compared to the overcut. The teeth of these files tend to clog more easily than single cut files.

FIGURE

• Dreadnought or Vixen file: It has a single row with its teeth curved in an arc and is suitable for heavy cutting soft metals. It has curved teeth that cuts aggressively for rapid filing and smooth finishing of soft metals and wood. The regular cut and fine cut vixen files are used for tough work on steel, cast iron, copper, brass, aluminium and other hard metals. The smooth cut is used where a superior finish is required by removing very slight amount of material.

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• Rasp file: In this, each tooth is cut separately by a single pointed tool. These files are used for coarse work on soft materials.

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Section: Cross-section of the file.

• Flat file: It is a double cut file that is slightly tapered towards the point in width and thickness. Usually one edge is left without teeth to permit working against a finished surface. Flat files are double cut on both sides and single cut on both edges.

FIGURE

• Half Round file: It is usually double cut type on both sides and tapers towards the tip. One surface is flat and the other is curved. It is a general purpose file, which can also be used for filing concave surfaces. The shape of the tool allows it to be used where other files are unsatisfactory.

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• Square file: This file tapers for part of its length and is double cut. These files are used mainly for slotting, grooving and finishing square edges.

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• Triangular or Three square file: It has a triangular cross section with its three sides each at 60^o to the others and tapers towards the tip. These files are used for filing the gullet between saw teeth, filing internal angles and clearing out corners.

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• Round or Rat tail file: Its cross section is circular and may either be tapered or blunt. These are mainly used for filing out concave surfaces and holes.

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Grade: Depth and spacing of the teeth.

• Bastard file: It is a coarse grade file used for roughing out, as it removes metal quickly.

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• Second cut file: It is the finer graded type which gives a better finish. But the cutting process takes time.

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• Smooth file: It has shallow teeth that are closely set enabling a good finish. These grade files should be used for finishing work only.

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• Dead Smooth file: It is the smoothest grade of all files.

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The following are the other commonly used files in aviation industry.

• Mill file: It is tapered slightly in thickness and in width for about one-third of their length. These files are mainly used for drawfiling.

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• Lead float file: It is a single cut type file specifically designed for use on soft metals. These files are cut more coarsely to deal with the softest metals and are available in various lengths.

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• Warding file: It has a rectangular cross section that tapers to narrow point in width. This file is used for filing in narrow spaces.

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• Knife file: It resembles a knife due to its narrower blade type. These files can create V-shaped grooves and are used by tool makers on work having acute angles.

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The following are the recommended filing methods.

• Cross filing: This method is used for squaring and roughing down. It is done by holding the file at both ends and using the files at right angles to the work. While starting the process, grasp the handle so that its end fits into and against the fleshy part of the palm with the thumb lying along the top of the handle in a lengthwise direction. The file end must be grasped between the thumb and first two fingers. During the return stroke, relieve the pressure in order to prevent unnecessary wear of the file.
• Draw filing: Once the cross filing has been completed, this methods is used for finishing tasks. It is done by holding the file in line with the work to produce a shearing effect. During the return stroke, pressure should be relieved.
• Rounding corners: This method is used for filing round surfaces. If the surface is narrow, start the forward stroke of the file with the point of the file inclined downward at 45^o angle and finish the stroke with the heel near the curved surface. By following this method, the full length of the file can be utilised.
• Removing slivered edges: This method is used to remove burred edges that prevent parts from fitting properly, thus also avoid injuries caused due to scratching and marring of parts.

The following are the precautions that must be monitored when using files.

• Always use the type, length and grade of file suitable for the job.
• New files must not be used on steel for the first time. Using them on brass or similar metals will harden them.
• Never use a file without a handle.
• Make sure the file teeth is cleaned using a scratch card or wire brush. A sharp ice pick can be used to remove clogging.
• Secure the work rigidly so that the position enables filing to be done horizontally.
• Try to use the full length of the file for each stroke.
• As the file only cuts on the forward stroke, relieve the pressure during the backstroke.
• Rubbing chalk on the teeth during the final finish produce excellent results.
• Do not strike the files on hard material as they are brittle.
• Store the files in separate racks to prevent dulling of teeth caused by bearing against each other.
• Always store them in a dry place to prevent rusting.