Sub Module 7.3 Files (ESSAY)

 

EASA MODULE 7A
Sub Module 7.3
TOOLS

Files

 

Files are cutting tools for removing metal from a surface and are made of high-carbon steel. The blade is hardened, whilst the tang (to which, a handle must always be attached, for safety reasons, before the file is used), is left in a softer, tougher condition and is, therefore, less brittle. Hand files are classified by their:

•  Length
•  Shape
•  Cross-Section
•  Cut
•  Grade

The length of a file is measured from the shoulder to the tip of the blade. Files are available, for special work, in lengths from 75 mm (3 in) to 350 mm (14 in). The most common sizes are 150 mm (6 in), 200 mm (8 in) and 250 mm (10 in). Files are available in a variety of shapes (refer to Fig. 3.9), and the most common shapes are those which are:

•  Tapered
•  Parallel
•  Bellied  
   
  

 

Shapes of Files

The various shapes and the cross-sections of files allow them to be used on a wide range of tasks. The standard file cross sections are:

•  Hand (Flat)
  
•  Round (Circular)
  
•  Half-Round
•  Square
•  Three-Square (Triangle)
  

 

The Hand is the most commonly used section for general filing; and the blade is usually parallel in shape. One edge may be without teeth, to permit safe working against a finished surface. Such a file is called a ‘Hand Safe Edge’ (HSE) file.

The Round section is used in association with bellied, parallel and tapered blade shapes, with the bellied being the one most commonly used. These files are suitable for filing small radii.

Half-Round files are mostly associated with bellied-shaped blades. Such files are suitable for use on work of irregular shape or for filing large internal radii. 

Square files may be bellied, tapered or parallel in shape. They are used for internal work.

Three-Square (or Triangular) files are, usually, of the bellied shape. They are particularly useful for filing internal corners.

 Cut of Files

The ‘Cut’ of a file refers to the arrangement of the cutting teeth (refer Fig.2 below), on the blade of the file. The pattern, in which the teeth are cut, will depend upon the type of material to be filed. The common cuts of files are the:

•  Single Cut
•  Double Cut
•  Dreadnought (Curved)
  
•  Rasp

The Single Cut file has its teeth cut parallel, in a single direction and (for general engineering), usually, at an angle of approximately 60° to the main axis of the blade. This type of cut is relatively open and the teeth do not clog easily. Sometimes referred to as ‘Floats’, single cut Hand files are,
chiefly, used for filing hard metals. Round files and the curved surface of Half-Round files are usually single cut.
 

The Double Cut file also has one set of teeth cut at an angle of 60° to the centre line of the file, with another, crossing set, cut at angle of approximately 75°. This is the most widely used type of file for general purposes. 

The cut of the Dreadnought’s teeth, make this file especially suitable for heavy cutting on broad, soft metal surfaces. Its use is generally restricted to the larger sizes of flat files.

The teeth of the Rasp are ‘cut’ with a punch, while the metal is hot, at the time of manufacture. This type of cut is used for filing very soft materials such as wood and leather.
 

Manufacturers will cut files to cater for a wide range of specialized materials, such as encountered when working with aluminium and other non-ferrous alloys. 

Grade of file:

The ‘Grade’ of a file refers to the depth and spacing (number of teeth per inch) of the cutting teeth in a similar manner to the size and spacing of the particles employed on abrasive papers and wheels. The rate of cutting and the finish given to the work is determined, to a large extent, by the grade of the file.
 

While there are several more grades of files, available from manufacturers, the most common grades (or degrees of coarseness) of the single and double cut files, found in a typical aerospace technician’s toolkit, are the:

• Bastard
• Second-Cut
• Smooth

The Bastard is a comparatively coarse grade of file and, though the number of teeth per inch varies with each manufacturer, the Bastard file has approximately 30 teeth per inch. It removes metal fairly quickly and is intended, primarily, for roughing out, but may be used for the entire work, if the finish is not important.

The Second-Cut files are finer (40 teeth per inch) and, consequently, give a better surface finish to the work, but are slower cutting.

Smooth files (50 to 60 teeth per inch) enable a good finish to be obtained, but such files cut comparatively slowly. They should, therefore, be used for finishing work only.

 

 

EASA MODULE 7 ESSAY QUESTION:

How are files classified. Briefly explain each type.

(Note: Please write down your answer in the comment section below)