The file is the tool most frequently used when working with metal and there are few jobs that can be completed without the use of the appropriate file. There is a wide range of files available, the basic types of which have been described earlier in the Course. You will not need every type, but there are a few important ones which should be to hand in any workshop.
The basic set, which should be adequate for general metalwork, will ideally consist of two large files -say 250mm and 300mm long. Choose one flat and one hand file, either bastard or second-cut or one of each coarseness. The flat file, which is double-cut on both faces and tapered on its width and thickness, is the best general purpose type. The hand file, which is double-cut on both faces with a single-cut on one edge, is ideal when filing up to corners since it has an uncut, or safe, edge which prevents damage to the angle upright.
It is advisable to have a section of smaller files, say 150mm long; these could be pillar. square, round and half-round types with either smooth or second-cut grades of coarseness. The pillar file has the same cut as the hand file, but is narrower for work in restricted places. The square file is double-cut on all sides and tapered for about one third of its length; it is used for filing corners and slots. The round file is double-cut on the larger version and single-cut on the smaller ones and is also tapered for about one-third of its length; it is used for enlarging holes and producing rounded internal corners. The half-round file is double-cut on the flat side and may be single-cut on the rounded side which is not quite semi-circular and is used mainly for filing out a radius.
There is a range of more specialist files, again described earlier in the Course, and it may be worth your while to invest in some of these to ensure the best results on more intricate work. These include the riffler, which is a small double-ended file ideal for really detailed work such as on jewellery and silver work.
Warning Remember that files do not come with handles and you should never use one without a properly fitted handle; otherwise you run the risk of damaging your wrist or the palm of your hand while working. Most handles are sold with a small hole already drilled to take the file tang. To ensure a tight fit, put the handle on the tang, hold the file and tap the handle firmly on a solid surface until you are sure the handle is securely fitted. Never strike the file on a surface or hit it with a hammer since it is brittle and likely to break if subjected to shocks. Remember also to store your files carefully, preferably in a rack, to avoid damaging the teeth of the files.
It is good practice to begin using a new file on brittle metals such as cast iron or brass, which are difficult to work if using worn files. When the teeth start to wear, you can then use the file to work mild steel which is not so brittle. Some surfaces, such as those of welded joints, can damage the teeth of a file; these should always be tested for hardness with an old file before you work them with a new one. You may find it necessary to remove hard, scaly surfaces on the metal you want to work; this you can do by lightly chipping with a chisel to break the scale.
When files are used on soft; metals such as aluminium and copper the teeth tend to get clogged up with tiny particles of metal; if these particles are not removed, the file will not cut properly. They can be removed by brushing in the direction of the cuts with a file card; the point of a scriber will remove any particles that are still left. Chalking can prevent a file from clogging or ‘pinning’ – it also acts as a lubricant – but it does tend to reduce the efficiency of the file when working hard metals.
Cross filing and draw filing are the two techniques used when working on metal; these have already been covered in the Course. Remember before you start on your work to practice on a piece of scrap metal about 6mm thick by filing down to a line already scribed along the metal. You can test the accuracy of your filing by laying a straight-edge or the edge of a steel rule along the filed surface; hold the work and straight-edge up to a strong light, which will show through if the new surface is not level. Even a fractional error will be obvious if you use this testing method. Curved surfaces Obviously an internal curved surface cannot be filed with a flat file; here you will have to use a round or half-round file. The main problem, however, is that unless the curved area being worked has exactly the same radius as the face of the file, you will have what is called ‘line contact’ between the two curves. This will produce a line or groove in the work if the file is moved backwards and forwards always in the same direction. To get a good result, the file must be moving along the curve at the same time as it is moving across the curve. It is essential, before starting work, to mark out the curve and to file to the marked line.