Notes on Using Files and Rasps 


Let's start with a brief explanation of the difference between rasps and files. First of all, a rasp is designed for the rapid removal of wood or a similarly soft material such as horn (which is basically compressed hair) or hooves (if you are shoeing horses). A file may be used on wood or metal. A file has teeth that exist as a row of uniformly raised metal. These teeth appear as little lines that go diagonally across the file. Sometimes these lines cross as in a double cut (cuts in two directions) file. A rasp consists of little individually raised teeth that may be placed in various patterns across and along the rasp body. The teeth on a rasp actually look like little teeth. On cheaper rasps, these little teeth are arranged in straight rows. The better rasps like the Nicholson Patternmaker have the teeth staggered about in a non-linear pattern so that more of them cut at one time. Staggering the teeth also smoothes out the cut while still removing a lot of material.

Before I go any further,  I really must plug a product.  You really need to buy the Nicholson #50 PatternMakers Rasp. There is also a, slightly courser, #49 for more aggressive stock removal that would be good to have, but you have got to have a #50.  These are the best things since sliced bread and all the best builders use them. It will really make your work easier. They are very expensive and very fragile so only use them on wood and be very careful with them. I am careful to stay away from other metal objects when I am using them, and I keep them in the plastic bag they came in when I am not using them. This may seem a little extreme, but these things cost $50 each and they are consumables. I try to make them last as long as possible. For your stock work, you can probably get away with just using this rasp and an 8" round bastard or 2nd cut file. 

Now that the advertisement is out of the way, let's talk about the different styles and grades of files. You can find files in almost any shape imaginable, but there are two basic systems of grading the cut of files; American and Swiss. In the American system there are three grades of files: bastard, 2nd cut, and smooth. A bastard file removes the most amount of material with the coarsest cut and a smooth file removes the least amount of material with the smoothest cut. The 2nd cut is in between.  

The Swiss system of grading files uses numbers running generally from 00 to 0, 1, 2, 3,  4 & 6.  A 00, which I have never seen, is roughly equivalent to an American bastard file. An American 2nd cut would be somewhere around a Swiss 0. An American smooth cut file would be around a Swiss 1. Generally Swiss files are used for the finer work and for finishing. I generally finish up all my metal work with a a #2 file. A #4 and a #6  file will give you an almost polished surface requiring just a final polishing with a fine abrasive.

Before power sanders and relatively cheap sandpaper, metal was filed almost to final finish. I think that it is still faster, but you do have to have more files than you will find in a modern workshop. Along with the chisel, the file is the most basic tool of the traditional craftsman. Most gun builders have a box or drawer full of all kinds of files. Before WWII, there was a trade called the bench machinist whose entire job entailed using files, scrapers and burnishers to final fit parts. These men were expert in the use of files. Sadly, modern methods of machining no longer require hand fitting of parts and the bench machinist has gone the way of the rest of the handwork trades.

As mentioned above, rasps are going to be used only on wood.  However,  your  files may be used on wood and different types of metals.   In order to maintain your files in good order as long as possible, it is  customary to separate files by the type of material with which you use them.   Most serious craftsmen have a set of files for wood, a set for brass or other non-ferrous metals, and a set for iron or steel.  The reason for this is that you need your sharpest files in order to cut the softest materials and the harder the material the faster it dulls the file.  Consequently,  you get the longest usable life from a file by using it with only one type of material.   You do have to have a lot of files in order to work this way, and I admit to mixed use of my files.  However, the more filing you do,  the more types of files you have, and given the high cost of files, this approach is probably the most cost effective in the long run.  I do have most of my files marked for the primary material with witch they are to be used.  There is a white dot on the files for use with wood, and a red dot on those files for use with brass.  The files for use with iron and steel are not marked.

One final note on mixing files,  you will need a separate set of files for really soft metals such as lead or pewter.   These metals will gum up a file making it unusable very quickly. It is actually better to scrape these metals than try to file or sand them.  I once recounted to my grandfather my difficulties filing a pewter cap for a nice walking stick.   He looked at me like I was crazy and asked me if I didn't know that you were supposed to scrape pewter.  Well, of course, I didn't.  Now I do, and so do you!  

Now that I have finished with the general information, I would like to point out a couple of things about using files and rasps that you will not find in the books, at least not the post WWII shop practice books. The first and most important thing is to cut in one direction only.  Even if you have a double cut file, it is best to get in the habit of taking strokes in one direction. Generally, you push the file away from you in a long, level stroke. You then lift the file off the work, usually very slightly,  and return it to the starting position to take another stroke. You get the best control of your cuts this way. It also usually results in faster material removal. Generally, the little sawing type strokes that a lot of people use result in an vaguely defined surface and prematurely dull your file. Not that I don't do this some time, but it is usually just light strokes to finish a surface. 

Remember that you are milling metal or wood with a file or rasp. You should use a file just like a cutter in a milling machine, confident and purposeful. You impart the shape of the rasp or file to your surface.  In other works, visualize the material you want to remove and take a strong, continuous stroke with the appropriately shaped file (or rasp) to remove that material. Control is the key here. Know what you want to remove and remove it in one long stroke. For curved surfaces, you will have to move the rasp or file around a curve as you stroke. Again, the stroke should be continuous and flowing. This is very hard to learn to do. It is like patting your head and rubbing your tummy at the same time. It just takes practice. 

When filing, make sure that your feet are firmly on the ground and that you are balanced over the work.. You need to rely on your sense of balance  to control your cuts and tell you when you are cutting level and not. Your balance is often more accurate than your eyesight in determining if a stroke is level. Your eyes can fool you and you need to learn various tricks and checks to compensate for this. At the same time, you need to rely on your eyesight to tell you when you have found the center or need to set a transition or breakpoint in a line. In the beginning, you will probably just do a lot of measuring and checking with a square.  Stopping often to check your progress from various angles is imperative. 

The second really important thing to using a file or rasp is to keep it clean.   You can use a file card for the courser files.  I suggest a brass or nylon brush for the finer files and rasps.  I particularly recommend a fine brass brush to clean the Nicholson PatternMakers rasps.  A clogged rasp will just cut slower, but a file clogged with metal will tear little gouges in the surface you are trying to file.  For this reason, you have to clean a file you are using on metal every minute or two.   I usually tap the file edgewise on the bench and run my hand up and down it to clear the little bits of metal.  This will take you about 5 seconds.  You can keep metal from building up in the teeth of the file by using chalk.   You can buy chalk for this purpose from the likes of MSC or Brownels, but sidewalk chalk for kids will work just the same.  You rub the chalk on the file until the teeth are filled.  This will keep the bits of metal out of the teeth.  You will have to re-chalk after you have cleaned the file a couple of times with your hand.   By using chalk and cleaning often, you should end up with a finished surface much quicker.  

In India's top engineering and technical school, everybody has to take a basic shop class. One of the exercises that everybody has to do is file a perfectly square 1" cube. This is sort of a Zen exercise that teaches more than just how to file, but it does that also.  You might want to try this some time.  It is a skill that you must have if you are going to build guns using traditional tools and techniques.

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