About Files and Filing

Files, Rasps and Abrasives

Metal shaping and finishing is mostly about resolution – how fine and how close the cutting is relative to the metal surface.  Machine lapping is the highest resolution generally available in industry – the resolution is extremely high, with a working surface that’s measured in angstoms and close-graded abrasives.  That’s not a jewelry technique, generally.  The lowest resolution is going to be found in offhand abrasives – sandpaper.  That is coarsely graded abrasives on a paper or cloth backing.  In other words, a machine lap can yield a surface that is so flat that it requres a laser to find problems.  Comparitively speaking, a sandpapered surface is barely flat at all.  Somewhere in between is the best tool for doing anything resembling precision work by hand – the file.

Rasps resemble files, but there is a key difference, which also defines the two:  rasps are forged or something like it, and files are cut.  To make a rasp, the maker gets a piece of hot steel and raises the teeth by manipulating the soft metal under fire.  A file maker gets a piece of cold steel and cuts each tooth with a file cutting machine.  The main difference between the two, aside from the fact that rasps are generally of a coarser tooth, is that files are “precision tools” while rasps are not.  That means that each tooth of a file is the same height as every other tooth, and the valleys between are the same depth, all within human limits, of course.  The teeth of most rasps will vary considerably because of the method of manufacture and the inherent fact that they are intended for rougher work to begin with.

So a file gives you resolution in your hand – equal cutting edges in a format that provides rigidity for them – it’s made out of steel.  Further resolution is that there are grades of files.  I won’t go deep into the differences between American Pattern and Swiss Pattern, except to say that the jewelry industry uses Swiss Pattern files exclusively.  Swiss Pattern files are numbered:  00, 0, 1, 2, etc., getting finer as the numbers get larger.  More resolution:  finer and finer teeth, all in a rigid format.  Files are cool, and incredibly useful.

One of the more important things to know about file cuts is that it varies with the size of a file.   This, and  more about files is here:  http://www.grobetusa.com/Products/grobetswissprecisionfiles.html

Look at the scale of cuts for the sizes – a large #2 file will have fewer teeth than a #2 needle file.  In reality, a #2 needle file is finer than a #2 ring file, though they are both #2 files.

There are a bewildering array of shapes and sizes of files, but it’s really not that complicated.  Size is simple:  use the biggest file you can, but scaled to the work, too.  Big job, big file – small job, small file.  Shapes really come down to some fundamentals:  Flats, arcs, edges and points.  You can use any flat file on any flat surface, though there’s usually an “optimum” shape.  Arcs go from the round file into more gentle arcs such as the 1/2 round or crossing.  Again, those can be used for any arced surface that they suit.  Edges vary from the hard edge of a square or triangle file down the softer edge of the crossing file.  And points just means that some files have parallel edges, and some come to a point, which can be important at times.  What this means is that it’s not required to own each and every shape of file.  A 1/2 round gives a good flat and a good arc, a square gives 90 degree angles, and a triangle gives small flats and a good notching tool, too.  And the round is a true circle, coming to a point on the tip. Much can be done with just those four files, in varying cuts.  I’ll point out that a 1/2 round ring file has a stronger radius on the rounded side that a standard 1/2 round file, in order to get inside rings easier.  Lay the two on a table top on the flat side- the ring file will be taller and narrower than the standard 1/2 round file.  Plus there is much value in safe edges – sides of the file that have no teeth at all, allowing you to file right up to an edge without cutting the edge, too.  Barrette and pillar files, among others, have safe edges.

Using Files – The Good Part

There is much advise about using and maintaining files, almost all of which comes from filing steel.  It’s important to understand that, while files should be used carefully and properly, they are still cutting tools.  If you use them, they will wear out and need replacing.  Much advice I’ve heard amounts to saying, “Treat them like fine crystal, don’t actually use them.”  No, they are tools, and they are for doing work.

I don’t use file handles.  For one thing, I have 35 files in my tray, and another 20 put away.  For another, I almost never use the tang, either.  Much advice, again, is for filing a piece of steel in a vise with a 12″ monster mill file.  Then you would have a handle, hold onto it and stand back and whale away at it.  I’m more usually working on some tiny little thing, or even a ring shank, and I’ll hold the file itself in my hand, putting my force directly onto the teeth.  I’ll talk about force in a minute….  Yes, theoretically your body oils and salts can corrode the metal – my files will be dull long before that becomes a factor.  The other bit of mixed advice that I’ll get deeper into is “The file only cuts on the forward stroke, so release pressure on the back stroke.”  That is true.  It is 1000 times more true in steel than it is in non-ferrous metals.  Which is not to say you should ignore it, but novices take that and when they file they go “slap, slap, slap”, because you’re supposed to lift the file, right?  Well, not exactly, no….

You control the path of a file with your wrist – you cut with your shoulder.  Properly used, a file is a powerful tool.  Get above the work, or a posture that puts you in a line with it, and push on that sucker.  I can take the better part of a millimeter out of silver on a single stroke, given the right file and workholding.  It’s not crystal, it’s a cutting tool.  You need to pay attention and not snap a $20 escapement file, too, but you still cut with your shoulder – that’s your power.  By the same token, ideally work should be mounted in a vice or other work holder.  Failing that, there are a multitude of methods of supporting work on the bench pin – that’s what it’s for.  There is no other way to use a file.  Holding the work in one hand in mid-air and scraping a file across it with the other isn’t filing, it’s hand exercises.

Look at the teeth of a file – you’ll notice they are cut at an angle across the face.  That means that on the forward stroke the teeth are actually shaving the work.  The work is sliding down the tooth as though it were a knife blade slicing it.  It’s not a “chop”, it’s a slice.  The main force of a file is in that – the forward stroke.  The other stroke with a file is drawfiling.  That’s when the file is laid a right angles to the work.  If you put rectangular stock in a vice and face one end of it, and then hold the tip of the file in your left hand, the tang in your right, and lay it down across the rectangle, that is drawfiling.  You push the file forwards, and catch the teeth at an extreme angle, taking extremely fine cuts.  Even more important than that is that there are cuts everywhere in between.  You can hold a file in the standard pose and push straight ahead to remove material quickly, and then you can keep the same posture but roll your wrist a bit, changing the angle of the teeth with much more of a finishing cut..  That’s the real art of filing, right there, catching the teeth just right for the jobe to be done…

And don’t go, “slap, slap, slap” because every time you lift the file you lose your reference, which I’ll get to next.  If you watch someone who’s skilled with a file it may look like they’re “scrubbing” (sometimes they are..).  What they’re really doing is “push, release, push, release”.  It’s just pressure, or not, that does it.  If you’re really just knocking off material you might lift the file, if you’re establishing edges then you lose your place every time you do that.  Oh, yeah – generally you want to file from finish to rough, not from rough to finish.  That means you file, and then go from there into the work yet to be done.  If you back up into the new material and file into your previous work you are filing it again…  Put the file on the previously filed surface and then file ahead, into the raw surface..

How To File

It’s pretty obvious that the file has two main uses – shaping and finishing.  Finishing is pretty clear – make the surface finer (lower the resolution) to prepare for polish, so I won’t belabour that.  There are some methods that are useful for shaping, though, that I’ll discuss.  First thing, again, is resolution.  You simply cannot get a fine surface and edge with a rough file.  The teeth are too big, you just can’t do it.  Use the rough file for roughing, if it applies, and use the finer files for finish shaping.  That’s important because you need to remember to leave enough material for further filing.  #1 mistake is probably rough filing to the final shape, and then there’s no place else to go and the edges are all ragged….

Let’s make a 1/2 round wedding band in sterling.  We’ll roll out some rectangular stock maybe 1.5-2mm thick and whatever width.  Depends on the ring.  It’s reasonably straight but the edges are ragged and etc.  Cut it to length and solder it into a ring shape.  File the inside clean and round it on the mandrel.  This gives us our “reference”.  A filed circle around which the rest of the ring will be shaped.  Then file one edge flat and clean and square to the circle.  That’s our second reference – use dividers and measure from that edge across to the width desired.  Saw if necessary or file THAT edge flat, clean and square.  Now it’s a parallel band.  If we needed to adjust the height, we’d measure that FROM THE REFERENCE – the inside, filed edge – and file the outside.  Otherwise we’d just file it clean, and square.  Now we have a ring that has 4 filed, square and parallel edges, and we’ll dome it.  Take your file and put a flat bevel on the outer edge – lower the top edge down towards the center hole of the ring.  Leave a uniform sized edge, and make the bevel exactly the same all around.  You do that by watching the size of the facet.  Do it again on the other side, and then what you will do is bevel it again – this time your bevel will start in the center of your first bevel, and extend to the center of the ring, on top.  Finally, you’ll do it even again,  between the previous ones.

I realized in writing the above that it’s probably really confusing, but here’s the point:  you make reference points, take off from those always, use faceting (the file cut should be uniform) and then you cut the facets smaller and smaller, using your references, until they disappear.  That way you’re not just guessing, you always have something guiding you on your way.  And there’s a methodical system, not just a maze of surfaces with nowhere to start:  Surface, square to that, measure across, surface, angle, angle, done.  This is a simple example, but it applies everywhere.  You solder down 6 wires and need to file them into tapered pillars – first file them all the same height, that’s your reference.  Easy. 

In a similar way, you can lower an entire surface by a given amount.  Get a piece of stock, and scribe a line around the perimeter where you want to remove stock.  Depending on the application, it might be an imaginary line…   Put a bevel on the corners, all around, down to that line (nearly to it is usually better).  Now all you need to do is take down the center until you reach the place you filed to at first.  Instead of starting out blind, first you make the reference marks, and when you join those marks by taking down the center material, it will just “magically” be right.  Also easy….

Start from a precision edge, file a precision line, still a precision piece, over and over again.

I use a #0 ring file for roughing, and a #2 and #4 for finish.  I use the needle and escapement files I mentioned above most of all, but equalling or warding files are also most useful, at least to me.  They’re the same except the warding is pointed.  I also have a barrette shaped escapement file that I’ve ground the point down on the safe side, so it’s like a knife blade on the end, with teeth on it.  Handy.  I also keep most small files till they are dead – there are times when you want a dull file, not for cutting but for getting a very fine finish in an awkward place…..  Keep filing – good exercise, too…..

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johndonivan

Latest posts by johndonivan (see all)

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