G'day Chris here, and welcome back to Clickspring.
The hand file is about as old school as it gets,
so its a great first tool to kick off this new series of engineering tips.
And as much as I love working with the lathe and mill,
there are many occasions in the home shop where hand fitting is the better way to go.
So with that in mind, here's 8 old school tips, for better hand filing.
First off, be sure to use only the best quality files.
Because the difference in durability and cut quality when compared
with the cheap imports is dramatic.
You'll see an immediate step change in the quality of your work when using good files,
and you'll enjoy the process more because they cut so well.
I use Swiss made Grobet files for the vast majority of my filing and I find them to be
excellent.
So If you're looking to track some down,
be sure to confirm that they are actually made in Switzerland before you buy,
and keep an eye out for the bunny on the tang.
Number 2: Safe edges are enourmously useful when precision filing.
Although I have to admit, it goes against every instinct to take an expensive new file
and then deliberately blunt a cutting surface.
But there really does need to be at least some differential cutting ability within the file set.
And virtually all of my files have at least one safe edge ground onto them,
if its not a natural feature of the file already.
A safe edge like this effectively isolates the cutting to a single surface,
and it forms a key part of my filing technique.
Because when I'm filing something that needs to be precise,
like for example a rectangle thats required to be dead on center.
I like to have the basic target profile formed,
very early in the filing process, before I use up too much of the available metal.
This is a lot harder to achieve if the file is cutting on 2 surfaces at once,
so isolating the cutting to a single surface at a time just makes it that much easier
to control the outcome.
Also, have a close look at the edges of the files.
Where the surfaces meet, there's effectively a bit of a radius to the cut.
So the file can never give a corner that's any crisper than that.
And often that's just not good enough for the final result.
But with a safe edge ground onto one surface,
at least two edges of the file become as crisp as can be,
and so can now deliver a sharp inside corner on the workpiece.
And while we're on the subject of corners,
they really are the key to the whole process.
Because they essentially define the boundaries of the surrounding surfaces.
If a corner gets away from me, its pretty much impossible to recover the work.
So here's the approach that I usually take to make sure that doesn't happen:
First, when removing the waste stock I make sure I leave some excess material
over the object line, to give me something work with .
A millimeter or so usually works well, but often I'll leave a little more to play it
safe.
Next I identify the critical corners of the workpiece.
These are the locations that must be well positioned for the part to be acceptable.
And then I start the cut working directly towards those corners,
with the objective of establishing the overall shape
whilst using up as little of the metal margin as possible.
Ideally I'm aiming for a slightly under or oversized version of the final profile
just short of the line.
As I get closer to the line, I shift to the finer cut files,
so that the rate of metal removal reduces, and the surface finish starts to improve.
Towards the very end, if its all going well, then I can slowly work it the rest of the way.
with light cuts, until I see the fit that I want.
And its not unusual for this last part of the process to take up most of the time.
Because there's often only a handful of file strokes between a tight and a perfect fit.
The very last thing I want to do is take it too far, and remove too much metal.
Now this idea can be applied to just about any profile, whether it be internal or external.
But it is certainly more awkward to work on an internal shape.
And the fact that the initial opening is usually a round hole,
makes it easy to inadvertently tip the final profile relative to the workpiece.
But again its a clear focus on the corners that keeps the whole thing on track.
If I get the corners correctly established early, then the orientation can be locked in.
And the whole shape can be slowly worked toward the final profile.
Now of course that's the ideal, but it rarely goes according to the plan,
which leads to tip Number 4.
Once a surface starts to trend in the wrong direction,
it can very quickly get beyond a point that's recoverable.
So I check the work often, making sure that all is as it should be.
And if I see a problem developing I'll correct that first.
Now the earlier this happens the better.
Its a lot more fun lightly coaxing a small error back into shape,
than it is to have to go deep into the margin of metal to recover a well developed error,
and so jeopardise the entire part.
For something like this wheel a constant visual check is enough
to confirm that the apex of the cut is tracking the marking out,
and that the teeth aren't being rolled to one side or the other.
But this cotter pin is a good example of where both referencing the marking out
and taking direct measurements is required.
Much like I mentioned before, the aim is to establish a slightly oversized profile,
just outside the line.
Again making sure that the key corners that define the profile end up where they should be.
But the shank on this part needs to have a light taper to perform its locking role.
So once the profile is close, direct measurement becomes the better method
to track whats happening for the final stage of formation.
Now there is an even more immediate technique that can be used to pick up errors,
as they occur.
Just prior to each cut, a light cross grain pattern can be made on the surface of the work,
and then a light can be positioned to make that pattern more visible.
The first stroke on this pattern shows how the file was oriented for the cut.
And then with each subsequent stroke its very easy to see exactly
where the metal is being removed.
I can immediately see if I'm rolling an edge, and then adjust the cut on the fly to compensate.
Its such a simple idea, and its incredibly effective.
Because it means that rather than reacting after completing a surface,
I can take a much more proactive approach while the cut is in progress.
And it makes creating a taper or dealing with a localised error easier too.
Just mark the region where more metal needs to be removed,
and then concentrate the work there.
OK, so its clear that human factors play a big role in the outcome when hand filing.
There's an unavoidable tendency for small errors of movement,
that needs to be somehow managed.
And one thing I find useful for this are the reference edges of
whatever I'm using to hold the work.
I watch those edges about as much as I watch the file itself,
because they quickly reveal any error in the way I'm moving the file,
and I can immediately correct what I'm doing.
And although the effect is quite subtle, the shop itself has a few reference edges too,
that can also help the process.
Aligning the work with the vise, and then the vise with the bench
means that all of these edges that are sitting in my peripheral vision as I work,
and can now also give me cues for better alignment of the file.
Now another way to manage the human errors is to limit the entire movement
to something that has less inclination to drift.
And a great example of this is draw filing.
When holding the file for draw filing, the file itself presents as a relatively long
reference line,
to visually confirm that the cut is being performed square to the work.
And the fact that its held with both hands
means that there's a good controlled grip to keep it that way.
So the technique is perfect for delivering a very precise surface.
Its also an excellent technique help generate the same profile
on 2 or more parts at the same time.
And finally, just a quick word about filing buttons and other filing guides.
Its one thing to file a flat surface, but something else entirely to freehand file circular shapes.
So one way to make it a lot easier is to use filing buttons.
They don't need to be anything fancy,
generally just a simple shouldered bolt design is all that's required.
Although there are two schools of thought about what they should be made from.
Some are strong advocates that they be made of hardened steel,
so that when reached the file can't cut them.
But of course that's bad news for the files.
So my personal choice is to turn them up on the lathe from mild steel,
and simply accept the possibility that they'll get slightly damaged over time.
And the same idea can be expanded to generate more complex shapes using guides,
like for example the crossings on this wheel.
The shape near the center of the wheel needs to be exactly the same for each opening,
and a filing guide makes this much easier to achieve.
OK, so that's Old School Tips number one complete.
And by no means is this meant to be a comprehensive list,
so be sure to add your own filing tips in the comments below.
Thanks for watching, I'll see you later.
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