blog of everyday life on and around the workbench
More recycling - but with a twist this time. Two twists, in fact.
I'm sure you all know by know that I love fixing things - and that
I like to do my bit towards saving the planet/whales/badgers/Muckinese
Battlefly - but the need for a very specific tool in the workshop
gave me the chance to repurpose something I'd already repurposed.
had a problem, y'see, and a sticky one at that. A great many of
my tools are made from steel, and I often find that (for one reason
or another) they become slightly magnetic over time. This isn't
so much of a problem for screwdrivers - in fact it can be a useful
property at times - but it's a proper nuisance on cutting tools
such as files, drills, scrapers and reamers etc. For files in particular
it can be a serious issue because particles of steel can stick to
the file and thus be dragged across the work...which can really
ruin a finish, and your day.
It's a common problem which is why there exists
a device called a degausser, which can eliminate an unwanted magnetic
field. It gets its name from the term for a unit of magnetism -
the gauss - which in turn is named after very clever chap called
Carl Friedrich Gauss who, among many other great achievements, was
a pioneer of the study of magnetism (though the term 'degaussing'
was apparently coined by Charles F. Goodeve in the 1940s).
The device is essentially a conductive coil, through which an alternating
current is fed - any item passed in close proximity to the coil
will have whatever magnetic field it possesses obliterated. A typical
use for a degausser is in the wiping of data stored on magnetic
media, such as a computer hard drive - but they're also often found
in production lines, to remove magnetism from parts that have been
previously passed down the line with the aid of powerful electromagnets.
they tend not to be cheap - or at least a decent one isn't - which
is why there are plenty of blogs and videos out there which tell
you how you can make one yourself. Unfortunately, again, they all
seem to be based around using coils of wire and fairly hefty AC
currents...and that's really not a field (spot the pun) I have much
However, there's another way to make a degausser - and one that
better suits my skills.
The degausser works by providing an alternating magnetic field (a
standard magnet has a static field), and while this is easy enough
to do this with electricity, it's also possible to alternate the
field mechanically. In simple terms this means flipping a magnet
so that its poles (north and south) point one way...and then the
other. And you've probably already guessed that this isn't something
you can easily do by hand. At least not for very long.
So I made something that could either be spun
in the lathe (for degaussing small items) or in a cordless drill
(for larger items). That's twist No.1 (geddit?)
I actually made it quite some time back, or most of it at least.
It was originally designed to be used as a magnetic base for a dial
indicator, and was made out of a lump of scrap brass and three neodymium
magnets salvaged out of a couple of old hard drives. And that's
Although the magnets are quite small they're really rather powerful,
and if you're not careful they'll stick together with enough force
to give your finger a nasty nip if it gets in the way.
I simply turned a slot in the brass then glued the magnets in place.
Worked a treat, but when I replaced the dial indicator with a smaller
one which came with its own magnetic base, I no longer had any use
for the one I'd made - so it sat on the lathe cabinet for half a
It was only while browsing for degaussers (and
baulking at the prices for an industrial one) that I chanced upon
a video of a chap who'd made a mechanical one, at which point it
occurred to me that I had half of one stuck to the side of my lathe.
Each of the magnets are fitted with opposing poles facing each other
(north, south, north, south etc.) - and all I needed to do was to
mount the thing on an arbor and put a thin cap on it (makes it easier
to slide items across the face of the disc, and to remove any particles
of metal that adhere to the face). So I knocked up an arbor out
of a rusty old bolt, screw the disc to it and then covered with
the lid from an old aerosol can.
the degausser is spun on the lathe and a tool is dragged across
the face of the disc, it's subjected to a rapidly alternating magnetic
field which destroys any field present in the tool.
If that sounds rather confusing it might help to think of a tennis
match at Wimbledon. Yep, we're gonna have an analogy.
Before the match starts, all the punters are looking in different
directions. Some people are chatting to those next to them, some
are looking left, some right and some straight ahead. Some have
even dozed off. This is a reasonable description of the state of
the atoms in a piece of non-magnetised steel.
Once the players are on court and playing, the crowd's focus alternates
between left and right. In either of these two states you could
say that the crowd had been magnetised. If you were to freeze them
at one state or the other they'd be a permanent magnet.
When a workshop tool become magnetised it's usually only weakly....just
enough to pick up a few iron or steel filings - which would equate
to a particularly boring tennis match where only a small percentage
of the crowd were paying attention.
Now...imagine the players began to play at ten
times their normal speed. The crowd simply wouldn't be able to keep
up with the pace of play, and at any one time you'd have some folks
looking one way, some the other...and the rest halfway. There'd
be chaos and confusion - and if you suddenly removed the players
from the court, the crowd would remain in this state.
This is what the mechanical degausser does. The file that's being
passed across its face is the crowd, the spinning disc is the speed
it works a treat.
It works at relatively low speeds (300 rpm) but I find it's most
effective at 1200 rpm. One pass of the tool is usually sufficient
to demagnetise the tool. In fact it works so well I think it'd be
worth mounting it on its own motor - just to save having to fire
up the lathe every time a tool needs the treatment.
I have my doubts about the protective cap though. It's virtually
impossible to hold a tool close enough to the disc without it being
drawn onto the face. It also feels rather strange...sort of 'lumpy'.
Of course, if you drag a file across the plastic it's going to wear
through it eventually. I could put a thicker piece of plastic over
the face, but that would reduce the effectiveness (it'd reduce the
strength of the degausser's magnetic field) - so maybe I'll think
about making a disc that can be easily replaced.
Or I could just bung some gaffa tape over it. It's cheap, it's easy
to replace, relatively tough and thin enough not to reduce the magnetic
And the best of it is - I have nice big roll of
gaffa tape...that I found in the middle of a road.