A rolling blog of everyday life
on and around the workbench
As anyone who's been to my workshops knows, I'm a bit of a magpie.
I can't help it - I see what looks like a piece of junk and I think
"Ooh, that'll come in handy...one day". So I rescue it,
stuff on a shelf and leave it to gather dust until that day comes.
In some cases it's not the item itself that's of interest, but what
it contains. Take the humble hard drive, for example. It sits there
in your computer, merrily churning away, and I doubt you give it
a moment's thought...at least until the day it packs up - and you
lose your entire collection of Kenny G MP3s, and photos of cats
pretending to play the piano.
people would whip the broken drive out, pop a new one in and chuck
the old one away...which is pretty much what I do - except I take
it apart first. Hard drives are a fantastic source of precision
parts. The drive platters are perfectly flat, with a mirror finish
- and can be used as precision flat surfaces, as mirrors...and,
if you hang them up on a piece of string, as a surprisingly good
(if annoying) wind chime. There are also a couple of really strong
magnets (very handy for making tool holders), lots of tiny screws
(you never know when you'll need one), a precision motor and two
or three very nice bearings.
"All good and well" I hear you cry "but
when will you ever use them?". That's the thing - you never
really know, until you're faced with a knotty problem and need to
make something to overcome it.
In this case the knotty problem was a need to fit a replacement
pearl to a key. Normally I'd fish around in my stock of pearls until
I found one of the right diameter and thickness - and while I could
find plenty of the right thickness, I couldn't find any of the right
diameter. No big deal, just sand the edge of the pearl down until
it fits in the holder, right?
Well yes, you can do that...but it takes forever, and you'll be
very lucky if the pearl remains round. A much better bet is to spin
the pearl on a machine and either turn or sand it to size as it
rotates. But how to mount it on a machine?
The classic method is to get a piece of dowel
and simply glue the pearl on the end of it. The dowel can then be
mounted in the machine (be it a drill or a lathe) and the pearl
sanded or turned to size.
The problem with this method is that it's hard to get the pearl
aligned with any accuracy, and if you're working with a pearl holder
that's a little bit out-of-round (as they often are) you may need
to remove the pearl from the holder to test the fit as you go along.
This is a complete pain in the nether regions, because you have
to glue the bloomin' thing back on the holder each time.
I wanted was a tool that can hold the pearl in a lathe, that will
allow the pearl to be centred and turned/sanded, and that would
allow the pearl to be removed for test fitting and easily replaced
in the holder for further turning.
There's a well-known way of doing this, and it's
known as a friction chuck. A normal chuck grips the part around
its circumference so that it can be turned - but a friction chuck
grips the part on its faces. If that doesn't make any sense, just
think of what you do when you pick up a sheet of paper. You grip
it 'twixt finger and thumb. That's (sort of) a friction chuck. If
you do the same thing with a coin, and only grip it lightly, you
can spin it around between your fingers with your other hand. Engineers
will probably baulk at this analogy, but it's close enough for jazz.
There are two parts to a friction chuck; there's
the part that goes into the lathe chuck (which provides the spinning
power) and there's the part that goes into the tailstock...which
provides the friction. However, you want the tailstock part to be
able to spin, otherwise it'll mark the part...and it'll get pretty
hot in no time at all.
A really simple friction chuck is just a piece of wood mounted in
the lathe chuck and another piece of wood held against it with a
revolving centre - with the part you're working on sandwiched inbetween.
It works very well - but when you're dealing with something as small
as a key pearl, it gets a bit unwieldy. I wanted something a little
more elegant, and a lot more accurate.
what I came up with.
I took a hard drive motor apart and pulled the bearing out of it.
It's ideal for the job because it's small, and it's longer than
it is wide.
In order to make it versatile and provide a little more working
space I fitted two Delrin (plastic) 'plugs' into it - a standard
size for large key pearls and a smaller one for those little fiddly
Bis Bb pearls. And to each plug I glued a disc of rubber. This will
provide the friction...or the grip. The other part of the tool is
a lot simpler, it's just a piece of bar - again, with one end smaller
than the other, and rubber discs glued to each end. This end goes
in the lathe chuck, the other end is held in the tailstock chuck
- and the pearl is held between them.
far so good - but when you grip a pearl between the friction chuck,
it rarely runs true...and it's a complete faff trying to align it
by hand and eye. What would be really handy is a tool that automatically
centred the pearl.
And here it is - and yes, yet another hard drive had to die in order
to make this tool. It's simply a bearing mounted on a steel bar,
which is then fixed in the lathe's toolpost. The pearl is lightly
held in the friction chuck and the lathe turned on. As the pearl
spins, the bearing on the bar is slowly brought into contact with
it...and as it touches the pearl the bearing begins to spin. As
you push the bearing further in, it pushes the pearl over until
it runs dead centre (or true).
Isn't that brilliant? It takes mere seconds to centre the pearl
- so if you need to remove it to check the fit, it's a doddle to
replace and re-centre it.
Once the pearl's running true you simply snug up the tailstock to
increase the friction and hold the pearl firmly in place - and then
you can turn it.
It's unlikely to see a great deal of use as a
pearl turner - it's not a job that needs doing all that often -
but a friction chuck comes in handy for all sort of jobs. It's one
of those tools that, once you have it, you find things for it to
do. And every time I use it I'll not only have the satisfaction
of knowing I made it out of a few scrap parts, but also that it's
saving me a great deal of time - and you the price of a pint or
More toolmaking - and this time I've been having much fun with
a spot of lapping.
In case you're unfamiliar with the term, or are perhaps wondering
whether it's the sort of thing that goes on in seedy nightclubs,
it refers to the practice of rubbing two parts together until they're
a perfect fit - aided by a thin layer of abrasive between them.
OK, maybe that's the sort of thing that goes on in very
seedy nightclubs. I'll give you that.
Anyway, it's a very time-consuming process, but the resultant fit
is very accurate - and aside from the time factor, it's a very cheap
and simple way of achieving a very high level of precision.
Most of the lapping in this trade is about matching
a fit between two parts - a particularly common job being that of
lapping a crook tenon sleeve into its receiver, or a new rod screw
into a barrel. But sometimes it's necessary to lap something so
that it conforms to a dimensional standard...and in this case the
standard is flatness.
you've read any of my reviews, or the article on warped
toneholes, you'll have seen me using a lump of metal placed
over a tonehole as a means of showing the degree of warp in it.
This lump of metal is called a flat standard...because it's flat,
and because it's the standard against which the flatness of another
object can be measured.
I already had a collection of flat standards, but I needed some
larger ones...and I particularly needed some thinner ones which
could be used without having to remove any keys. These are useful
for testing brand new horns, where the removal of keys could technically
invalidate a warranty - or where the owner simply wants to know
whether to take a horn back for replacement or a refund.
I chose 303 stainless steel for my material. It's
tough, it's resistant to corrosion, it's reasonably easy to work,
it's quite stable...and I had a sheet of it lying around.
The first job was to cut some blanks out of the sheet. This was
probably the most time-consuming aspect of the operation, and after
an hour of hacksawing I began to regret not simply buying some ready-cut
discs off ebay (where they can be had for two a three quid a pop).
I'd gone for a 4mm thickness. I could really have done with going
thinner than that (2.5 - 3mm) but had some concerns about the thermal
stability of such thin standards - though I intend to make a batch
up and test them anyway. Might work, might not - but if it does,
it might provide a means for home tweakers to set themselves up
with a set of accurate tonehole testers on the cheap that can be
used while the horn is still assembled.
the blanks cut and roughly rounded, it's time to pop them in the
lathe and turn them into rounds - and to do this I used the same
chucking method as in the previous
blog entry - namely a friction chuck, though on a slightly larger
With the disc now rounded off it's removed from the friction chuck
and glued to the wooden backplate with a dollop of superglue. This
relieves any stress on the face of the disc and allows for a tool
to be run across it to flatten it.
At this point the disc is probably quite usable. It's not perfectly
flat across the face (typically slightly dished towards the centre),
but if placed centrally over a tonehole any minor dishing is going
to be largely irrelevant...and it'll at least be flat enough to
give you a general idea of the state of the tonehole.
As I'm going to be using these discs as reference
standards, I needed to go the extra mile and make sure they're as
flat as possible, which meant they had to be lapped - and in order
to lap something flat you need a flat surface against which to lap
it. But how do you know that this surface is flat?
Well, you could buy a lapping plate - and you'd know it was flat
because it would come with a certificate...and a hefty price tag.
Or you could make one. This is the beauty of lapping - you don't
need a bunch of expensive machines and sophisticated measuring equipment
- you simply need three blocks of metal (usually cast iron, but
certain other metals can be used) that can be lapped against each
other in turn...and, after a lot of puffing and swearing, you end
up with three plates that are dead flat and which can now be used
as lapping plates.
all sounds marvellous, but in fact it's rather unnecessary given
the tolerances required. You could lap a disc on a sheet of 600
grit carborundum paper glued to a thick sheet of glass and it'd
be well within the level of accuracy needed for the job. So why
bother going 'the full English'?
Mostly it's because I can, but also because it's nice to know that
my flat standards are really flat - and because I
use them in the course of my reviews to point out manufacturing
defects, it's only fair that I ensure the standards I use are beyond
I used a two-stage lapping process - a coarse
lap to rough out the larger imperfections followed by a fine lap
to sneak up on the final flatness, and to add an appropriate surface
finish to the disc. In this case it's a matt finish I'm aiming for.
I lapped the previous set of standards to a mirror finish...which
is lovely and took forever, using ever-finer grades of abrasives
- but the reflective surface turned out to be a proper nuisance
when using a leak light during tonehole levelling. Just goes to
show...sometimes you can overdo a thing.
Speaking of which, you wouldn't believe the amount of gloves, tissues,
rags, mineral oil and degreasant I got through in knocking these
very much a process of 'do a bit, clean up, check it for flatness,
do a bit more'.
And despite it being very grimy work you have to be so very careful
to avoid contamination of the lap and the workpiece, because the
slightest bit of grit in the wrong place at the wrong time will
mean having to go right back to the start of the lapping process.
It's immensely satisfying though, to the point where you almost
have to force yourself to say 'enough is enough'. And nothing beats
dropping the finished disk onto a flat surface and having it stick
to it due to the vacuum between the surfaces.
And while I was at it I knocked up a set of flat
abrasive discs. These aren't used to level the tonehole as such
(as you would with a rotary or large flat file) but rather as part
of my preferred method of levelling, which is to selectively treat
only the high spots with a small smooth file and then follow up
with the abrasive discs to knock down any tiny peaks. It takes a
lot longer than going at the whole tonehole with a file, but it
removes less metal and provides rather more accuracy.