blog of everyday life on and around the workbench
I had an interesting job come in last week - a client wanted a custom
thumb rest made for her Selmer MkVI alto.
Actually, if I'm being completely honest it wasn't so much that
she wanted it...it was more that I persuaded her it'd be a substantial
improvement on the existing setup.
yes, it's entirely functional. It does the job of raising the arch
of her small hand over the palm key touchpieces whilst still allowing
the use of the octave key. In all the important aspects it does
just fine...but it looks bloody awful. It doesn't feel that great
either - the cork makes the thumb rest a bit squishy under the thumb
and the octave key touchpiece is too grippy.
I piqued her interest by telling her that I could design and build
something that would look much nicer and would feel far more responsive
- and that it wouldn't actually cost a very great deal. Better still,
it would be completely reversible so that should she ever wish to
sell the horn the modifications could be easily removed and the
horn restored to its original setup.
There are a couple of approaches to this very
common problem, the easiest and cheapest of which is to modify the
thumb rest/octave key - but where this isn't possible (or desired)
the next option is to look at modifying the palm keys. If the player's
hand isn't that small you might be able to get away with simply
bending the keys a little, but if more space is required under the
hand then it's quite likely that one or more of the palm keys is
going to have to be 'cut and shut'.
What this means is that the riser on which the touchpiece sits is
sliced in half, then a portion of material is removed to bring the
touchpiece down to the required height before the key is silver-soldered
back together. The big drawback with this mod is that it's difficult
and relatively expensive to undo...unless you happen to have a spare
set of palm keys lying around. I tend to recommend thumb rest mods
as a first line of attack simply because, as this client has done,
it's very easy to lash something up with a few bits of cork and
see how you get on with it over a period of time. If it works for
you, you can then think about a more robust solution. A lot of players
opt for mods made out of Sugru
- which is an excellent and cheap way of solving ergonomic issues
- but it's never going to as elegant as a handcrafted custom mod.
As far as this job goes there were two requirements;
to fit a raised thumbrest and to adapt the thumbrest to match.
We discussed the option of fitting a teardrop-shaped thumbrest,
which provides support to the rear of the thumb - but it became
clear that such an option would be wasted given the angle at which
the client's thumb sat on the rest, and having a slight roll-off
on the leading edge would be of more use. As for the octave key,
I proposed a rather more domed touchpiece canted at an angle towards
the rest. This would allow for a bit of overhang of the thumb without
triggering the mech and still provide a slick and responsive feel.
All that was left to do was to choose the material for the thumb
rest. Plastic's (usually Acetyl) a common choice and is easy to
shape, but it's a bit boring and some players can find it's a bit
slippery. Brass or bronze is nice, but it can get expensive when
opting for anything other than a round thumbrest - but the client
chose to have the rest made out of a nice piece of cocobolo wood
that I'd salvaged from a plinth made to hold a sporting cup. It's
a good choice - it looks attractive, it feels great under the fingers
and it's very easy to cut to shape.
took a few measurements and set to roughing out the thumbrest. The
first thing to do after cutting the wood to roughly the required
diameter is to sort out the base of the rest. It sits on a stub
that's fixed to the body of the horn - and I could just bore out
a piece of wood to fit over the stub and fix it in place...but it
would leave the sides of the rest standing proud of the tube, which
would look a bit odd. So the bottom of the rest has to be profiled
to match the tube.
There's no point doing anything else until you get this bit right
If you've done your maths properly the base of
the rest should sit on the body tube at precisely the same time
as the bore in the rest meets the top of the stub. This isn't too
critical - though obviously you don't want the bore to be too short
or the base won't meet the tube...but a millimetre or so over-long
isn't going to hurt, and it leaves some space for the glue.
I am sanding the base. There's a little bit of trial and error involved
because the body tube is tapered - and if you don't match that taper
on the base the rest will sit at a slight angle. It won't be by
much, and it's probably not all that important, but it'll be just
enough to be noticeable if you know what you're looking for.
The sanding tool is just a piece of wood that's been turned to just
under the diameter of the body tube where the thumb rest stub sits
and some emery paper glued onto it( which brings its diameter back
I also have a little sanding rest attached to a tool holder that's
set so that the centre of the rest matches the centre of the sanding
tool. This is the most critical alignment of the sanding process,
and with that taken care of I can focus on the small adjustments
needed in order to sand the base at a slight angle.
It's time for a test fitting, and straightaway
there's a problem - the top D pillar is fouling the thumb rest and
preventing it from sitting on the body tube.
No big deal though because I'm going to add a 'beauty feature' that'll
take care of it - namely a taper on the bottom of the base. This
narrows the diameter of the base so that it slips neatly into the
gap between the thumb rest stub and the D pillar and adds a bit
of interest to the shape of the rest.
The big trick here is to cut the taper so that the upper edge lines
up with the apex of the tube.
could, of course, work out the taper mathematically - but by the
time you've taken a few measurements, dug out your calculator and
worked out the angle of the dangle and set the lathe up to cut the
taper, the pub will be shut and you'll be driving home in the dark.
Far simpler to cut a partial taper, check it against the horn then
make any adjustments necessary. Trial and error again, in other
If it all goes wrong at this point it'll mean
having to sand the curve deeper and cutting a bit more out of the
bore so that you can have another bash at it...or you could rescue
the job by rounding off the bottom with a file rather than go for
Luckily for me, I got the taper right on the second go; the bottom
of the rest now just clears the pillar and the top of the taper
sits right on top of the apex...which, rather annoyingly, you can't
see because there's a pillar in the way. It's a good fit over the
stub and the slight taper I've sanded into the base means the rest
sits perpendicular to the body...but only one way round. The rest
now has a front and a back, and if you turn it 180 degrees it'll
sit at an angle...so some care will be needed when it comes to the
the bottom of the base sorted all that's left to do is to cut the
rest to the right length, profile the top and tidy it all up - but
before I do that I'm going to cut a groove in the bore. It's a snug
fit over the stub, so this groove will provide a small reservoir
for the glue and should ensure a sound joint.
Here's the completed thumb rest sitting in place.
It hasn't been glued on yet - I have to sort out the thumb key and
service the horn - and with all the keys off, that tall rest will
be quite vulnerable.
you can see I've given the top a very shallow dome and rolled over
the edge slightly. This should provide the most efficient profile
for the client's thumb, but I won't know for sure until they try
it. If it fails to please it'll have to be adjusted until it's right
- but I think I've nailed it. I've opted to finish it with French
Polish - which is simply shellac dissolved in meths. It's a traditional
finish and one that suits exotic hardwoods, and I think you'll agree
it really brings out the richness of the colour. However, I haven't
gone all out and gone for a mirror finish because that tends to
hide the grain of the wood and makes it look like a lump of coloured
All I've done is apply what I'd call a sealer coat - which is one
coat of polish that's allowed to dry and is then sanded back, and
repeated three or four times. It smooths out the surface and seals
the grain without completely covering it. This is particularly important
on the top of the rest, as the grain will provide some grip.
Now that the thumb rest is done it's time to modify
the thumb key and match it up.
This is a pretty simple job - I'm just going to replace the cork
with a piece of brass. I could bend the existing touchpiece up,
but it's quite a thin and flat piece of metal and there'd be little
scope for rounding it off. It would also be difficult to undo should
anyone wish to return the horn to its original spec.
There's really not much to this process other than soft soldering
a piece of brass to the key and filing it to shape - though I did
shape that roll-off on the right hand side before soldering the
brass on because I want to minimise the risk of filing the original
key. That said, some remedial work will be necessary to tidy up
the gouges from someone's previous attempts to align the key.
this stage I'm not bothered about the angle of the touchpiece, the
aim here is to get the edges cut back flush with the original touchpiece
and work on rounding off the top of the extension piece. Once the
final shape of the key hoves into view it'll be time to think about
adjusting the necessary angles. With those tweaks in place it'll
then be possible to adjust the surface profile of the touchpiece
and thereafter tidy up all the edges...and smooth out those gouges.
said it was a pretty simple job, but just look at the number of
files I used on it.
It's a lot, I know, and the medium cut half round (4th from left)
did the bulk of the work - but I find it's always worth picking
up a different file even if it's just to make one or two strokes
rather than using one that's not quite the right cut or shape for
the bit you're working on. It's also an immensely satisfying job
- with the caveat that there comes a point where a couple of careless
licks with a file can completely ruin the lines (or the look) of
And if you're wondering what the yellow paint is for, it indicates
that these files are for non-ferrous metals only (brass, bronze,
silver etc.). If you use a file that's been used on steel there's
a chance that particles embedded in the file will score the surface
of a much softer metal...which can really ruin your day if it happens
near the finishing stage.
much filling, tweaking, sanding and polishing, the key is finished.
It looks a lot neater now that the old gouges have been smoothed
out and I'm very happy with how the profile of the touchpiece blends
into the top of the thumb rest. The very last job will be to glue
the thumb rest in place, and for this I'll use a low strength epoxy
adhesive. It'll be strong enough to ensure the rest doesn't fall
off with use, and with the application of a little heat from beneath
the stub it'll be possible to remove the rest without trashing it.
Of course, none of this counts for anything if
it doesn't work for the client, and I'm happy to report that - rather
appropriately - it got the old thumbs up without the need for any
It's a lot more comfortable than the lash-up job that was on there
before, and a great deal slicker in operation. And once the octave
key tarnishes it should all blend in just nicely.