A rolling blog of everyday life on and around the workbench

01/08/2019: 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.

OK, 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.

I 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.
Here 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 on size).
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.
You 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 words.

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 a taper.
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 final fitting.

With 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.
As 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 plastic.
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.

At 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.

I 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 the piece.
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.

After 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 further tweaks.
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.