I have decided that this is the summer when I finally finish the Kurath.
I have been playing it for some time now in its current state and feel that I have it pretty well dialed in, have the exact mouthpiece I want to use on it, etc. Now I want to "prettify" it so any future owners will have trouble figuring out exactly what is not from the factory.
This summer, I plan on making new levers and linkages that are mounted on a much nicer-looking bracket, and that will be very labor-intensive. I have the nickel silver plate from which all the parts will be cut, and it ought to be easy, if somewhat tedious and slow-going.
I need to do some work cleaning up mount points for things that no longer exist. (For example, I have a bracket to mount a thumb lever, but I do not have a thumb lever anymore.) All that mess will be cleaned up.
I believe I will run the bugle (which on this tuba is just the bell, the bottom and top bows, and the dogleg) through the Z-60 to (as Joe likes to say) slick them out. Then I plan on buffing and lacquering the assembly using my automotive HVLP spray rig. I might do the valve section, but probably not. I will do all the bits that come off, though (leadpipe, slide crooks, valve caps and buttons, etc.) and keep the nickel silver outer slide tubes polished. I will let the few brass runners and the piston case stay raw brass to make it easier to work on. That is very little to care for, allowing easy access with a torch… ideal for me in my situation.
One thing I have wanted to do for a long time is make the rotor section removable, as it was on the Holton. On this horn, with its wrap, it will take some different solutions to make that work and have it be sturdy enough to not get pranged out of alignment. And it will need a union between the pistons and rotors.
Since Conn-Selmer discontinued the three-piece component that I had planned on using for this, I was left with fabricating something, and all I could make would be one of those split collars with the wingnut, like you see on sousaphone necks. I don't like those for several reasons. So I put this off while I decided how to use my lathe to make one like the Conn parts.
When I was flirting with a 6th valve for the Holton 345, I actually built the valve/slide circuit. To shoehorn it into the very limited space in which it was to live, I needed to shorten the union between the 5th rotor and the first branch of the open bugle. I ended up getting a used leadpipe union from a YBB-641, which I knew would have to be bored out a bit to work. (A lathe project?)
It did not look promising in the photos, as these always seemed to be pretty cheap and thin, primarily used to speed assembly at the factory, not intended to be used more than a few times before it broke or bent. Having never taken one apart and messed with it, I had no idea how incorrect I was in that assumption. It is actually more robust than the Conn part. I still do not like it as much, but it is by no means the junk I had always assumed it to be.
So I bored it out to accept the Miraphone tubing it would have to be soldered to.
Done.
Now it is sitting in a box, unloved.
I have written about the Miraphone system of bore sizes and tubing wall thicknesses in the past. They only use tubing from within that system; they only need to draw those and keep them in stock. Despite this economical way of doing things, they still have many different sizes because the make trumpets up through very large bore tubas. Rather than describe all of the ones I need here by the various bore sizes, I will write about them as I think of them when I work. Everything is based on the 186 tubak, so keep that in mind.
186 — No matter how the advertising wonks at Waldkraiburg want to spin it, the 186 and 188 are .769" in bore size. Where they got .772" is anyone's guess, but it probably involves a hobeful bit of rounding and massaging the metric size upwards to make people think it is bigger than it is. However, the difference between the claimed and the actual bores is almost nonexistent, so again, it is a bit of fantasy on their part. The ACTUAL bore size as indicated on the labels on the tubing is 19.54 mm, which is dead on .769". So no arguing with me. I am correct, as this is the label provided on the parts by Miraphone. The bore INSIDE the valve is actually smaller, as most people know, so don't toss that one out for discussion.
Okay, with that having been dispensed with…
The 186 uses three tubing sizes. Their part numbers and sizes are:
003612200082
ID - 19.54 mm (.769”)
OD - 20.32 mm (.800”)
003612200083
ID - 20.35 mm (.801”)
OD - 21.22 mm (.835”)
003612200084
ID - 21.26 mm (.837”)
OD - 21.93 mm (.863”)
The 6th valve I made for my Kurath uses a custom-made valve based on the 186-sized model with a larger exit port. The 4th piston uses the same size of tubing, and the 19mm ports have been expanded by half a millimeter to accept the Miraphone slide tubing. The exit port has also been stretched like this. The 5th comes next and is one size larger.
So 4 and 6 use the first two of the tubes listed above. To keep all the tubing straight in my head, I have "named" them by the last two digits of their PN. So the 186 uses tube 82 for inner slides, and 83 for outer slides. The MTS uses 83 and 84 for the tubes. And my Kurath uses 82/83 for the 4th and 6th slides and 83/84 for the 5th slide. (I used 84/85 for the small side of the MTS.)
The Yamaha union is for the 641, which has a bore just between two of the Miraphone tubes, so I had to bore it out a bit to use it on the Holton for the 6th slide. It is the interior size of tube 85, so it is like a ferrule to go over an 84 tube or valve knuckle. I need one that fits over an 82 tube (the inside slide tubes of 4 and 6, and the exit knuckle from the piston set), so to use this union, I need shims, and that sucks, because one shim is a PITA, but two will be a
MPITA.
However, I figured out how to silver solder all that mess together so that there are, effectively NO shims. I was thinking of this backward and… well… wrongheaded. I thought I would have to carefully measure and cut the shims, clean and prep them for silver soldering, then do it all at once, which invites all sorts of nonsense.
Instead, I will use a hunk of 82 that is about 2" long and a shim of 83 cut to the needed length and silver solder these together first, then slide the Yamaha union half over that and silver solder THAT in place, cutting it off flush when it cools and has been through the pickle solution.
Silver soldering three super-thin tube ends stacked together would be difficult and require quite a bit of heat using my setup, and it would be for long enough that the union halves could warp. I have had better luck over the years, silver soldering tubes together if the ends are NOT flush, but when the inner tube extends beyond the outer, giving you an edge for the solder to flow against as it is drawn around and into the joint. If I build this from the inside out, the union parts only have to be heated one time each. Then hack off the ends flush. BOOM. Done.
The interior gap is about 1 mm larger (a 0.5 mm lip all the way around) and is very short. I may leave that, or I may make shims for that, too, but that becomes another PITA, so probably not. I have to feel it with my fingers to see what I want to do.
In the end, the Yamaha three-piece leadpipe union will go where the ferrule is in the red circle.
Making the rotors a separate assembly will make working on them much easier and faster. It will allow me to remove several assembly compromises I made to allow for work on the pistons. These will not be needed if I can simply remove the rotors altogether.
I pulled the needed tubing bits and have to unsolder the union half from the rotary valve that would have become the 6th valve of the Holton. I can use that valve/slide assembly for something else, someday. Once that is free, I can get to work making this necked-down union that will make all of this possible. I may even have the correct pin spanner here in my lathe tools for this union. If not, there is always Macmastrr-Carr…
