The Kurath is on the Bench Again

[the elephant]

Okay, so the complete rebuild of the rotary valve section has begun. The goal is to adjust the 5th and 6th slides to where I have determined I want them to be, to finalize a bunch of angles, and to make the rotary section removable from the piston without weakening anything.

To accomplish the last in that list, I have three braces to add. These are all at locations that I decided upon last year. This is a low-priority thing that will come at the very end of all of this work.

The slide lengths… I did the math on all of this and compared my numbers to what Herr Kurath installed, and his were bang on. However, some things were flat. In fact, it was anecdotally told to me that this horn was one of two sent directly to Mr. P to preview in his studio before CMC was to start carrying them. It has a LOT of weird things in it that suggest to me that it was finished in a big hurry, and that perhaps he was out of certain tubing sizes and did not have time to draw what he wanted, or maybe he lacked some of the sizes he wanted. (The bore goes up and down a few times, and not by enough to make any difference, but more like some of the tubing was mismatched. Stuff like that is all over this tuba.) And when Mr. P had it, he took a hacksaw to the 1st slide because it was *that* flat.

So I went ahead and shortened all slides by about two inches because I want my slides to be about an inch or so when in tune. Just because.

Well, I have decided that I want to not only lengthen the tubes to what he used, but I also need to go beyond that on three slides. Luckily, though my tubing supply is running low right now, I have everything I need. This tuba is a very large F tuba, and the inside bore of the large side of the main slide is just a whisker over an inch (1.008")! The small side is .837".

The main issue is that to make all of this removable, I have to take apart some of the most important alignment points for reassembly. So it will be a bit fiddly to assemble. Today, I made a straight tube that tapers from the needed .769" to .837" by telescoping successive tubes, and used that to align and tack-solder the halves of the Yamaha leadpipe union that I modified last year.

I have torn down and rebuilt this rotary section several times now, and stopped with all the buffing and pretifying, so right now it looks like doggie doo. In fact, a lot of the horn looks like that. I have a LOT of cleanup work to do. I also changed the angles of the two rotor cases to be more in line with the piston set.

Tomorrow I will measure and cut the four new MTS legs. Then I will install the small outer leg to the rotary valve section and brace that to the bottom bow, using the very nicely aligned MTS as my alignment guide. Once that is done, I will rebuild the main slide.

At that point, the work will be mostly done. I will have to cut and install those braces, and then the cleanup can begin. The location/clocking of the rotors will take some time because it is a tight space, and I will have to take care that nothing touches. I have already discovered a disappointing oversight on my part regarding the clocking of the rotors. I need to do some fiddling around with the rotary section to see whether I can do what I had planned, or if I will have to do it a little bit differently. Not very happy about that, but in the end, it is a small thing.

It felt good to be in the shop again. The last few days have been small things. Today was a real workday of eight hours, lots of loud music, and only one minor burn… heh, heh, heh…

I took all of this apart and put it back together. All I did was wash it off with Dawn and hot water. I will clean the messy solder work tomorrow and buff it later. Still not finished. The two outer tubes on the upper slide need to be made about two inches longer, so that will have to be first. The modified Yamaha union has been installed, though, which is nice.


Here are the four tubes that will become the lengthened legs of my MTS assembly.


Here is the other half of the Yamaha union. Again, most of this is previous sloppy soldering that I ut off cleaning up. And about five years of patina…


Probably a stupid choice on my part, but this is the Yamaha union holding the rotor section on its own. I wanted to see the new valve case alignment. I think this will work nicely.

[the elephant]

That Yamaha union got a short write-up last year when I first decided to use it on the Kurath. I had planned to add a 6th valve to my Holton 345, and would have used this union as a part of that project. However, I ended up dumping the whole idea. For the Kurath, it was far too large, and the one that would fit was made by Conn-Selmer… and discontinued.

So I decided to shim it down to fit. This involved two shims, and so that they would not leak or come apart when hit with a torch, I silver-soldered them into the union halves.

I had to add a step inside the final piece that was essentially a piece of the tubing it was supposed to join, to cover over the small gap left when I installed the shims. This inner "lip" fills the gap between the end of the piston and the rotor case knuckles AND provides a tiny protrusion to bridge the same gap in the other half, so it is seamless through the union, despite my having to mangle it to suit my needs. Weird, but it works really well.

Original three shims right after silver-soldering. The second one got trimmed down right after this. The inner one was trimmed, and the whole piece was filed flat.


At the end of the part, you can see the very thick original part with two shims in place, and another shim inside that covers a weird little gap because Yamaha parts are metric and Miraphone parts are not.


The 3rd, interior shim was to fill this gap, and it actually is silver-soldered inside this piece and fits inside the receiver of the other half, as I said above, like a little lip.


This shows the altered part, down to an interior bore that matches the Miraphone tubing I am using at either end, with the little lip. The black is Sharpie ink. (Sorry.)

[the elephant]

I FOUND MY BOX OF DETACHABLE BRACE PARTS!

[bloke]

For that midterminal, I'm not sure whether to go red or blue.

[York-aholic]

I FOUND MY BOX OF DETACHABLE BRACE PARTS!

Now, if only I could find the .750 detachable (threaded) collar I bought from Buckeye Brass. Let me know if it happens to be in your box of detachable braces.

[the elephant]

Will do, Chief.

PS - It's not.

[York-aholic]

Nope, just found it in the wrong box.

Sincerely,
Happy Camper

[the elephant]

Just tossing stuff together to set up the space where everything needs to live. Most joints are only half-filled, and are super sloppy due to the wicked trembling in my hands (f-ing meds).

Once it is all dialed in, I will take it all down, clean it up, and very carefully solder it together, both completely and neatly. I will buff it to a high state and allow nature to give it the patina love… with the help of Renaissance Paste Wax, which keeps stuff shiny for about 6 months to a year, but allows it to darken up at the same time. Or so I have been told.

The way I wanted to save some time by lengthening the main slide ended up costing me hours of wasted time, BUT less tubing, so win some, lose some. However, I discovered that the doglet was under some stress all these years, so I will realign that as I install the MTS tomorrow.

I think my main slide legs are about a half inch longer than I want, so I will fix that tomorrow as well.

I installed the two Edwards braces between the 4th and 5th slides, too. So the pistons are held to the bugle via four body braces, a large brace that doubles as the platform for the 5th and 6th levers, and the unions at the leadpipe and the rotary valves. The rotary valves are held to the pistons and bugle via the union to the 4th, the small side of the MTS, a brace from the MTS to the bottom bow, and two between the rotary and piston sections.

I am still worried about flex, so I might add one more, but not until I have played the thing for a while.

It is almost done, and I am excited to finally get to cleaning up everything. Best things I have done to this horn?

added 6th valve
much smaller leadpipe
evened out the goofy bulges in the taper

Lots of other things have been done, but these top the list that have made this excellent tuba even better for me and how I play.


It was way too short after I added the 6th valve. Now it is too long. I'll fix it tomorrow.


These are the two braces I felt needed to be installed to replace the single fixed brace. It felt weak with not all of the anchor points attached. It should not feel weak *ever* to my way of thinking. If some of them should become loose, the structure should still be rigid. Still messing around with that…


This is easily the ugliest work I have ever shared with this community. In the past, each day ended with cleanup work for the photos to share here. I am beyond that now; my work is what it is. And it will be clean when I have finished.

[the elephant]

Well, everything went wrong today. HAHAHA!!! (I am working on laughing when things don't work out, rather than stressing and cussing.)

I won't go into what did NOT work. Rather, I ended up completely disassembling the main tuning slide and its two outer tubes from the tuba.

I cleaned up everything and looked at some photos to confirm my guess as to the new length, and decided that I can leave what I have alone and it ought to be pulled about a half inch. Or I can cut off half an inch from all four tubes. Not sure which route I will go, but whatever…

My parallels almost do not fit this slide, so I am only reasonably certain it is parallel and coplanar. I will check again tomorrow after I make a small adjustment to my setup. Then I will brace the two outers together with a detachable brace. The big leg has a fixed brace to the bottom bow, and the small side comes off with the valves, so it has a detachable brace to the bottom bow, and now there will be a detachable brace between the two outers.

I need to retaper the ends of the dogleg and the top bow because the ferrule is way too large for this, with a gap of about 2mm all the way around on both ends. I messed with its position years ago and suspect there has been a small leak there ever since. Also, it is off from the new MTS location by about 3mm.

Everything is going nicely, now…

Red Circle: The near (small) side is closer to the camera and is fully seated. The other is only partially seated, but the dogleg is bending over to meet the end of the MTS; I did not want to force it on all the way. Heating the dogleg-to-top bow joint will allow it to pop into position. Blue Lines: The top one is a factory brace and has given me an alignment point for years when working on this tuba. The bottom one is a detachable brace that will go back on when the MTS has been fully sorted. The middle is the one I intend to add in a few days.


Here is the dogleg-to-top bow ferrule. It is a looooong dogleg. I have to remove it and fit the ends to the ferrule a lot better than Herr Kurath did.


The odd thing is that the 18" long dogleg is sort of free-floating. It is soldered to the top bow and to the MTS. That's it. Nothing at all is braced to it.

[the elephant]

The MTS is more or less done. I have to install the waterkey bracket and nipple. I also want to trim the small side inner tube by the smount shown in the photo so that the other side seats fully when the slide is in all the way. (Stuff like that bugs me.)

Also, once I have it wired down, I need to move that brace on the left. It is too low (well, high). I also have to move the dogleg a little to get it to line up better with the MTS. Then I can solder both ends of the outer slide to the valves and bugle.

Whoopie!