The Great Kurath Re-Tubing

[the elephant]

Thermal Expansion Issues

A — First of all, King brace feet do not have the little vent hole through the flange and socket. Secondly, I cut the rod to the *exact* length needed to fill the voids in the brass sockets. And Thirdly, I believe that this rod is actually pure nickel and not nickel silver.

Thermal expansion is not usually much of an issue, but in this case, I think I made the rod too long. I will trim 2 mm off and try again. I suspect also that the nickel rod might lengthen a bit when heated, and then shrink back to its original length as it cools. Pure nickel will expand at a different rate than yellow brass and nickel silver. Its use was a purely cosmetic choice and may have been a poor one. Either way, trimming it to give me a millimeter gap in each socket ought to take care of that.

The vents are needed as this rod fits tightly, and I put flux into the socket to ensure the solder flows fully fills the joint. I noted that as the flux boils out with this tight rod that you can see the rod get pushed out a tiny bit as the gas escapes. Having a vent for the expanding gas will help. I will also try to sand down the rod tips a bit to loosen the fit and allow space for the gas to escape without trying to move the rod outwards.

Trimming down the rod and adding the vents should take care of the three-piece brace introducing misalignment.

B & C — I think I have been thinking about this backward. I have been soldering flange B down first, allowing stuff to air cool for about ten minutes, then heating the free end C until the solder will flow, and then quickly floating the flame to the thin nickel silver tubing, running in a bead and then allowing it to cool.

Every time — and I mean EVERY time — as it cools, the slide assembly, which worked pretty well using only two fingers (and no lube), suddenly become STUCK. The very thick bracket is expanding down its length quite a bit. The solder cools and firms up first, and then the thick brass shrinks back to its original length. This pulls the bottom ends of the tubes together by nearly a millimeter! The free end C also flexes like a snake a little bit. This is enough to make the slide nearly inoperable.

SOLUTION — I will try to attach free end C first. I will use some of my thermal putty, but it is thick enough that I suspect it will still pass a lot of heat down the skinny portion, causing at least *some* flex, if not actual lengthening. I will cope with any small gap left between the slide tube and flange B. It is a normal brace flange, so I will use the thermal putty around the end of the thick bar and focus on heating the edge of the flange disc and getting solder in the gap of the parts that are not directly under that huge heat sink. I think this will allow me to heat and attach that end without the bar causing misalignment as it cools.

Further, I *might* also add a flange to free end C so that both ends have a portion of "normal" material to try and solder down without having to directly deal with the thick stock Kurath used for this part. I would rather learn to do it as is, though, because Herr Kurath did it that way. If I simplify the problem by adding a circular foot to the free end that would feel a bit like cheating to me. Of course, one more failure and my pragmatism will kick in and that flange *will* get brazed to the bracket.

I am out of Heat Fence, but our local AirGas store sells something similar. If I can't get any I will immerse the slide in a shallow tub of water with just the section to be heated exposed to air. Either way, if I look at this as a welding problem of attaching .125" steel to .375" steel without warping anything, I think I can get this slide fully assembled and back onto the horn with it running perfectly. I am really close right now, and by all things sane I ought to leave it alone.

But it pisses me off when an inanimate object tells me, "No."

So I will build this slide over and again until I learn to correctly handle the complications. I have *never* had a slide this difficult to assemble that also needed pretty much perfect alignment. I need to find out how Herr Kurath did this. I think there is a benefit to learning this, as it could help me to turn simple problems into non-problems.

I will tear this all apart again this afternoon. Fingers crossed…

[bloke]

I am bad about inserting one or three piece braces that are the perfect width, when all of them always must be narrower than perfect, because more stuff goes in there, along with the brace.
Someday, maybe I will learn.

[Tubajug]

Thanks for the detailed reports elephant! Lots of things here I never considered when doing my projects. Now I know!

[York-aholic]

Yes, quite interesting problem to tackle. As one who has warped a few things welding, I feel your pain.

Out of curiosity, and because I have no idea, what is that thick bar for (ie what does it attach to)?

[the elephant]

I am bad about inserting one or three piece braces that are the perfect width, when all of them always must be narrower than perfect, because more stuff goes in there, along with the brace.
Someday, maybe I will learn.

THIS ^^^

Exactly. I try to be too accurate, and end up shooting myself in the foot. There needs to be some *slop* built into measurements outside of telescopic tube fitting or valves in casings. I never remember to factor that in, as I am so concerned with taking (and reproducing) accurate measurements. I leave out the needed gap for the solder. On a slide, that tiny bit of error will cause it to not run very well. I am too smart to be this stupid.

[the elephant]

Yes, quite interesting problem to tackle. As one who has warped a few things welding, I feel your pain.

Out of curiosity, and because I have no idea, what is that thick bar for (ie what does it attach to)?

It is the bracket for the 5th valve lever. I *will* be replacing it at some point. I might try to purchase the one currently used on the Willson 3200 XL, but I don't really like where that one puts the thumb joint. So in the end I will probably copy that, but make it fit and work the way I need.


This is the valve section from below, and you can see the bracket holding the thumb lever in place.

[the elephant]

I am also considering going back to the original thumb ring, which mounts to the KNUCKLE rather than the outer slide tube. I hate the bracket but could improve on it some. The ring itself is wonderful. I like it much better than the Jürgen Voigt one I have on the horn currently.

Original, non-adjustable thumb ring with a mounting bracket that looks like an 8th Grade shop project but with that fantastic Cerveny-like thumb ring…


The current, much nicer setup, but with the smaller ring I do not like as much…

[bloke]

I (sometimes, but not always...) luck out with about .010" - .015" too loose, and barely bending the two tangent surfaces down to touch (whether round or diamond). The heat weakens those bent-down contact points, and the solder follows...

bloke "hell..I dunno...??"

edit
Kurath instruments experience random comment:
You probably are NOT a "lime-ish" person. Luckily, I'm not.
That having been said, I have seen - in particular - Kurath-made instruments' yellow brass (lower copper alloy than some...??) end up getting rotted out by several owners/players...typically/sadly: tubing knuckles that are permanent parts of instruments.
Being an owner of one, I kept a close watch for a few years, and then realized that (fortunately) I wasn't hurting mine.

[the elephant]

In that regard, I am okay, as well. Thanks for the information on that, though. I will keep this horn under permanent observation re red rot and lime buildup.

And now…

GREAT SUCCESS!

Once again Borat stopped by to tell me how much of a moron I have been, and he put it together for me. I am quite pleased with this…

He would not stick around for the great unveiling, so it is just fat-boy me in the vid, and Bing. He's there, too…

[the elephant]

Well, installing it to the horn F-ed up something a little bit, so I need to look at it again — LATER.

It is on the horn again and it works pretty well, but that heavy thumb lever bracket just SUCKS to work with. I did not get any thermal putty and I forgot to chill it with wet rags, so I got what I deserved. However, everything is better than it was before, it looks nice, and I did my clean-up work as I went, so I only have a little bit to do tomorrow.

Nice!

I have decided to finish the horn, then make a new lever and bracket that is not only where I want it and operates in the manner I prefer, but is not so thick that it alters slide alignment when installed. I have the needed materials, so this *will* happen. I mostly tossed this monkey from my back. Mostly.

Stupid monkey…

[bloke]

good work !!!

I'm triggered by "the color of anger", though, so I know you won't mind this.

Merry Christmas !!!

[the elephant]

No problem.

[bloke]

Where's the "atomic-thank" button?

...The upper #4 slide (with the stop rod, etc.) on my Hol-dwarf-ton (which I pull IF "low E-flat" is desired) has "gone to sh!t" - as far as "sliding nicely" is concerned...I have no idea what happened to it...unless someone whacked it on a gig, and didn't tell me...

slides: ' can't live with 'em...' can't live with out 'em.

[the elephant]

My orders from Otto Frei and Miraphone are out for delivery, the knowledge of which perked me right up. I have been pretty sick with some stomach bug since the day before Thanksgiving, and have spent a lot of time in bed sleeping. Perhaps today will be better.

[the elephant]

WARNING: Contains Overly-Technical Blah-Blah

Okay, this project has several goals, one of which was to adjust the length of several slides, especially 5th, which was about four inches too short! (2" of pull x two legs)

Another goal was to address the weird bore profile. Herr Kurath decided to use 18 mm for 1st, 2nd, and 3rd, with 19 mm for 4th, and 20 mm for the 5th rotor, but then the MTS crook balloons up suddenly from 20 mm at one end to 24 at the other. That is a very fast taper rate in such a short run of curved tubing. In the photo, you can see how weird this looks, and if it looks weird the chances that it *is* weird acoustically are definitely worth looking at if the horn has any issues.



I have altered the bore profile in a way that is fully reversible. It also does not make large changes, so the fact that the piston ports have not changed will not affect much. I mean, it is a TUBA and not a trumpet; there is room to fudge a lot of stuff. I think Herr Kurath did this, as do most makers of tubas. I am just fudging things in a different manner that might suit me better. (Again, if not, I can always put things back.)

Below is a list of the old bores with the new numbers. I am trying to remove the slow step up followed by the big step up. What is have tapers a little more evenly. However, this leaves the 3rd circuit almost three-quarters of a millimeter larger than it was, and the 4th about half a millimeter larger. So 3rd will increase a little out of proportion.

The upshot is that the numbers look really bad, but the tubing I am using is all Miraphone, using their system of stacked telescopic tubes. There are a lot of digits in each part number, so I will limit this to the last two digits.

For this horn, the smallest stuff is tube 80, which is nominally 17.95 mm ID, and the original Nirschl-made spec was 18 mm, so this is basically zero net change.

Tube 81 is the outer slide material for 1st and 2nd.

For the pair of 3rd slides, tube 81 is the inner material and tube 82 is the outer stuff. The Nirschl-spec was still 18 mm but the new stuff is 18.73 mm. Yeah, taking it from 18.00 to 18.73 looks like a bad thing, but seriously, it is less than a millimeter on a large bore instrument. Again, this is not a trumpet, where a millimeter increase in the bore is a huge deal. For us, it just isn't that big of a deal.

For 4th I used tubes 82 and 83, which are the two used on the Miraphone 186/187/188/et al. The nominal ID of tube 82 is 19.54 millimeters. Herr Nirschl used 19 on this valve set for 4th. So I have bumped the bore again, but about a half a millimeter this time, so even less of an issue.

The 5th valve is nominally 20 mm, and I used Miraphone tubes 83 and 84, with 83 having an ID of 20.35 mm, and this same set will be used on the small side of the MTS.



The large side of the MTS was what I was trying to bump DOWN just a tiny bit. From the leadpipe to the dogleg the bore increases in weird spurts, with the taper of the MTS crook being sort of ridiculous. The MTS of this horn has a huge 24 mm large side ID. I chose Miraphone tube 87 for the inner leg of the MTS, which has an ID of 23.59 mm, so it knocked off 0.41 mm of the bore on the large side as it enters the bugle.

Now I have to see how the end of the dogleg matches up with that. He did some weird stacking of parts at this point. I suspect some internal voodoo was done; it looks like he made the dogleg too large and had to stack some ferrules to make the already overly large slide leg even bigger. After discovering Mr. Rusk's hidden work to the cut joints of the bugle of my Holton 345 I am actually really dreading opening up the MTS joints. But I have to do this. The tubes on this horn are of very soft brass and have worn down so that they are all loose and leaky. This tuba needs the new tubing. And all this weirdly-sized stuff is what I have access to, so there it is.

If it all works out well and there is no "woof to embrace" ($1 to Donn) Then the final step would be to replace the 5th rotor, slide assembly, and the small side of the MTS to 21 mm and open up the small end of the crook one millimeter, which is easy enough to do. Bringing the large end down by about half of a millimeter will also not be a problem. So hopefully none of this will affect the tuba negatively and might clean up some things. Tightening the MTS crook down a bit while opening up the rotor might be just what I have been looking for with this horn. And — again — I can always put it back the way it was.

In the process of researching and ordering all of the tubing needed for this project, I discovered that Miraphone sells some heavier-walled LARGE nickel silver tubing. I ordered a set to see what it was like. I need it for an upcoming project, and WOW! this is some seriously large tubing!

003612200689
NS
ID - 25.60 mm (1.008”)
OD - 26.46 mm (1.042”)

003612200690
NS
ID - 26.50 (1.043”)
OD - 27.66 mm (1.089”)

Thems some bigguns.


Sorry that this is out of focus; my one-handed camera operation does not always yield good results. The smaller tube inside them is a 186 inner slide leg. (Tube 82 - .769")

[the elephant]

Just farting around, spinning my wheels. No *news* to post, but I *did* work today…

I worked on a whole carload of child-sized violins and violas yesterday and today… like 32 of the dirty, little buggers.

I hate fixing the feet, top curvature, and resetting itty-bitty bridges, and tapping errant sound posts back into place. But I am broke and hustling work where I can.

I got to work on the Kurath again for about two hours. I mostly lapped, mated, and marked each of the tube sets and bagged them for storage. There were a few mildly *mooshed* sections of some of the raw tubes from Miraphone, meaning that once the drawing garbage was cut off the ends the tubes could not be drawn one through the other. Some were quite good and only took a little bit of persuasion to make them run decently enough to start cutting them.

I found some areas I could fix and two that I had to cut out and save for ferrules.

That left me with some decent tube pairs, but some still needed to be lapped in order to work well. Once I was happy with things, I then "mated" each pair. I play with them, checking the action with the inner tube in both possible ways, testing the pull from each end of the outer, so four are tested, and I then mark the one of those that pulls the best. I also check all the outer tube ends to see if there are flaws in the ends. Sometimes, after all this work, I will belatedly discover that one tube has an end that is not perfectly flat or square. If I cannot easily fix that I flip that end to be on the valve knuckle and mark it so as to hide the flaw by rotating it to a place that is not easily seen. I started doing this on the Eb Holton project years ago, which was why I tooled up my shop in the first place. This was an easy way to hide suspect work on my part. I still do it out of habit; it is probably a waste of time but whatever. I still find the occasional flaw, so once in a while, it pays off.

Once I have the end that will accept the slide, I find the ferrule that best fits the joint. Since I do not make bad cuts very often anymore, this also is probably a waste of time, but again, you just find things on occasion, no matter how careful you are. This is a LOT of tube cutting and I am still using my primitive method of rolling tubes with a jeweler's saw. [At least I burned through the almost useless 6/0 blades and am back to using the much beefier and faster cutting 4 blades. If the blade size has a "/0" in it the thing is tiny, smaller than a #1, with the number getting larger as the blade becomes finer. So a "6" and a "6/0" are at the opposite ends of the spectrum, more or less. Idiot here knows this now.]

So, every set of three tubes has been gone over carefully to check for the best fit and appearance. What is in the photo is each set of three, stacked together, and marked. In the photo, in each set, the top is the ferrule and the bottom is the outer tube, with the inner tube in the middle. Again, this is both of the 4th slides, both of the 3rd slides, and the 2nd slide. The 1st and 5th slides are already on the horn. The MTS will not be done until everything else is finished and the horn is screwed back together. (One leg attaches to the bugle and one to the valves, so everything must be set up 100% as it would be to play the horn or the MTS will be inoperable. If all seven screws are not locked down very tightly, the smallest jar to the horn can misalign the MTS quite badly. I have had this happen once just after I finished the removable valves. I learned from that and have had no issues since. This is my most used tuba, so two years of daily use with no issues other than that single event says this design works very well.

[the elephant]

I have had terrible issues with thermal expansion causing major slide misalignment on the first valve slide. The bracket used by Herr Kurath (of Willson, in Switzerland) is huge. I think he had to make it massive because he did not want to pay double the price for nickel silver. The *only* nickel silver on this tuba is the four knuckles and the rear cap of the Meinlschmidt 5th rotary valve. He almost always silver-plated his Kurath-branded tubas.

I have read in several places that he only made five of the F tubas in lacquer. However, lacquer became commonplace for him when he revamped this horn to make it into the Willson 3200-FA-5 a few years later, so his tubas started to have some nickel silver trim. (I read a quote by him that said essentially that if you plate the horn, why bother with the nickel silver bits? You can't see them." Ah, yes, this is so. But some of the nickel silver stuff you *should* have been using was for strength and wear resistance.

Anyway, had this bracket been made of nickel silver it would have been much stronger and could have used half the material. And half the material would have required a great deal less heat, thereby greatly reducing the thermal expansion issue.

The bracket would lengthen as it heated, and once the solder flowed it was at its maximum length. The slide but and the solder would cool quickly on one side and freeze together, and the bracket would cool a bit more slowly, but as it cooled it would shorten its span to the original length, which would pull the two tubes together causing the slide to bind up as though it had been soldered in place. Heat it back up and the slide would once again work perfectly.

Also, the very thin tubing would become misshapen just a bit from all the force applied to it when it bowed in the middle. (Both ends were aligned well and did not move, so this bracket was causing the two outer tubes to bow inwards toward one another.)

Solution: I despise the thumb lever. It operates in a manner that sets my designer's teeth on edge. It is completely counterintuitive to how I think. It rotates on an axis that is 90º off from where *I* think it ought to be. The center of the lever was twisted off by about 20º because the bracket was 20º off of the perpendicular from the plane of the arc in which the lever needed to travel. It was an ugly, horrible design that was a genuine kludge for such a nicely made tuba. It was a disappointment.

Today I rotated that damned bracket so that it is parallel to the valve casings and I made a new lever that is more or less in alignment with the entire valve section and not a bunch of compromises. (I know this was an early prototype as it has had a lot of adjustments to the slide lengths done at the factory and under the lacquer. Pitch adjustments were made by shortening the slide crooks and ferrules rather than the slide legs. So the final pitch of the horn was able to be dialed in without cutting up the actual tuba at all. Then Dan Perantoni took a hack saw to the 1st slide to remove about an inch on each leg. It was tragically ugly work, too. But you can play everything on 1st in tune, so there is that…

I think that Herr Kurath had issues with that bracket, too. Most Kurath and Willson F tubas have this trick little bracket for the thumb lever and thumb ring that attaches to the 1st valve knuckle. I do not think it even contacts the slide assembly at all. Very clever, and very nicely made. My horn does not have this, but this bracket was also very nicely made. I suspect this was his first attempt. Later Kurath tubas moved to the new bracket specifically to avoid this sticky little issue of thermal expansion distorting the outer slide legs. One bit of evidence is that the slide has a factory-cut leg that ends right where the top of the bracket sits. He simply chopped off one of the legs to relieve the misalignment binding. Amazing. So the 1st slide has always had this stupid-short pull length. Now it is much longer as both tubes touch the valve knuckles when the slide is all the way in. As Borat says: GREAT SUCCESS!

I am MUCH happier with this tuba now that the thumb lever is something I like, and I have an EXCELLENT 1st slide. The much longer 5th slide also makes the horn more playable.

I can't wait to get back to work on this when I have the time. The 2nd, both of the 3rd, and both of the 4th slides are next. After all that I will begin investigating what the weirdness is in the main slide. I have tubes that (again) do not match exactly, so some fudging will be needed to make the ends of the Kurath tubing meet up exactly with the new Miraphone tubing. I am sort of worried about the MTS and may hold off until I have identical nickel silver tubing for it.

Thanks for watching and reading!

Merry Christmas to those who celebrate!

Here is a short YouTube video. I will include photos in the next post. I do not script or rehearse my videos, which is why they sort of suck. I think I said everything in this video at least twice. Sorry…

[York-aholic]

Ah, much better!

[the elephant]

PHOTOS…

MAKING A NEW THUMB LEVER: Step One — drill out your hinge tube because the existing bracket is drilled and tapped for hinge rod that is larger than anything you have in stock, and your only hinge tubing fits that smaller stuff. Hmm… So I had to drill this out progressively using four drills to get it up to size without mangling the inside of the tube. I marked my bits with tape "flags" for depth, then I trimmed the drilled out part to length. I did not want to drill down into the tube more than needed at that would ruin it for the hinge rod I bought to use with it. I almost perfectly nailed it, as the last half millimeter of this little tube did not get fully drilled out. I fixed that with a round Swiss file and then some lapping compound using the hinge rod that will live there. The result is a snug fit with no play that turns very freely. Nice.


In this photo I am checking the fit of the hinge tube on the rod with it installed in the bracket to make certain of the length and that the dang bracket had not warped in all its snaking around the last four times I built this slide. Also, I was not sure I wanted to do all this work today. (I need to use this horn tomorrow morning for three quintet performances.) So that much-hated bracket is still soldered on the slide in its original position (underneath — the valve section is flipped over in this photo) and the slide, as is, moves *acceptably* well (yet I am unhappy with it). I know I can make it much better if I get that bracket off and rebuild it one final, heroic, stupendous time. (Heh…) So I was in the process of convincing myself to take the valve section outside, disassemble the slide, and redo the whole mess minus the stupid bracket. This ended up going *very* well and the slide works beautifully now. Then I soldered the bracket on at its new location, which you will see two photos down from this one.


I silver soldered the "T" and cleaned it up with the pickle and buffer. Then I checked the fit, marked it, and went back outside to silver solder the long arm. Before I cleaned that up I decided to go ahead and drill/tap the end and confirm that the linkage rod will clear everything with the lever at this length. I am glad I did because there were two issues. I ended up just bending the thing a bit and that solved everything. Necessity is a mother.


Everything lines up as I want. I am happy with this. Time to figure out a platen. I can make one from nickel silver bar stock, but that would take a lot of time, plus, that Kurath platen is weird at the angle he set it up, but rotated 90º it might be quite comfy under my thumb. I may try that. The issue is that I do not want to make anything I do non-reversible. Cutting up that horrible lever and… you know what? Screw it. I will *NEVER* want to use that terrible, old lever again. CHOP IT UP, BABY!


GAH! UGLY! Time for a bath in the nice vinegar bucket. That will clean off all that silver solder flux "glass" and get this part prepped for the buffer.


Et VOILA! I now have a new 5th thumb lever!


The platen is silver soldered at two contact points, so it ought to be plenty strong.


This is the stub of nickel silver rod I will drill, tap, cut, and then graft onto the stop arm, as well as the drill and tap I will use. I have to do this because the original one is set up to be a "puller" linkage and the pivot point is (as it ought to be) the stop-bar itself. I am building a "pusher" system, and to avoid something stupid like replacing the valve I have to move the pivot point 180º counter to the stop-bar on the component. This is how I will do that.


I drilled and tapped the stub of nickel silver rod so that it would accept the screw already in use. Screws are not free and a nice shoulder screw that fits with this Unibal link would be hard to find at Ace or HD. Reusing what I have is the better idea.


The finished stop arm. (Yeah, so I forgot to take a pic of it after the pickle bath and buffing. Watch the video. You can see it there. And NO, it is not off-center. The stub is sticking out toward the camera more than the other side — for clearance — so it looks like it is not attached correctly. It is, I assure you.)

[bloke]

<sidebar>
WITH APOLOGIES, BUT I COULDN'T THINK OF WHERE ELSE TO PUT IT.

Per a reply of mine (re: using mis-matched (round flange) brace feet on a mostly-diamond-feet-braces tuba)

Here are my decisions to use round flanges on the compact Holton B-flat...
- The only logical place to locate either one was on this (same) smooth convex bow connector/ferrule.
- I selected two different sizes, based on my evaluation of the importance of their jobs:
> The one supporting the inner/lower bow (that bow wasn't moving anyway).
> The one supporting the main slide (and keeping it perfectly aligned - well...a larger-gauge brace).

We all make decisions based on how we individually weigh problems/situations, and how much we weigh the visual and the practical.
(I always put a tremendous amount of weight on the visual, but - in these instances - the practical overruled the visual in two different ways - style and magnitude.)



<sidebar>