Kurath/Willson F Tuba — Adding a 6th Valve

[Rick Denney]

This is really off topic, and - as this will derail for a couple of posts, I hope it gets right back on track...
I put two floor pegs on my cimbasso to avoid rotation, but - even though they are of a fairly stiff alloy of stainless steel according to specs compared to others, they still flex. I guess I'm going to have to go to something larger in diameter other than stainless steel, because (current are 8mm) something like 3/8 in diameter stainless steel would start getting really ridiculous, but I'm going need to find something that's within a diameter that's manageable yet not flexible. I'm guessing I'm going to need to go to something larger that is hollow with a fairly thick wall.

A tube will increase structural rigidity because of the increase in diameter. A tube of the same weight increases in stiffness geometrically with increases in diameter. A half-inch tube with a .065 wall thickness will let you press in 3/8" round stock for the end connections. McMaster sells it in 304 stainless in "medium-hard" condition, meaning it will be stronger than tubing used for plumbing purposes (which is supposed to be easy to bend--once). And I think it will deflect about 20% under the same load as if using a 5/16" solid rod of the same material, which is very roughly similar in weight.

By the way, the difference in stiffness between various alloys of steel (stainless or not) is quite small--probably unnoticeable compared to the difference between steels as a class and, say, brass or aluminum. Less-stiff stainless alloys like 304 have a stiffness modulus of 28 million psi, while carbon steel is only slightly greater at 29 million psi. Brass is 15, nickel-silver might be 18, and aluminum is about 10. Strength is a whole other thing. Stiffness controls how much it deflects under stress (officially, how much in strains in inches per inch, for a given stress in psi), while strength is the stress at which it becomes plastic and deforms permanently or ruptures (whichever comes first). Stainless is tough--it's gooey and the opposite of brittle--but non-stainless steel can be stronger (and more brittle). The range there can be as little as 30,000 psi and as high as over 200,000 psi. Tungsten carbide has twice the stiffness and density as steel, and can be orders of magnitude stronger. But it is brittle--it doesn't yield, it shatters.

Rick "uses mostly tungsten carbide tooling in the new lathe" Denney

[bloke]

If you have any ideas for a specific product and diameter sold by McMaster that is also not wildly expensive, I'm ready to look at it.



These rods extend about 8 inches below the bottom of the instrument, but are a couple of feet long each. I designed it that way thinking that I would sometimes be stuck right at the precipice of some steps playing this thing, but it hasn't happened yet, and maybe never.

I guess I could at least shorten them to 16 in each and redo the mounts. I wouldn't mind redoing the mounts anyway because I had two different ideas for them and they don't match each other.

[Rick Denney]

If you have any ideas for a specific product and diameter sold by McMaster that is also not wildly expensive, I'm ready to look at it.



These rods extend about 8 inches below the bottom of the instrument, but are a couple of feet long each. I designed it that way thinking that I would sometimes be stuck right at the precipice of some steps playing this thing, but it hasn't happened yet, and maybe never.

I guess I could at least shorten them to 16 in each and redo the mounts. I wouldn't mind redoing the mounts anyway because I had two different ideas for them and they don't match each other.

https://www.mcmaster.com/89495K725/

Rick "about 53 bucks for two 2-foot sections, plus shipping" Denney

[bloke]

@Rick Denney
Would it add any significant additional stiffness (since they're here - and if I don't mind the weight, as it rests on the floor) to glue (probably just glue the ends) the existing 8mm rods inside the 9+mm hollow tubes?

@Arturo Sandoval

...just curious if he's looking...

[Rick Denney]

@Rick Denney
Would it add any significant additional stiffness (since they're here - and if I don't mind the weight, as it rests on the floor) to glue (probably just glue the ends) the existing 8mm rods inside the 9+mm hollow tubes?

@Arturo Sandoval

...just curious if he's looking...

What are the dimensions of the outer tube? 9mm is 0.35"--I was thinking of tubing with a half inch OD and 0.37 ID.

McMaster's metric tubing with a 9mm ID is either 10mm or 15mm OD. 10mm is 3/8--won't move the needle much. 15mm is nearly 5/8--will move the needle a LOT, but it will be heavy.

Rick "Arturo told me we were diluting Wade's thread" Denney

[the elephant]

Arturo is over here at my place playing Quarters. He asked me to tell you "It's okay, guys!" and to follow this through to its natural conclusion.

Gotta go. The quarter is before me…

[the elephant]

I am finally back on this mess after a long stand of using this tuba at work. I have the next week completely off, then I get very busy again so this has to be finished by this time next week; whatever form this tuba is in at that time is what I have to go with until the end of this season in June.

Before I could do anything I had to Loctite the little guide block back onto the 1st casing. This time, with the valve machine off of the bugle, I could line everything up much better and then check clearances. It turns out I was *really* close, and I will go with what I have.

So, step one will be to connect the 6th lever to the upper end of the linkage rod. If I can do that I am nearly finished!

The next step is to tie the upper 5th lever into the existing 5th linkage rod. Fiddly but easy enough.

The next step will be to remove the 2nd slide and cut all four tubes by 3/8" and work out a stronger socket for the long pull rod on the slide crook.

After that is some "heat-and-pop" adjustments to a few detachable braces to make them line up perfectly. Then a very thorough search for any leaks. Then I have the final cleanup.

Certainly I can get my act together enough to finish this all in a week. Certainly.

However, I can't PRACTICE during this time, so I have EVEN MORE INCENTIVE TO GET CRACKING.


Here is a reminder of the linkage rod I made from 303 stainless steel. It is very weird and had to be very exactly bent or it would NOT WORK AT ALL. (Why do I do things like this to myself?)


The valve end is connected. The lever end is held on with a cable tie. The guide block has been affixed using blue Loctite, which is curing right now. Everything fits and lines up well, with tight-but-acceptable clearances.


The Minibal will not work here, so I have to build a hinge to keep this a single-plane joint.


This shift of a couple of inches to one side is what all the fuss was over. This made things *difficult*. The 303 stainless steel is perfect for this, having just enough resistance to flex in this shape with the needed OD and weight.


Can't this dang Loctite cure any faster? I need to get back to work!


It is tight, but the rod clears all the valve casings. The length of the rod that travels within the guide block will have some PTFE shrink tube to help keep it quiet. I have decided to extend that PTFE tubing down past the valves up to the next bend in the rod, in case there is enough slop to allow the rod to clack on the casing walls.


This is the "short arm" (<snicker> an old military slang term: FALL IN FOR SHORT ARM INSPECTION!) connection to the valve.

[the elephant]

This is going to work very well, I think…



By the way, Ginger says hey.

[arpthark]

Nice!

Requesting more Ginger plz

[the elephant]

I finalized what I want to do with the "short arm" design and am in the process of building the new one. The wind is at 100% kite-flying force right now, so silver brazing out there was a real bear.

I spent about two hours working out all the bits I would need to make and what stuff I had that could be recycled. The issue is that I have ONE size of hinge tube, but TWO sizes of drill rod. One is a matched set of hinge rods and tubes, and the other is Miraphone paddle rack axle rod, but I do not have the nice hinge tubing they use with it. I have to have shoulder screws that fit the tubing I choose to use, unless I want to make them using hinge rod with a thumb nut on the end. I am not sure these can be installed or removed with fingers where they will have to go. I think I will *have* to use a screwdriver.

So I am in a temporary SNAFU, but I can eventually order *exactly* what I need from McMaster-Carr. I just need things to work correctly right now, and I can do that. The time spent on this was to make a zero-work situation when the screws are finally ordered: just screw them in and done.

Anyway, I have to make the two tiny hinges on either end of the "short arm" very parallel and coplanar or the linkage will bind and drag. I could not figure out how to do this AND silver solder the three parts together. My soldering jig has all the precision of a 3rd-grade art project.

I decided to build this like a slide to ensure everything will play nicely together, so I whipped out the granite surface plate, the adjustable parallels, and my soldering gear. It came out perfect, too! I am quite pleased, despite the terrible wind. I have a nice, square, and true "U" shape with the bent arm as the base and the two hinges as the ends. They are about 3.5 inches long, and when they come out of the pickle to remove the brazing paste "glass" I can cut the tubes down to the 4 mm height I need.

I have to do something similar to the lever/rod connection this afternoon.

Photos later…

[arpthark]

I am going to eventually bug you to make a Pictoral Toobuh Repair Part Glossary for Noobs.

Hinge tube?

Drill rod?

Axle rod?

I am sure if I saw it I would immediately know what you are talking about, but words are hard sometimes.

[the elephant]

[the elephant]

Okay, time for some truth.

The end of the video shows how off-plumb the factory hole is. I supposed that with high-deflection Minibal heim joints if the screw hole is not straight it does not matter, so their standard for that has come down over time. Well, with my linkage it matters a LOT. It does not work when installed.



I will fill the hole with silver solder, and then redrill it using my drill press, which ought to bring the hole into alignment with the valve stem.

The old "S" arm system had to be more or less spot on. I have a new-style (half-round stem shape) stop arm for the S arm system and I may use it instead. But I will have to hack on it a lot to make it work. (I have done this a lot in years past, so no issues, just wasted time.)

After that has been fixed I can address the other issues with the length and offset. It is different than the first one I made (with the Minibl on one end), which was made incorrectly by me, but it sort of worked whereas this new one does not. Some bending ought to fix everything, though.

I'm out. Time to take the wife out for a Valentine's Day supper!

[the elephant]

Okay, so the crooked screw *is* the problem. I have a solution that I will try tomorrow.

Thanks for reading!

[bloke]

Got spare screws? I hope. Let me know.

No need to reply

[the elephant]

Let me know.

Okay.

No need to reply

Oh, Okay.

[the elephant]

Okay, so there were two issues and they have been figured out. Now it works.

The stop arms that Miraphone makes today for the Minibal system are frequently poorly drilled. Since the tiny heim joints have so much deflection built into them, and the actual, needed deflection is only a small amount, having the hold drilled into the stop arm no longer has to be in alignment with the valve stem; it just doesn't matter.

The design of the S arm stop arm requires the stem hole and the stop arm screw hole to be dead-on accurate or the parts will bind when rotation causes them to move into different planes. These parts are very accurately made. The stop arm post is lined up with the stop arm body. The valve stem hole is drilled accurately through the center, and then the screw hole for the long shoulder screw that captures the S arm is correctly lined up with the valve stem.

I had never considered how much EASIER it is to make the new stop arm versus the old style one. Anyway, since the screw that retains the Minibal to the stop arm no longer has to be perfectly straight… it seems that it is rarely perfectly straight. Disappointing, but not having to worry about that probably saves money or time or both.

Once I had a new stop arm with an accurately drilled hole for my short arm screw (well, as accurate as I can get with my Mk I Eyecrometer) I could mount this beastie up and see what else was wrong.

And that turned out to be the guide block. I had inadvertently Loctite-ed it a quarter of an inch too close to the valve cap. Once I had pried it loose and moved it the lever worked very nicely. It is not perfect, but I know what to tinker with to adjust it.

I bought some nicer screws from McMaster-Carr, so this stuff will not look quite this sketchy in the end.

Check out how crooked the holes in the two now-ruined stop arms are from the factory in the video below. (I just opened up the holes, they were crooked when I got the parts. I will silver solder them closed, re-drill and tap for the Miniball screws, and put them back where I got them. No loss other than time.)

NOTE: I refer to the stop arm I will be using as a "new version" of the old style S arm stop arm. By that, I mean that the stem hole has the currently-used "half-round" hole rather than the old "house-shaped" hole.

[arpthark]

Me: Google search "heim joint"

Also me: "wow, these all look like Minibal linkages!"

[the elephant]

Preview of the levers…

[the elephant]

Close, but no cigar…