The 6th lever is a real doozie, but it will work great once I have all the angles correctly dialed in. However, this rod is junk. I ruined it.
Once I bent a nice copy of the wire mockup link arm I realized that it actually was not the right shape. It took me several re-bendings to realize that 1.) I was not going to get it right using that method, and 2.) I was mangling the nickel silver rod. Once I allowed myself to accept that the rod was FUBARed I was able to use it to make a much better mockup, and that allowed me to see that it would have to be a two-piece rod to work as needed. No way around it. I have the long, central section locked to the piston set via two "pillow blocks" so it will not be able to flex to the side the slight bit needed to allow the stop arm to go past the stem, as that action does not actually have a straight path — it is a very shallow semicircle. To prevent the long, convoluted rod from flopping around and making all sorts of racket it has to be secured so that it can *only* travel up and down, and that precludes the action around the valve stem.
Solution: The short bit with the Minibal link on the end has to be a separate part, free to rotate as needed. Where the 90º angle occurs will be a wafer of .25" NS brazed onto the end of the long rod, which will be drilled and tapped like the stop arm itself. The rod needed for this bit is 7 mm of threads on both ends @ M3x0.5 with an 8 or 9 mm length between the two Minibal links. This will work very well. (I have made stuff like this in the past. It is a major PITA but if done right it works really well and is not slow or heavy-feeling.)
So in the pic, the red circles are where the pillow blocks will live on casings 2 and 4, and the rod will ride in them for alignment. The blue ends are the .25" wafers that will be tapped for the Minibal screws. The lower end will connect directly to the 6th lever via a Minibal on the blue spot.
I tried to make this short rod twice and this was the best I could manage. I need a lathe. This would have taken me like 15 minutes to make and it would have been exactly what I need. Note the lack of threads? Well, that M3x0.5 threading die took a walk on me. I have one on order and it will be here on Wednesday.
Why am I cutting down the rod rather than center-drilling and tapping the end for some all-thread rod? I need a lathe for that, too. My drill press is suboptimal in just about every category by which one would judge a drill press.
I will have a lathe by Christmas, though — I hope. My situation right now had me almost pulling the trigger on a lathe two months ago, and then the bottom dropped out on us again, and all that savings is burnt through, so I am starting over again. I will get it, though.
My solution for the short rod, since I have to buy two ridiculously expensive Minibal links anyway, is to buy the short arm kit from Instrument Innovations, which includes two Minibal links of the right size, two screws, and a nice, stainless steel connecting rod of 1.5", 1", or .5" (not including the threaded ends) and have him make the rod to the length I need. It is actually a little cheaper to do it this way than to do it myself, which is something that only occasionally happens.
So I now have the exact shape (torturous as it may be) for the long rod and an adequate solution for the short rod. Now I have to bend up my two levers so they do what I need them to do. I might have to destroy my nice 1st slide braze with the lever rack on it to change some things. This has been a genuine prototyping experience, with me having to do, re-do, and re-re-do my doo-doo to get it right. I have learned a lot, and the final product will be very nice. But it is costing me more than I had anticipated.
My final "final solution" is to eventually pick up two more valves, customized by Miraphone, so that they BOTH include ALL the things I need to make this work nicely. One day when I make that order, the levers will simply be two long, straight rods that run parallel on the same side of the pistons. Until then, I have to make do with what I ordered, despite my realizing that it was not really what I would need.
Again, prototyping means constant changes to plans as things are discovered. I now understand why it takes so long for tuba designs to move from the test phase with a solder-covered demo horn at TMEA until it is finally available for sale. Man, this it time-consuming work! But I get a kick out of it, to be sure.
The little, purple arrow shows how the end of this convoluted link arm has to move outside of what the red circles will allow. So that end bit has to be a separate rod that can pivot as needed. "It mocks me."
Despite the way the lighting makes the ends look swelled like little bats, they are actually filed pretty straight and even. Doing this work was a massive PITA, and I had to do it a few times to get it just so. And it is still UGLY work. So this will be replaced by the little assembly from Instrument Innovations.
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