Lever engineering question

[roweenie]

Hi everyone,

I'd like to improve the action of this 5th valve lever by shortening the throw by at least 1/3 (right now it seems as though the ratio is 1:1 from the lever to the valve).

Does any of you engineer-types have some ideas or advice on what I need to do? I'm stumped.....

Thanks all,

Bob

[Dan Schultz]

The biggest problem I see is that the lower arm (where the spherical connector is) really needs to be closer to 90 degrees to the linkage direction. Fix that first. That will shorten the throw. If that doesn't get you where you want... try extending the lever where the spherical connector is and moving the connector farther away from the spring saddle.

[roweenie]

Dan,

What you are suggesting is to make that lever more horizontal?

I can certainly try that, but I'm not sure I have enough room to lengthen that arm -

I'll try changing the first and see if that helps ---

Thanks,

Bob

[roweenie]

I moved the rear lever up some, and unfortunately the effect was only marginal

Bloke, I think you are onto something - I think the paddle lever is too long. I find the throw is shorter when my thumb sits farther in toward the valveset.

However, before I open that can of worms, I think I might monkey with the thumb ring first (as per your suggestion). An adjustable one would be cool, but I don't have the resources to build one at present.

I agree that 1:1 is probably best, but the rotary valve is so big (22 mm) that it takes quite a stroke to get to the end - but then again, the piston valve bore is pretty long at .750, so maybe it's for the best.

[NCSUSousa]

Hi everyone,
I'd like to improve the action of this 5th valve lever by shortening the throw by at least 1/3 (right now it seems as though the ratio is 1:1 from the lever to the valve).
Does any of you engineer-types have some ideas or advice on what I need to do? I'm stumped.....
Thanks all,
Bob

Bob,
Please keep in mind I am an engineer, but I am NOT a tuba repair man. This is my opinion:
Shortening the 'throw' at the thumb end of the valve will significantly change the feel unless you also change the spring wrap to loosen the pressure to match.
Assuming you're not going to modify things at the rotor end (that could get tricky), you have 2 real options to change the throw that much:
Option 1 is to extend the length of either the lever connected to the pushrod.
Option 2 is to shorten the length of the finger lever.

Judging from your pictures, I don't think you can lengthen that arm enough to get a 1/3 reduction in throw without significant changes. That leaves changing the finger lever (the one that your thumb pushes). Shortening that will require additional changes to the thumb ring to put you back in position to reach the valve comfortably. It will also make it change feel more through the stroke of the valve.

There are other 'out of the box' options to pursue like completely scrapping the valve pushrod system you have (change to a pullrod?) or adding an intermediate lever on the pushrod system, but I have no idea if either would fit on your horn. Probably best explored by one of the tuba techs here while looking at your horn in person since they're more familiar with the availability of parts to get something like that done. There's not alot of distance from the thumbring to the rotor in your pics, so you may just have what you have (not many ways to change it).

If I really step back though, your question is one based on ergonomics. moving the thumb ring and the valve lever axis to a better position for your hand should make it feel much better without changing the throw distance (ideally it's a 1:1 ratio as described by the guys above).

Best of luck to you with this.

[roweenie]

NCSUSousa,

Thanks for your observations - it's good to get input from someone who knows the science behind this kind of stuff (unlike me!) I think I sometimes fall into the trap of thinking anything can be done with just a little elbow grease, even though the physics say otherwise....

It looks as though the next step is to reposition the thumb ring.

BTW, does any manufacturer make a NICE adjustable thumb ring (which is also readily available for purchace) that I could plant on the horn?

Thanks all,

Bob

[ghmerrill]

BTW, does any manufacturer make a NICE adjustable thumb ring (which is also readily available for purchace) that I could plant on the horn?

http://www.voigt-brass.de/gxshop/index. ... INGS.html&

Don't know about price. They don't seem to have fully implemented online ordering or price display. So prices of their component parts won't display. But there is a contact form on the site: http://www.voigt-brass.de/gxshop/shop_c ... php?coID=7. I'm sure you're only euros away.

[roweenie]

That thumbring looks awesome! Thanks for the link-

I've sent an email asking for details - I will report back when I have more info....

[roweenie]

I received the adjustable thumb ring from Voigt Brass yesterday.

Cost was: €29.81 for the part, and €20 for shipping. They were very easy to work with, and unusual for German manufacturers, they accepted Paypal!

Total shipping time, @ two weeks.

It is a really beautiful thing - however, if anyone decides to get one, go all the way and get the one with a swivel thumb ring. I didn't and wish I had.

[cambrook]

http://www.voigt-brass.de/gxshop/produc ... -ball.html

[roweenie]

P.S. - Moving the hole for the ball on the stop arm roughly 3/32" closer to the center changed the throw on the thumb lever from 3/4" to 9/16", with a negligible difference in response. That is a much more manageable distance for me. Along with the adjustable ring, I find it works much better...

Thanks for all the great suggestions!

Bob