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Referring specifically to the internal moving cylindrical parts of the valve, how is the valve made generally?



I imagine that a brass blank is put on a lathe and the valve is then cut to shape before the channels are drilled into the sides. Even more specifically is the blank cut as a single piece (and a lot of brass is lost in the process) or is the wider valve body and the spindle cut separately in order to save material, and then somehow married and fused together?

Interesting question -- I've always believed it to be one piece, similar to how a one-piece mouthpiece is lathed from a single block of metal. Just my guess, since I've never hear of problems with the spindles coming off of the valves (or anything like that).

Also, I've always figured that any of the removed metal isn't really "waste" (like trash), because it can be recycled and melted down into usable metal again. I mean, you would certainly want to minimize it, but it's not a total loss.

Read the description (and see a picture) of the Kanstul lightweight rotor construction here - http://www.hornguys.com/basstbn1662.php
I think most other rotors I've seen look like a single piece of milled brass. Here's a good example pic (in a tubenet post) - viewtopic.php?f=2&t=49037#p423149. (I'm not sure how the cutaway happens like that if it's not a single piece.)

KiltieTuba wrote:There's a thread on here or on Oberloh's website that shows how rotary valves are made.

Here it is - http://www.oberloh.com/gallery/rotaryva ... onpage.htm

NCSUSousa wrote:

KiltieTuba wrote:There's a thread on here or on Oberloh's website that shows how rotary valves are made.

Here it is - http://www.oberloh.com/gallery/rotaryva ... onpage.htm

I'm always amazed at this stuff... to me, THIS is why tubas are (and should be!) expensive.

Truly excellent. Thanks for links.

I have a couple of antique instruments where the rotary valves are actually built up like piston valves. Less rotating weight.

bort wrote:I'm always amazed at this stuff...

Me too - I mean, why don't they just make them out of plastic?

(Yes, I know about HB)

Not a specific answer to your question, but interesting: http://youtu.be/NQIP53NEBIY

bloke wrote:I remember some 1970's Czech-made hollow valves. Those were very lightweight and worked very well. I don't know why they were discontinued.

Hey, I wonder if you could take a rotor like that and fill the hollow portion with a lightweight plastic, to make a composite rotor???

(So what was supposed to be the advantage of a composite rotor over a hollow one?? Obviously didn't turn out so well.)

Most rotors are solid, but Mr. Oberloh's appear to be hollow, like the old Amatis.
That seems like a lot more work, which may by why the hollow rotors are not found in newer instruments. I wonder if it also explains why student-model rotary tubas are now less expensive than piston models. For schools it seems like a false economy.

Modern rotors are typically machined from solid rod material on a four axis cnc milling machine. Some manufacturers have custom made milling machines set up for just making rotors. I have seen old cast rotor blanks that were made to be finished thru the old mechanical milling process but thats probably not very economical in this day and age with the time saving technology available.

D.C. Oberloh
Oberloh Woodwind and Brass Works
http://www.oberloh.com" target="_blank