PTFE valves

[joh_tuba]

I've been spending an unhealthy amount of time on this website: http://www.mcmaster.com/.

From my armchair vantage point it seems like someone with a decent lathe, drill press, and some skill could produce an all PTFE(teflon) rotor or piston valve.

PTFE rod and tube stock is available in an assortment of dimensions and would be an easy material to cut and drill to size. The only major roadblock that I see is bonding PTFE to itself. That might requiring a 'heat melt bond' a specialized adhesive or some sort of screw or pin solution. Connecting to the brass tubing of the tuba might require an o-ring connection.

This also assumes that the stock PTFE tubes and rods are manufactured to a tight enough tolerance to make a proper seal without significant re-machining.

Thoughts?

[Ben]

Thoughts:

PTFE milled in this fashion would be dense solid plastic, and have more mass than our current hollow pistons. Being a soft material, PTFE would also wear quickly if presented and sharp edges, or distorted surfaces (bent valve clusters).

I am not certain if the bonding issue would be much of a problem from a machining and production point of view, and the tolerances should not be to much of a problem - CNC machines cut to very high tolerances regardles the substance. I would be more concerned about thermal expansion coeficients of PTFE compared with brass.

[joh_tuba]

Ben,

You make good points. I was imagining both the casing and valves being made of PTFE in order to get around concerns over expansion coefficients.

A cursory google search for PTFE adhesives suggests that it's a thorny problem and attaching all the valve ports might be a real headache.

Regarding weight, that might actually be my biggest concern.. particularly for a piston valve. I once played a vintage york that had a reconstructed fourth valve in which the missing bits were molded from a teflon plastic material. The piston was NOTABLY heavier than a standard piston and despite the work being done by a very well respected and well known repairman the end result quite frankly sucked. It was a technically impressive accomplishment but nothing I would pay money for.

[Dan Schultz]

Folks have been 'fiddling' with plastic and composite pistons & rotors for quite a while and have not been able to 'whip' some of the problems that tend to be big surprises.

I spent many years with the design of plastic injection tooling and engineered plastics. The biggest problem as I see it is a phenomenon known as 'creep'. For lack of the right words to describe this... I defer to Wikipedia...

"Because of its chemical inertness, PTFE cannot be cross-linked like an elastomer. Therefore, it has no "memory" and is subject to creep. This is advantageous when used as a seal, because the material creeps a small amount to conform to the mating surface. However, to keep the seal from creeping too much, fillers are used, which can also improve wear resistance and reduce friction. Sometimes, metal springs apply continuous force to PTFE seals to give good contact, while permitting a beneficially low percentage of creep."

Therefore... I don't think pure PTFE is a good candidate for pistons and rotors. However... there may be some engineered plastics out there that might be worth a try. The problem there is that materials such as Valox and Fortran are hideously expensive and have faults of their own.

[TheBerlinerTuba]

Hallo,

Laetsch of Bremen, Germany machines their rotors from pure carbon rod(the casings are brass). In addition, the backing plate spindle is supported by a true roller bearing rather a typical bushing. This comes standard on their instruments and they offer a conversion kit for other brands. They have been doing this for some time now, and the valves seem to hold up just fine and don't stick(although repairing them would be difficult). I've tried a Bb Kaisertuba that was modified in this way and it was a significant improvement.

cheers
2165

[Dan Schultz]

Hallo,

Laetsch of Bremen, Germany machines their rotors from pure carbon rod(the casings are brass). In addition, the backing plate spindle is supported by a true roller bearing rather a typical bushing. ....

Awesome!

A few questions:

- Can you describe the manufacturing process for the 'carbon rod'? Is it similar to silicone carbide in hardness?
- As an engineer... I've always been taught to avoid using roller bearings in cases where the moving parts have a rotation of less than 360 degrees. The reasoning being that lubrication is not distributed on all the moving surfaces. Is lubrication required? ... or does the system simply rely on all of the surfaces being super-hard.
- How about the front bearing? Wear on the front bearing seems to be greater that the rear bearing.

[TheBerlinerTuba]

no problem, i'll answer as best i can although you should write laetzsch for the specifics.

Unfortunately I don't know how the carbon rod is formed. I believe it is much softer than silicon carbide. The end fitting of the valves required a bit of "chamfering" and a penknife was just fine so it was quite a malleable material. My only experience with silicon carbide was installing new brake rotors on my racebike;)

I don't know for sure, but I believe roller bearings were used because they distribute the load from the spindle more than say ball or caged ball bearings(more bearing surface area). Considering how light the rotors are, and how precisely everything is machined, i would say the bearings are not under much strain.

I seem to remember the guys at Laetzsch telling me to oil them, but the owner of the Kaiser rarely if ever, oiled his valves(daily orchester use 10+years), and they were very smooth and with strong compression. However if it was my tuba, I would probably oil them...

Only the backing plate had a bearing. The tapered spindle was like a normal rotary valve, ie.bushing

cheers
2165

[joh_tuba]

Bloke: I think you are right. A properly designed, nickel and brass stock nickel plated piston valve is probably as good as it will ever get in a piston design.

Honestly, my thoughts were leaning more towards rotor designs.

Even as I made my initial post I was talking myself out of the whole PTFE plastic idea, too many issues that negate any theoretical benefit.

The obvious fascination with a PTFE rotor is the self lubricating properties, but if it's constantly binding on itself and the material has too much mass to overcome inertia then what's the point?

2165: You anticipated my next thought! As tubatinker pointed out, there are other self-lubricating plastics available but all of them present problems. I don't have any experience with any of these other plastics but I'm sure he's right. With that in mind the only legitimate alternative to brass is a material that is chemically inert, offers a significant reduction in mass, and is both extremely rigid and doesn't expand and contract over a large temperature range so that you can keep the brass casings.

I now know of two german firms that have followed this line of thought and decided upon graphite: Meinlshmidt http://www.jm-gmbh.de/html/meinlschmidt_tuba.html and now Laetsch.

An extremely adventurous person could machine their own rotors with this: http://www.mcmaster.com/#graphite/=j1tdkn

I'm not convinced that there is anything particularly limiting about the standard brass bushings on a rotor(although I do think it's reasonable to have them designed so that they can be replaced with standard parts) but I'm intrigued by Laetsch's idea of roller bearings. I'd be curious how Laetsch has implemented their design.

[Dan Schultz]

Good ideas come from discussions like this. Keep it up!

[TheBerlinerTuba]

to joh_tuba,
don't be afraid go the whole way to try an idea. It's the only way you'll know if it has merit. If fact, even if it's a complete screw up, you'll still learn from the process and you might even find something new.

I have a Pt6p that i've had for 2 years now. While I like the horn, the stainless pistons are POS. Heavy, slow, and they feel cheap. I have a friend who is turning me some titanium valve stems and finger buttons. I am making new pistons myself out of nickel stock. Apparently, I'm not the only one aware of this problem:
http://www.jm-gmbh.de/html/meinlschmidt ... valve.html

to goodgigs: your life is your own. You only live once. If you make a set of carbon/roller bearing Allen valves that works, you got one customer already. B&S is saving money with their stainless valves, and in the end I'm the one who ends up paying...

cheers
2165

[Mark Horne]

The french horn manufacturer Finke has been successfully been building rotary valves with synthetic materials for some time now.
http://www.finkehorns.de/English/NewsVentil.html" target="_blank" target="_blank

I don't know the materials used, but their horns are light and play exceptionally well - equal to the best horns I've played anywhere. It appears that they have been able to address many of the concerns that have been brought up here.

[joh_tuba]

Thanks for the encouragement and links to manufacturers that have explored these options.

Studied various materials a bit more and am currently intrigued by alumina silicate ceramic: http://www.mcmaster.com/#standard-ceramic-rods/=j2iqp1



About 80% sure this is the material that the Christian Lindberg rotors are made of. I feel like those rotors move WAY too slow for tuba applications in large part because they have a LOT of surface area in contact with the casing. The top and bottom of the very large diameter rotor rest flush with the casing. The addition of thrust bearings would probably help a lot merely by solving that obvious design flaw.

Benefits of alumina silicate ceramic: corrosion resistant, easily machinable(even complicated shapes), less than 1/3 the density of brass(0.09lbs/in3 vs 0.303), porosity of 2 to 3%(I think that's probably good, right?), similar coefficient of expansion I think(0.0000016/F degree vs 0.0000112 for yellow brass).

I lack the engineering background to have any real clue but I'm enjoying the process.

Feedback from those with a clue(or not) welcomed.

[Dan Schultz]

I 're-made' a change valve for a double-belled euphonium once. Someone had tried to drive the piston out of the casing and literally sheared the bottom plug, ports, and top cap right out of the sleeve! I don't remember the make of the euph but the sleeve was stainless steel. Since I already had the piston sleeve... all I needed to do was reconstruct the port passages. Since this was the change valve... there were only two ports. I put rubber rod through the ports and filled the sleeve (piston shell) with a hard-resin casting compound. Weight wasn't much of a factor since this valve is only used to change from one bell to the other. The 'fix' worked great! I'm not recommending this as a way to make pistons but just offering it as 'food for thought'.

[joh_tuba]

I did a bit more Googling about and have more to report.

1) It is possible to nickel plate a ceramic. In theory you could build a fancy hair-brained piston or rotor and then nickel plate it to make it slick as snot in the casing. It could very well be the best of all possible theoretical worlds BUT I suspect that the final product would cost far more than any normal person would be willing to pay.

2) The MAW pistons mentioned previously in this thread and cited here: http://www.jm-gmbh.de/html/e_meinlschmi ... _valv.html Appearly to be designed by Martin A Wilk of Palmyra, IN. His site: http://www.mawvalve.com/ and the patent: http://www.google.com/patents/US8227677

Martin has received tremendous positive press on Tubenet over the years. I've sent a few emails and will report back what I learn.

I've started paying a lot more attention to piston design and construction lately. I'm a rotor guy and generally just haven't paid that much attention.

Which brings me to:
3) Comparing the weight and feel of an older Besson piston made with traditional thin walled brass tubing and nickel plated vs a modern stainless steel piston is a lesson in abject horror at what we now accept as a 'good' valve. Also took the time to check out the valves on an old York tuba recently.. same experience. Knowing what I know now.. it's really hard to imagine improving on a good nickel plated piston. Bloke... your reply at the top of this thread was dead on right. They got it right years ago. Honestly, we should all be revolting en mass at the current state of tuba pistons. They are genuinely awful compared to tubas of old.

Since any fancy nickel plated ceramic valve would be definition be solid rather than hollow like a traditional piston I can't imagine the weight difference being enough to justify the expense or effort. This experience has simultaneous killed by thoughts regarding plastic and ceramic pistons AND fueled my interest(for the first time ever) away from an improved rotor design and towards an improved and/or 'classic' piston valve.

Which leads me to:
4) If the MAW replacement pistons for MW big block valves are made of brass and nickel rather than stainless steel then anyone that can afford them should *really* seriously look into it. With a guy like Martin Wilk behind the design odds are good it is being done right. The ad copy reports that they are designed to "maintain the evenness and sonic qualities of a traditional rotor design". That combined with Martin's reputation is enough to pique my interest.

I'll report back when I learn more.