"German Silver" Pistons

[ThomasDodd]

I think in either case, sleeves in the casing would be best. Much easier to replace the sleeve than to plate a piston, and rehone it.

It never fails to amuse me when discussion takes place on how repairs should be best be performed and how a straight forward repair can be turned into the most difficult and complex of processes. We Repair technicians have been successfully repairing and rebuilding valves (rotor and piston) for a long time.

I'm sure you guys do the best with what you have. And what people will spend.
Lack of strandrdization and poor parts availibility is and issue too.

My idea was a fairly thin sleeve, that wears, so that the piston, with a very hard plating, has nearly no wear. like 0.001" for ever 0.010" on the sleeve. This sleeve is a stock part. The ports are already drilled. It's not a comple cylinder, but split to form the keyway. It's larger than the casing, and compresses(like compression rings on a piston) when presses in. You line up the way and the edges with a long bar in the way while pressing the casing. The sleeve is shorter than the casing, and sits flush at the top, and has a 0.050-0.100" space at the bottom to make removal less error prone. Then a quick hone on the inner surface of the sleeve for the desired fit.

I'm just not sure if it need to be more securly fixed in the casing, or if the press fit would be enough to hold it still. Solder would make it difficult to remove. Maybe some sort of pin?

No machinging of parts. The whole job takes about 30 minutes per valve. Gets done every few (3-4) years, and cost about $50 per valve. Cheaper than the current methods (just replating the valves is like $40 each, without the honing and casing clean up), but done more often, so it brings the repair guys more work.

Only problem is parts supply. I don't know what the manufacturers are like in this area, or the likelyhood of a 3rd party source. When parts are not available, it can be convert to the old replating methods. This would be something for the big manufacturers and long lived valve body designs.

[Daniel C. Oberloh]

Interesting idea but no sell. I know a little about this kind of stuff and I can already see that this way of going about it is loaded with pitfalls and structural problems regarding the sleeve.

My idea was a fairly thin sleeve, that wears, so that the piston, with a very hard plating, has nearly no wear. like 0.001" for every 0.010" on the sleeve.

The piston tolerance in my rebuilt valve is .00025" +/- once they are fitted. Have you ever machined or drawn something that thin? .001" is half the thickness of a human hair. Simple idea to have someone else supply it as long as the "someone else" is not you. Think about it, fabrication of a ton of sizes and configurations of sleeves that will distort when pressed into a cylinder. The tooling costs and stocking something that is not needed makes it a not so attractive business proposition. If the ports are pre drilled the ultra-thin, slit tube with half a dozen holes punched in it will distort.

This sleeve is a stock part. The ports are already drilled. It's not a complet cylinder, but split to form the keyway. It's larger than the casing, and compresses(like compression rings on a piston) when presses in. You line up the way and the edges with a long bar in the way while pressing the casing

Stock part?!!! Your process has more work to it then you know. Picturing a very thin cylinder made of ? with a pre-cut slit for the key guide, that by the way will compress when inserted eliminating the integrity of the cylinder and distorts its bore once in place. Also, once inserted, guide way is compressed and that allows for give and will keep it from obtaining a snug fit . The ports will have to be an exact fit for one of how many different horns? Once you have your sleeve, what will you do? Make room for it in the casing by removing how much metal? How you going to do that? Once you got it in, you are going to hone it? reaming and honing are machining processes. Honing machines are expensive, I know as I have written the check. Few shops have this kind of equipment and know how to use it. I can go on and on and on but I have a rehearsal to attend so I will leave it there.


Daniel C. "who feels we have figured the best way to rebuild and maintain valves without re-inventing the wheel" Oberloh

[ThomasDodd]

My idea was a fairly thin sleeve, that wears, so that the piston, with a very hard plating, has nearly no wear. like 0.001" for every 0.010" on the sleeve.

The piston tolerance in my rebuilt valve is .00025" +/- once they are fitted. Have you ever machined or drawn something that thin?

My numbers were just to illustrate. The thickness of the sleve is determined by strength requirements. Maybe 0.050', maybe 0.100", it'd take some experimentation.Find something that presses in snug abd doesn't deform and loosen.

Think about it, fabrication of a ton of sizes and configurations of sleeves that will distort when pressed into a cylinder. The tooling costs and stocking something that is not needed makes it a not so attractive business proposition. If the ports are pre drilled the ultra-thin, slit tube with half a dozen holes punched in it will distort.

Not a ton of sizes. How many different bores are used today by a given manufacturer? Some standardization is needed. For a give horn bore, only a few piston sizes and prt layouts make sense. Whether the industry is there yet is another question. And this is something for new horns. Retrofitting to old horns would only make snse if the port layout, port bore, and piston bore matched, and the casing wall is thick enough.

Once you have your sleeve, what will you do? Make room for it in the casing by removing how much metal? How you going to do that? Once you got it in, you are going to hone it? reaming and honing are machining processes.

New horns would have a klarger casing to allow for the sleeve. Again, retrofitting isn't likely. As to honing the final cylinder, something like a brake cylinder hone. Runs on a standard hand drill/ press. No reaming should be needed.

[ThomasDodd]

I once had what I thought was a completely original idea about performing a specific task. I did some additional research and discovered that my idea had been discussed in the relevant literature in 1931 - they just didn't have the technology to pull it off.

Do they have the technology do do it now? It wouldn't be the first time an idea was ahead of it's time, an only became practical later.

This taught me that there are actually very few original ideas. I'm assuming that if there were a much better way to treat valves AND it could be done without increasing the cost of a horn through the roof, the engineers at the music instrument manufacturing companies would already be doing it.

There are plenty of original ideas. You give the engineers at the companies too much credit. Often they won't look at something way out there. And even if they did, getting management to buy in is even harder. Companies suffer group think problems. They have trouble changeing the way things have always been done.

[Rick Denney]

There are plenty of original ideas.

The difference between engineers and artists is that the latter are interested in creativity and imaginativeness first and meeting requirements second, while engineers are interested in meeting requirements first and foremost and use just enough imagination and creativity to achieve that result.

This is not group-think or being dull, but rather designing as little as possible to accomplish the objective.

Piston valves have two moving parts that are honed to match each other--the casing and the piston. They do not have a problem with longevity unless abused. They are user maintainable. Their lubrication requirements are simple. They are easy to make and repair (compared to most engineered parts that must be reasonably air-tight at low pressures). Any variation on the design is more complicated and more expensive, and still requires precision construction. And the alternatives (including your sleeve design) would require heavier casings (so they could be machined precisely and so they could be expected to hold their shape in a dangerous world--otherwise the sleeves would be distorted on installation).

The only problem with pistons is that renewing them requires a simple plating process and hand fitting, and thus requires an expert. Next time you rebuild a car engine, think about that (it requires an even higher level of expertise to achieve even factory production standards). Considering that the vast majority of piston-valve instruments will fall into disuse or be destroyed before the pistons wear out, this problem isn't worth spending a nickel to fix. Those of us who try to make old instruments playable can still do so, and can still spend less even after having done so.

Rick "recognizing some imaginative designs that nevertheless failed, including the plastic valves from no less than Hirsbrunner" Denney

[ThomasDodd]

There are plenty of original ideas.

The difference between engineers and artists is that the latter are interested in creativity and imaginativeness first and meeting requirements second, while engineers are interested in meeting requirements first and foremost and use just enough imagination and creativity to achieve that result.

This is not group-think or being dull, but rather designing as little as possible to accomplish the objective.

As an engineer myself, it wasn't ment as a slam on all. Group think happens a lot. I've seen it. It takes an outsider to move thing in a new direction. And I have seen management take the "we have always done it this way" stance to new ideas.

Place I once worked, new versions of products, now using surface mount devices. Engineer puts in a good op-amp circuit, instead of the single tranistor design used in all the old through hole designs. Management say do it the old way, to save $1 on a product that sells for $100+. They build hundreds, and ordered 1000+ PCBs. Problem is the SMT version of that transistor isn't strong enough and the aoudio level was too low. Product got lots of returns, and few sales later as word spread.

A few years later management agrees to a redesign with the op-amp. Product has a bad name, still sells poorly, and $1000 wasted.

[Rick Denney]

As an engineer myself, it wasn't ment as a slam on all. Group think happens a lot. I've seen it. It takes an outsider to move thing in a new direction. And I have seen management take the "we have always done it this way" stance to new ideas.

I find the cure for this to be a genuine application of a requirements process, rather than the lip-service most engineers give to requirements. Starting with the design and then justifying it is not a requirements-led process, nor is, as you say, relying on tradition without evaluating it against requirements.

Most thorny engineering challenges I face become pretty easy when the needs and requirements are made clear.

Rick "with hard-won experience in standards committees" Denney