homegrown piston repair

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Dan Schultz
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Post by Dan Schultz »

Conventional silver plating is not thick enough to be of help for loose pistons. Pistons are usually heavy plated with copper to fill the pits and make the piston physical bigger, then ground to size, and then hard-nickel plated (not silver plated). Just applying silver to the pistons won't do much good but won't really damage anything, either. Have fun!
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Chuck(G)
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Post by Chuck(G) »

TubaTinker wrote:Conventional silver plating is not thick enough to be of help for loose pistons.
Dan's got it right--go to

http://www.caswellplating.com

and get yourself a copper plating kit. Note that Caswell also offers nickel plating kits if you've a yen to add that to the job.
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Philip Jensen
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Post by Philip Jensen »

Henry,

I've got an old King baritone missing a 4th valve and have been keeping my eye out for a replacement. On my horn the 4th valve is actually shorter than the others. Is there any chance your valve might fit. There is a picture of my horn at the bottom of my web page (there is a link if you click on my profile).

Rather than replating all the valves, sell me the 4th and then besides playing around with plating the other three you can do some added surgery to remove the 4th valve assembly, wouldn't that be a lot more fun! :lol:

Philip
Miraphone Norwegian Star Eb
King 4V BBb ~1913
Holton 4V Eb 1920
Holton 3V Eb 1930
dave
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moglice

Post by dave »

I keep waiting for someone to adapt moglice or a similar product to brass instrument (piston) repair. For a project like this a castable epoxy based product with good wear and sliding characteristics would be ideal.

Moglice gets used to rebuild machine tools back to original tolerances all the time, including repair of hard-to-manufacture parts like lathe half-nuts.

-Dave
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Rick Denney
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Re: moglice

Post by Rick Denney »

dave wrote:I keep waiting for someone to adapt moglice or a similar product to brass instrument (piston) repair. For a project like this a castable epoxy based product with good wear and sliding characteristics would be ideal.

Moglice gets used to rebuild machine tools back to original tolerances all the time, including repair of hard-to-manufacture parts like lathe half-nuts.

-Dave
I've never heard of the stuff, so I'll ask: What are its thermal expansion characteristics? That has dust-binned the use of plastics for valves on more than one occasion.

Rick "recalling the plastic Hirsbrunner valves that worked fine on cool days" Denney
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Re: moglice

Post by Chuck(G) »

Rick Denney wrote:I've never heard of the stuff, so I'll ask: What are its thermal expansion characteristics? That has dust-binned the use of plastics for valves on more than one occasion.
Moglice has been around for awhile; it's basically a resin with lubricant additives (moly disulfide, I think) and fillers. It's used for replicating low-friction parts.

However, I wonder if the stuff is any good (i.e. will it flake off?) at thicknesses of only a couple of thousandths.
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Post by Chuck(G) »

DeWitt Machinery is the exclusive distributor of Moglice in the USA. See their web site at:

http://www.moglice.com/

You might want to talk to them--I believe that the stuff requires some sort of keyed surface for good adhesion.
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moglice

Post by dave »

Chuck is correct, the surface that the moglice is applied to must be rough, and the thickness of the moglice is usually .1" or greater. It might work ok for thin coatings, you would have to contact the manufacturer and ask, but my guess is no.

Most likely you would need to turn down the piston, fill the ports with wax on both the valve and casing, align the valve with a fixture to hold it centered, apply a release agent to the casing, then fill the void with moglice, etc.

Moglice has excellent durability; it is used for rebuilding machine parts that take quite a bit of hard use, to original accuracy, and it lasts quite well. There are a number of other products that are used for similar applications. For example, sheets of turcite are epoxied on to worn sliding ways of machines, after grinding the ways flat and providing enough clearance that the turcite will restore the original geometry. The company that makes Turcite has products for restoring round as well as flat surfaces.

-Dave
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Re: Problems probably outweigh benefits

Post by ThomasDodd »

Henry wrote: So in the end while I can certainly see using the stuff for pits/ dings/ and spot repairs I can't see why you'd want to use it for redoing an entire piston.
Depends on cost and tools available.

Looking at the cost of a plating kit, then a compount to lap/hone with, and the time, I expect it be cheaper to send it out to be plated. If you do a lot of this, sure, but for a one horn valve job?

Now, Moglice looks interesting to me. Need to check the cost though. Still I can get a valve turned 0.100" (or more) smaller easily/cheaply. This stuff to rebuild the surface, and match the worn casing sounds great. No/little lapping or honing needed. Just use the release agent to set the clearance.And should be a lot faster too.

Maybe use a adjustable reamer or brake cylinder hone to resurface the casing first?

My real question is, how much clearance should there be between the valve and the casing? It need to be fairly loose I guess. But maybe a few thin layers would work well.

Time for a phone call I think.

-Thomas
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Moglice

Post by ThomasDodd »

Just talked to the Moglice distributor. Suggested using a non-silicon car/table/floor wax instead of their release agents. The smallest kit is 100g or 3 c.i. and I figure about 0.35 c.i. per valve. For $36 sounds like a good deal, about $4 per valve.

The biggest issue if gettiong the minimum thickness, which for the FL/P is listed at 0.030".

So , how thick is the casing wall and the piston. If I hone the casing out, can I cut that much off the piston? Need to find my micrometer, unless you guys have an idea of the average thickness of the piston wall.

-Thomas
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Re: Please

Post by ThomasDodd »

Henry wrote:. I just can't see how I'll get over the ports in the casing issue. The piston ports are no issue at all but I can't see how I'll be able to wind up with a perfectly coated piston that doesn't wind up fixed in place by moglice/compound in the case ports without major valve set dissassembly..... Unless I don't take advantage of the release agent molding effect in which case there's no real advantage to me...
Since paste wax work as a release agent, it cheap and easy to fill the pison ports, the key slot and the ports between casings. I Figure for the tubing out of the casing , to the lead pipe, bell, and the valve tubing itself, something fairly stiff first then wax over it. If it melts easily or disolves in water, removal and clean up should be a snap. Maybe clay or playdough. It won't be exposed to air long enough to dry.

Oh wait. I got it. Cookie Dough! ;)

-Thomas
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Re: Problems probably outweigh benefits

Post by Chuck(G) »

Henry wrote: (I chose silver- see original thread post- because its less subject to rampant corrosion in a piston application than copper but still very easy to fit in. .
Copper-only plated pistons have been around a long time. I recently worked on a Holton euphonium from the early 20's that had copper plated pistons--none showed any corrosion. I suspect that copper is no more prone to corroding in a piston valve than is the brass that forms the casing.

What I can recommend against is using zinc plating on a piston. This was one of those "it sounds good" ideas that I tried on an old euphonium with disastrous results. Zinc corrodes quite rapidly in a moist basic environment and the pistons would freeze in the casings overnight. I eventually just buffed the whole mess off and replated with copper with good results.

Before you launch off on replating the pistons however, peer down iinto the casings, particularly where the leadpipe enters the first valve. Most often, you'll see that the brass is pitted around that port and needs to be honed down a couple of thousandths to get a good smooth fit.

It might be instructive to plate a piston in brass, but I'd just rather send the parts out for plating.
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Dan Schultz
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Post by Dan Schultz »

I once considered sleeving a piston with thin-walled stainless steel tubing but put the idea aside when I couldn't locate 'just the right size' tubing. It just seems like everything that one can think of to try ends up being little more that just a 'tinker' experiment and always ends up costing more that conventional plating. There are some casting compounds that might be useful in replacing an entire piston. If you really want to tinker with something, get some of the new space-age casting compounds and just use your casing as a mold to make a new piston. Pieces of vinyl tubing could be used to simulate the piston ports and the casing could just be filled with casing material. When the material is cured, simply press the new casting out in the direction of the keyway. I haven't got time to mess with it. If you take it on please post your results here.
Dan Schultz
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Current 'stable'... Rudolf Meinl 5/4, Marzan (by Willson) euph, King 2341, Alphorn, and other strange stuff.
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Chuck(G)
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Post by Chuck(G) »

TubaTinker wrote:I once considered sleeving a piston with thin-walled stainless steel tubing but put the idea aside when I couldn't locate 'just the right size' tubing. .
Didn't/doesn't Amati build their cheap piston valves that way? Seems that I remember seeing a 3v Amati BBb with sleeved valves. Didn't help much, though--the valves still didn't seal worth beans.
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