TubeNet

I need to build up two rotors oversize as part of a valve job. I made a series of laps in .001" increments to repair the casings (the laps are tapered and have a tapered stem, just like the rotors). The rotors will be turned on the lathe then lapped in place.

I checked with Anderson plating, and they don't do brass plating. I know they can do copper plating, so I may have them do that, but my preference would be brass just because it is what the rotors are made of. The local places that do brass plating don't understand the concept of plating to a thickness measured in thousandths of an inch...

I know about metal spraying, but I am not sure I trust the local outfits who do it not to ruin the rotor in the process. they normally deal with much larger repairs.

Opinions or suggestions?

-Dave

Why not have the rotors copper-plated, machine them to slightly undersize, then have Anderson plate a layer of nickel on top?

You could also give Atkinson horns a call down in Los Angeles and see what they think, as they do quite a bit of rotor refurbing.

Brass can be plated, but in all the cases I've seen, it was mostly for cosmetic purposes, not a machinable surface.

I thought about nickel plating too, but I have never seen a nickel-plated rotary valve, and I don't know if the surface properties are right for a rotary valve. I suspect that the nature of the seal of a rotary valve is slightly different than a piston valve. I don't think nickel wets as well as brass, which is part of the reason you oil pistons but don't oil rotary valves. Since I want to keep the new ground I am walking over as
well-defined as possible, my first preference is brass, then copper since
it is similar.

-Dave

Well, if you wanted to experiment on your own, you might look into this:

http://www.caswellplating.com/kits/brass.htm

They also have a brush-plating system for small items, but I suspect that the resulting coating is only microns thick.

dave wrote: I suspect that the nature of the seal of a rotary valve is slightly different than a piston valve. I don't think nickel wets as well as brass, which is part of the reason you oil pistons but don't oil rotary valves.

I'm no authority, but I believe you are correct. But since you'd have to machine the valves for a nickle coating, why not just go with brass and take the suckers down to where you need them?

I suppose I am an athority,
I do rotor rebuilding from time to time and though I use Anderson Silver Plating for decorative plate and structural plating on pistons, I keep rotor plating close to home. Brass plating is primarily for decorative finishes and is most commonly done on nickel plate over a copper strike on the sub-straight, it is also used for its surface lubrication characteristic in certain industrial applications. I and others rebuild rotor valves with copper and nickel. Your concerns about nickel are nothing to be worried about as it works great. Putting the rotor on a lathe and turning it after plate is a sure fire way to seriously screw it up. This is roughly how I go about it. First, I will refit the bearings both front and back. Once shields are fitted to the ends of the rotors to avoid excessive copper build up on the ends, the axles of the rotors are masked and I will have the platers put down about .00075'' (aprox. 20 minutes in the tank) thickness of copper, then hand lapp the rotor to its respective casing. The plating and lapping process is repeated two or three time. Once the rotor is well fitted it gets a 10-15 minute stretch in the nickel bath without guards or masking. final lapping should yield good results. I will use a high quality micrometer and get measurements from the rotors prior to plating so I can monitor the thickness throughout the process. I am guessing/hoping you know what you are getting yourself into. Good luck.

Daniel C. Oberloh


Oberloh Woodwind and Brass Works
Saving the world, one horn at a time...

www.oberloh.com

Daniel,

What grit of lapping compound do you use for the final lapping?

I think there are a lot of very good reasons for turning the rotors. I didn't go into this willy nilly, there was a bit of thinking involved. I hope your comment wasn't intended to stop discussion on this point.

My reasoning for turning the rotors is that
- rotors and casings are turned when new, then they are fitted together by lapping.
- using the rotor as the lap is not going to result in an even taper. Getting an even clearance will be harder than starting with close tolerance parts. It requires multiple re-platings, which for me means repeatedly sending the valves to Anderson and waiting for 2 wks. If the rotor is over-plated, it won't rest on the top bearing and will keep working its way down as it is lapped, with erosion of the top edge of the valve.
- by lapping the casing before having the rotor plated the clearance can be measured (using plastigage) and the amount of plating to add will be known.
- the laps were made using the same setup the plated rotors will use, have tapered bodies and the spindles are tapered to fit the bearings. The angle was determined by reference to the actual rotor. They are also taller than the rotors, so they won't create a step that affects the rotor's final fit. I made two of them that have a difference in dia. of .001", but by removing shims at the top of the lap I can decrease the clearance of the lap in an 8-1 ratio (shim thickness to clearance) to keep up with lapping, so there really is a continuous range of lap sizes.
- new laps in increasing diameters can be made as needed.
- If I make new bearing inserts, they will use the same setup on the lathe to bore the taper (the taper on the rotor body matches the taper on the valve spindles). I don't need to make new bearings, because the valves
didn't wear out, they had active corrosion when I got the horn.

-Dave

Dave,
Nah, I don't want to stop discussion. I just get a bit perplexed with what seems to me as reinventing of the wheel and curious as to why?

I use Cloverleaf 600 grit silicon carbide, grease base compound. I understand your reasoning to a degree but it seems to me that you are making a bigger production out of the process than is normally called for. Sort of like the idea on this forum of sleeving piston valves which (in my opinion) would be an insane amount of extra work in contrast to the plating and honing process that works great, is cost effective and can actually be performed. The typical procedure for rotor refitting is to lapp the rotor body not the bearings to the casing. Plating tends to build up on the ends of the rotor body, or should I say the sides/corners/edges unevenly. Not building them up to much at one time and lapping to fit works great unless you are working on a valve that is hamburger. Fitting the bearings prior to plating will center the rotor in the casing and not allow it to work itself further into the casing. The rotor and casing wall will even out during the lapping process. If what you are saying is that the casing is badly corroded and pitted with dezincafication, well that is another story. I myself don't have time to waste on those projects so I will call the valve maker and have them send out new valve assemblies. Its a cheaper and better way to go. Turning rotors and boring casings is going to remove a lot of metal and building it up with copper is going to be a pain in the butt that is still going to be done in many stages and it is still going to need to be lapped to fit. Like I said, I have done this before (many times) on tubas, french horns, trombones, etc. Take it at face value. Let me know how it works out. Good luck with the project.


Best regards,

Daniel C. Oberloh
Oberloh Woodwind and Brass Works
Seattle, WA
206.241.5767
www.oberloh.com