Sleeving Valves and Other Heroic Measures
Most old brass instruments are not worth the cost of labor to repair or restore them, but on the high end of the spectrum, there are some so rare and desirable, that they find an owner willing to spend what is necessary to bring them back from the brink. I've covered a few other such restorations, such as the Eisenbrandt double cornet,Teltow cornet and other one of a kind relics, but in this case an almost identical instrument exists to know the design of the missing parts.
These are Eb tubas made by Graves & Co. in Boston in the mid to late 1850s. The complete example in the second photo belongs to Mark Elrod and the other is in the collection of Steve Ward. It's flattering to know that Steve thinks that I can repair or reproduce anything, but the expense of the many hours involved in this project exceeds the sensibilities of most collectors.
The third photo on the right shows some of the steps involved in reproducing the missing valve casings, but the subject of this page is the much simpler process of installing a sleeve on a valve to restore its intended function. Notice that one knuckle is also missing from the second valve casing. This was replaced with one newly made before proceeding with the repair of the rotor.
It is a matter of course that many valve rotors or pistons will need to be built up with plating and refit to the casing to make them air tight once again, but when the amount of build up exceeds .010", the plater must build up plating and hone several times before achieving this result. In rotary valves, this is even more labor intensive, necessitating repeatedly hand lapping the increasingly rough build up of plating. A fairly simple solution, taught to me by the great Los Angeles repairman from my youth, Larry Minick, is to solder a sleeve on to the valve to make up the needed dimension. In my experience, this is most often needed in the case of piston valves that have been dented and otherwise damaged well beyond normal wear and tear, but I have also used this technique on rotary valves, as shown here.
At some point in the usage of this tuba, the second valve rotor must have been lost or badly damaged and the solution was to put the fourth rotor in its place and remove the entire fourth valve and related tubing. It probably didn't play very well at that point, since the replacement rotor was undersize compared with the intact first valve which was still acceptably tight as I found it.
The first step in this process is to carefully examine and measure both the rotor and casing to determine what needs to be done. The bearings were fitting well, but the clearance between the rotor and casing ranged from .007" to over .012", the variance being in the out of round casing and a low spot in the rotor. Even though the valve body and bearings were fairly concentric, I decided to machine the rotor body in order to make the wall thickness of the sleeve enough for reliable rigidity. This involved making accurately fitting brass collets or adapters as seen in the fourth and fifth photos. One of these has a split in it to clamp the stem in the lathe collet and the other is long enough to engage the tailstock center. I carefully checked that the valve body and bearing were centered using a dial indicator.
After machining the body to the desired diameter, I made a sleeve with a good slip fit for soldering and the outside diameter about .01" larger than the finished dimension. As I slid this over the rotor, I inserted steel ball bearings onto each port for ease of locating the holes. After soldering, I used a magnet to locate where the holes need to be cut in the sleeve. The result is shown in the tenth photo. Using the same brass collets, I machined the sleeve to a slight taper matching that of the casing.
Because I want to lap this into the casing, I made it about .003" oversize. If the casing was in better condition, I would have made this only .001" or less. The eleventh photo shows the rotor after machining, but before lapping. If this were a piston valve, it is best to hone it to size at this point. The next photo shows the valve after the final lapping along with the rest of the valve parts, original and newly made. You can see that the first valve needed no lapping at all. The last photo shows the valve assembly assembled with original second valve lever and three newly made to match.
The rest of the photos show the same process on a piston valve. In this case, the piston was a replacement from another cornet that had the exact port positions as the one being restored, but was about .010" undersize. This could be built up with plating, but this is an excessive amount. While the ports could be masked to eliminate the build up inside them, I prefer not to mask port in antiques. The extra abrasive cleaning of the ports after plating and scraping the edges could cause it to leak at that point.
Photo 15 shows that I've made brass plugs for each end. The long, narrow one, fits snugly into the spring barrel so that it won't collapse when gripped in a collet. The other will be soldered into the bottom of the piston and then center drilled as seen in photo 16. After determining how much wall thickness I can safely remove and find a nickel silver tube for the sleeve, I mount it in the lathe (17) and machine to fit the sleeve (18).
As I slide the sleeve on the piston, I place a steel ball bearing in each port. The ball should be as large as will roll through the port. Using a strong and thin magnet, locate and mark the approximate center of each port (20), then cut the holes (21). I use a small jewelry type of hand grinder with a small abrasive wheel to start, a burr to open them further and finish, very carefully, with a scraper. Great care must be taken to avoid cutting into the port or piston wall. It may be necessary to add some solder, if the original piston had deep dents, causing gaps. This is then machined to a diameter that can easily be honed to size (22). If there is no honing machine available, it is much more difficult to achieve as good a fit. However, in most cases I would send out the entire piston valve section for plating and refitting. It will be an easier job for the plater, not having to build up the entire thickness with plating.
Even without plating or honing to size, with a well tuned lathe and very careful work, the piston can be machined close enough to lap into the piston and be an acceptable fit for playability.