There are several civil war band reenactors in the area. They all play period correct horns. Old horns wear out. This particular beast had worn out stems on it's rotors. The original stop arms had steel pins instead of a brass rails as are found on modern rotors. The steel pins severely wore the alignment groves in the rotor stems. I considered replacing the stems on the rotors, However, I didn't want to cut into a 150 year old valve. So instead I decided to make up new stop arms.
I started with some stock turned down to the diameter of the old stop arms, 0.535''.
Next I made of the arm of the stop arm. I used an old sax key for stock material. Once I had the blanks shaped to sizes, I set them up in a tool holder on the lathe.
Using a #52 drill, I lined up the stock brass and drilled a hole. I then tapped it to a 2-56 thread.
In order to make a clean, solid, silver solder joint, I filled a bit of a dish into the stock.
Next step was to silver solder the arm onto the 0.535'' stock.
After cleaning off the flux and heat varnish, I chucked up the stop arm in the lathe and turned the part to length. I then drilled the holes. A #18 and a #4 bit were used.
From here, I lined up the new rail slot with the old stop arm's pin. I cut the slot with a jeweler's saw and a needle file.
Now I filed a peice of square stock into a new rail. Each one of them was fit perfectly to it's respective valve's groove.
Next step was to silver solder the rail onto the arm.
Last step was to file down the extra brass and buff it up. There also was little bit of cleanup needed on the inside of the arm, too.
I made up two more. Here are the old arms (above) and the new (below.)
The last thing to do was assemble and port the valves. This was done with a usb scope. These old valves have no witness marks.
Here is the horn all assembled and ready for the customer.
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