Good afternoon followers. This week has been an exciting one here in the brass lab as we start to deal with pistons and casings. Issues with the pistons and casings can be very troublesome. With the tolerances of today's horns, the smallest dent can seriously inhibit the horn's ability to function. Valves easily get stuck and the horn no longer plays. This week we learn how to rectify some of the issues that cause this.
We start off this week with damaged bottom cap threads. You may recall that I had this issue on my project trumpet last semester, and I went about fixing this the same way. Using dent balls, I worked the bottom of the casing back to round. I then used the bottom cap, and the Ferree's thread burnisher to rework the threads that were damaged in the bend. After a little bit of chasing and working, the bottom cap threaded on like new.
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The next issue to deal with was dented casings. A small ping dent like this one may not look like much, but it was enough that that piston wouldn't move. To take this out, I first cleaned the casing to a nice shine with a brass brush and Scotch Brite. Using a ground casing mandrel, I hammered the dent down with a series of mallets and hammers ranging from leather-faced rawhide to stainless steel. After a little bit of working and a bit more cleaning, the dent was down and the piston was free.
We started getting into French Horns this week as well. My project horn is an Oxford double horn. It's a heavy junker that's missing a few parts and has more than a few dents. To get her prepped for dent work, I stripped her down and started cleaning. Like the trumpets, I began by pre-cleaning all of the slides, inside and out. I also disassembled the rotors and cleaned them. It all took a bath in simple-green solution for the gunk, and phosphoric acid for the corrosion. I learned that rotors can be particularly corroded in older horns, so after 4 baths in phosphoric acid I stepped it up to muriatic acid, which is diluted hydrochloric. A few rinses with that cleaned it right up. All of the bare brass got stabilized and she is now ready for some dent work.
The next issue to deal with was dented casings. A small ping dent like this one may not look like much, but it was enough that that piston wouldn't move. To take this out, I first cleaned the casing to a nice shine with a brass brush and Scotch Brite. Using a ground casing mandrel, I hammered the dent down with a series of mallets and hammers ranging from leather-faced rawhide to stainless steel. After a little bit of working and a bit more cleaning, the dent was down and the piston was free. 
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