Inserting the brass piston liners
A great deal of handwork is involved in the proper construction of a trumpet piston. In this video you can see some of this during the insertion of the brass piston liners.
First, cutting a piece of nickel silver tubing to length and then drilling the proper holes creates the piston blank. Hole location is crucial to ensure both radial and linear alignment with the valve casing. The next step, shown here, is to insert the piston liners into these holes.
The liners are crushed, for lack of a better term, to fit into the piston blank. The smallest end is then inserted through the corresponding holes of the blank. Once in place, the ends of the liner are roughly expanded by hand. This is done more to hold the liners in place at this point and not to completely fit them to the liner. That will come later (see Liner Expansion). The entire process is repeated until all of the liners are in place.