Backing is the procedure in which the notes are given their arched, convex shape. This is not done by raising the note areas, but by lowering the surface between them. When the backing is finished the note areas should curve outwards, while the rest of the drum surface should be concave. For an explanation of the usage of the terms convex and concave, see appendix E.
The main reason for doing the backing is presumably to form note dents with a proper arch and internal tensions that later are to be conserved by the grooving. Another reason for doing some of the shaping before the grooving is that the grooves would presumably burst if all this stretching of the metal was done after the grooving.
Fig. 4.1 Backing.
The backing is done with the backing hammer, see fig. 4.1 and appendix B. The size of the head of the hammer makes it impossible to work only between the notes, you have to hit a bit up on the notes, too. This is actually the right thing to do, as the result is meant to be dents with a smooth arch beginning at the groove mark, see fig. 4.2.
During the backing you may notice that the surface tends to move dynamically when it is hit in one place it comes up elsewhere. The goal in backing is to get the metal down everywhere except in the note areas. A skilled panmaker knows exactly how hard to hit to put the surface at the right level without making it come up elsewhere. He also smooths the surface and adjusts the arch of the notes with gentle strokes while he is doing the backing.
The result of the backing should be smooth note dents that are "relaxed", which means that they are able to vibrate more freely than the rest of the surface.
Fig. 4.2 Cross-section of backing result. Heights of dents are exaggerated.
Backing outer notes
The outer notes are first backed by hitting on the radial lines going from the rim towards the centre. Begin at the rim and work down at each side of the note, one at a time. You may have to hit quite hard to get the note surface to raise in the right way, especially on tenors. The backing should extend about 2-3 cm in on the note surface, inside the groove mark. After the two radial lines of a note have been backed, its inner border is backed, see fig. 4.3. Here the backing is often done fully on the inside of the marking, i.e., 3-5 cm up on the note, see fig. 4.4.
Fig. 4.3 Sequence for the backing of outer notes.
Lower the borders between the outer notes in this way all around the drum. Watch the height of the dents closely to get them level with each other. If necessary, adjust the arch of the dents by hitting upon them with a couple of soft strokes. The height of the outer notes for a double tenor or a tenor pan should be about 1-2 mm at this stage. Most of the surface inside the marks for grooving should be convex after the backing, but some parts near the rim may still be concave.
Fig. 4.4 Backing the inner end of an outer note.
Backing of inner notes
After the backing of the outer notes, the inner notes are to be treated in the same way. The surface between the notes and the border marks is hit to make the inner note dents raise.
Fig. 4.5 Going round the drum while backing between inner and outer notes.
First, work round the pan in the small area between the inner and the outer notes, see fig. 4.5. In practice, this can be seen as an extension of the backing of the outer notes, you just work a bit further in. This will continue to raise the outer notes as well as parts of the inner ones. After the first round, work around the pan a second time and back a bit further down between the inner notes, see fig. 4.6.
Fig. 4.6 Backing between inner and outer notes.
Second, hit the surface between the inner notes, working from the centre towards the outer notes, see fig. 4.7. Keep your eye on the rest of the surface all the time, because when you hit in one place it will raise at other places. Try to keep those places down at the same time.
The backing has to be done in a circular manner, because while you are working at one side of the pan, the other side will be affected by stretching forces so that the surface there is raised.
Fig. 4.7 Backing between inner notes.
When the backing of the inner notes is done, you may have to go back and adjust the inner borders of the outer notes, as they may have been affected by the backing of the inner notes.
Last, the different notes are adjusted until they are level with each other. If necessary, the overall shape is adjusted again. At this stage you should begin to hear sounds from the notes. If the backing is correctly done, no sound should be heard from the surface between the notes.