The problem of bore ovalization
by Áurea Domínguez
One of the main problems instrument makers confront while reconstructing a historical instrument is that throughout the years, the wood may have suffered various modifications in its life as an instrument since construction. There are several factors contributing to the deterioration of material with woodwind instruments, the most important being the humidity exposure during its use over several decades. One normal deterioration found in instruments like the bassoon is that the inner bore acquires a certain ovalization. Together with conditions of its use, there are significant factors such as the hardness of the material and the way the wood was initially cut, which are general points to consider while building instruments.
After the precise 3D-scan
s of the instruments, we decided to address this issue by creating two models of each instrument: one with little or almost no modification of the current inner bore, including any possible ovalization of the original instrument, and the other in which flaws were corrected, creating a round-bore version of instrument as it was first conceived.
As the 3D-scans demonstrated, the four instruments in our study show different degrees of ovalization. The least oval instrument is FT6 Anonymous (7) 8-key tenoroon, while FT50 Grenser (3) 6-key fagottino shows the greatest degree of ovalization. It is worth noting that FT6 is made of a hard tropical dark wood and the FT30 Scherer (4) 5-key fagottino, of boxwood. The other instruments used in this study are made of softer maple.
In order to have an idea of the degree of ovalization, we have created the following graphics that illustrate the issue. The Y coordinate shows the diameter expressed in mm of the inner bore, while the X represents the exact point where the measurement was taken. Putting together the greatest and smallest diameters measured throughout the bore makes it possible to represent the degree of ovalization. If the lines converge, the ovalization is minimal while in the cases where there is a divergence between the diameters, the ovalization of the bore is larger.
The following images show the different degrees of ovalization of the wing joint in our four studied instruments. The graphs follow the method described.
As Figure 1 shows, the FT6 wing joint shows almost no ovalization. Larger and small diameters are almost identical.
Figure 2 represents the wing joint of FT42 Savary jeune (11) 11-key tenoroon. It shows a slight degree of ovalization in the bore in the lower part of the wing joint, with the largest variation somewhere in between tone holes D and E. The bore in the bocal well shows almost no degree of ovalization.
Represented in Fig. 3 and Fig. 4, the two fagottini, FT30 Scherer (4) 5-key fagottino and FT50 Grenser (3) 6-key fagottino show a larger degree of ovalization than the previous cases. These are more homogeneous, as each entire wing joint shows similar differences between both diameters throughout the whole bore.
The bores of the butt joints also present different degrees of ovalization depending on each case. It is worth noticing however, that both tenoroons, FT6 and FT42 present little or almost no ovalization. On the other hand, the fagottini FT30 and FT50 bores have some ovalization, particularly the smallest bore of the butt joint of FT50 Grenser.