The grooving is the process in which the note-areas are acoustically separated from each other and the rest of the surface. This is done by hitting the surface with a steel punch along the note borders, making a continuous line of punch-marks in the surface.
The purpose of the grooving is to confine the vibrations that produce the sound of each note to their own sector of the drum surface. The mechanical function of the groove is presumably to loosen up the metal and make a loose "joint". This separates the physical conditions in the note area from the surrounding surface so that the note will be able to vibrate freely. When the crafting is done the note will be a strained buckle of softer metal, while the surrounding metal will be tempered and stiff. A practical function of the groove is also to define the working area for the later tuning.
There is a special model of pans where the groove is complemented with a line of bore-holes. This makes the "groove joint" more flexible and acoustically it seems to work even better than an ordinary groove. See the section about developments for more on this "bore pan".
The tools used for grooving are a shortened nail-punch and a grooving hammer, see appendix B. The head of the punch should have a diameter of 4-7 mm. Some tuners use punches of different size for different notes in the same pan. The edge of the head have to be fairly sharp to make distinct marks in the metal. It is important that the punch has a comfortable length (10 cm is proposed) to enable good control. A longer punch would be hard to control.
Fig. 5.1 Grooving.
The grooving hammer should be a hammer that you are well acquainted with - you must know exactly how hard you are hitting. It is also important that the head is tightly fastened to the handle to get high precision in the hammering. The weight of the hammer should be approximately 0.5 kg.
It is difficult to know how hard to hit while grooving. The indication of a proper grooving is that it leaves a score in the metal that is clearly visible during the rest of the crafting and on the finished pan, without breaking the metal. It should be visible on both the playing side and the backside of the pan, but not more than that. This is because the groove mark is going to define the working area for the latter tuning.
It is better to groove a bit too light than too hard, because even if you don't go through the surface right away, the groove might burst at a later stage when the metal is stretched by the levelling. A groove that is too hard will also make the surface unnecessarily rough, resulting in a need for extra levelling work. Exactly what happens if the groove is too soft is still unclear to me, possibly the pan will be hard to tune because of interference between notes.
If you want to practice grooving before starting off, it might be useful to try on the unused top of the drum. But bear in mind that the un-stretched metal in the top is about 30% thicker and harder than the metal in the middle of the sunk bottom of the pan. This means that it can withstand harder grooving than the playing surface.
Fig. 5.2 shows what the groove should look like, when properly done. The width of the groove can vary from 4 to 7 mm. The spacing of the marks is ideally 1 to 2 mm, but can be more as long as the marks still are overlapping. If the punch jumps more than 4 mm between two successive strokes, go back and groove the place over again.
Fig. 5.2 Spacing and width of groove marks.
Grooving of inner notes
The grooving usually begins with the inner notes, see fig. 5.3. If the surface still seems rough, the region along the lines has to be smoothed before grooving. An uneven surface will make it hard to control the punch, resulting in a winding groove. Such a crooked groove will make it harder (or, at worst, impossible) to tune the note. So, if necessary, start the grooving of each note by using the smoothing hammer to even out the region along the lines. You can check that the surface is even by feeling it with your finger. It is also important that you see the note border lines well, so if they are diffuse after the backing, fill them in again before grooving.
Fig. 5.3 The grooving usually begins with the innermost notes.
The best place to start grooving on a note is where the line is straight this will make it easier to make both ends meet when you have grooved around the note, see fig. 5.4. Put the punch on the line, start hitting it about 3-4 times a second, and move it forward with a constant speed while hitting. The speed should be adjusted so that marks are made with 1 mm spacing. The grooving should leave sharp marks in the metal resulting in a continuous canal, about 1/2-1 mm deep, see fig. 5.5 to get an idea of the right result. The drum should be standing steady on the ground to enable good control over the punch, because it will jump back slightly each time you hit it.
Fig. 5.4 Detail of the grooving of an inner note.
Groove all the inner notes in the same way. The grooving of a note will affect the surface of adjacent notes, so remember to smooth the metal along the marking of each note just before grooving.
Fig. 5.5 Overview and cross-section of a grooved inner note.
Grooving of outer notes
The grooving of the outer notes is usually done by grooving the innermost borders of all the outer notes first. After this all the radial lines are grooved. See fig. 5.6 for an explanation of the grooving sequence.
Fig. 5.6 Grooving order for outer notes.
The grooving of the inner notes has re-shaped the surface and lifted the inner border of the outer notes a bit. So, before grooving, make a round with the backing hammer and put the surface back in its right place again, see fig. 5.7. If necessary, also smooth the metal at the marking of each note with the smoothing hammer before grooving.
Fig. 5.7 Levelling of inner border before grooving outer notes.
Begin grooving at the joint between the straight radial line and the inner curve. Work from one side to the other, see fig. 5.8. Work around all the outer notes in this way.
Fig. 5.8 Grooving the inner border of an outer note.
When the inner borders of the outer notes are grooved, the metal sinks down about 1 mm. It can be hard to make a smooth connection between the groove that is to go up towards the rim and the existing groove if the surfaces are not level with each other. So, before going further, the radial lines may be levelled with the backing hammer. Work around the pan hitting at the inner end of the radial lines to get them level with the existing inner grooves, see fig. 5.9.
Fig. 5.9 Levelling of the radial border of outer notes before grooving.
The radial lines of the outer notes are grooved from their inner end towards the rim. But they do not go all the way up to the rim. Use the ruler to make marks about 5 cm from the rim on all the radial lines before starting off.
Groove the lines from the point where the radial line meets the inner groove and upwards against the rim, but stop when you reach the mark, 5 cm from the rim. As you are getting closer to the rim, you have to hit harder because of the thicker metal. At the 5 cm mark, hit last hard stroke to mark the end. Work around the whole pan in this way, and the grooving is done.