1. Adjusting and tuning flutes
Pitch can be altered in two ways: by altering the position or the size of a hole. Making the hole larger will raise the pitch, and this can be done either by burning, carving or sandpapering the hole, but by far the easiest and quickest is to burn with a hot iron, which will also make a perfectly round hole (very difficult to achieve by carving). Drilling is also possible, but it carries the risk of cracking the bamboo. Holes can be made smaller by lining the circumference of the hole with glue, filler or resin. These adjustments are suitable only for small adjustments of pitch. For larger adjustments the hole has to be moved further up or down the flute. The simplest way to do this is to draw a rectangle around the hole, with the difference in the distances between the hole and the two ends of the rectangle being equivalent to the distance the hole is required to move up or down the flute. The rectangle is then cut out and reversed and glued back into place.
For example, supposing that one needed to move a hole three millimetres up or down the flute it would look like this:
The cross cuts should be made first, with a fine blade hacksaw, and the long cuts along the grain of the bamboo can be made by inserting a sharp knife (Stanley knife) and the bamboo should split fairly easily. The rectangle is then reversed and replaced with a wood glue. It may be necessary to mix the glue with a little bamboo sawdust to fill up any smail gaps.
An alternative method to moving a hole is to fill the existing hole with patch of bamboo and make a new hole where required, but this demands considerably more advanced carpentry skills.
These procedures are for putting individual notes in tune, but if the flute is already in tune with itself and the aim is to tune the instrument to a certain note of concert pitch, this can only be done by moving the blowing hole. This in a very limited operation, where only small adjustments can be made. If the blowing hole is moved more than a small amount, say 2 mm. the entire flute is affected, higher and lower notes lose their pitch, tonal quality and volume is affected.
2. Making flutes
It is essential is to get good bamboo, which is not easy. The bamboo used to make a bansuri should well seasoned (with no green streaks or patches showing) hard, even, regular and with the bamboo wall not too thin or too thick. There are too many variables to design a flute by calculations; it is best to use an existing flute as a model, and even this poses problems as it is not just the length that counts but also the diameter of the bamboo and the thickness of the bamboo wall. As no two pieces of bamboo are identical, when marking the places where the holes are to be made, small adjustments have to be made by intuition, guesswork and eventually by experience. The beginner will have to accept that mistakes will probably be made, holes wrongly placed, which then can only be corrected by the surgical procedures described above.
Generally, it is easier to tune and adjust existing flute than starting from scratch.
3. The stopper.
The stopper, or whatever means is used to stop the air escaping from the other side of the blowing hole, is usually a cork. However, in many flutes that are made in India, they are often made from other materials, sometimes soft spongy materials. It is better to replace them with a cork, suitably trimmed to the diameter of the flute, then sealed by holding a lighted candle over the end until the cork is completely covered with molten wax.
The placing of the cork is critical to the tuning of the flute. There in general tendency in most flutes for the top notes, from top Sa upwards to sound progressively flatter as one advances towards the top notes of the flute. This can be corrected by placing the cork close to the blowing hole; with many flutes it is necessary to push the cork right up to the edge of the blowing hole.
4 The Blowing hole
There are many variables in the blowing hole that will affect tonal quality and volume: the size, shape, whether the edge of the bamboo wall is vertical or cut away to leave a sharper edge, and if the bansuri is made of particularly thin or poor bamboo, the blowing hole can be cut out and replaced by a piece of thicker, harder bamboo. The bansuri player needs to experiment with these possibilities to discover what kind of blowing hole produces the particular tonal quality the he/she is striving for.