course of playing, hairs are often lost from the bow, making it necessary to have it rehaired periodically, which is done by professionals at roughly the cost of a new set of strings. Other maintenance may include replacing the wire lapping and leather grip or lubricating the screw. Large cracks and breakages in the bow are usually fatal; they cannot be repaired like the body of the violin can. A bow which has warped and is no longer straight can sometimes be bent back to true or re-cambered, but this must be done with heat by a craftsman and is not always successful or worthwhile. Loosening the hair when the bow is not being used helps keep the bow from becoming "sprung" or losing its camber and the hair from becoming stretched. In the 2020s, there are bows available made from fiberglass or carbon composite which are less fragile. Some of the fiberglass bows are much cheaper than wooden bows. The best carbon composite bows are used by some professional musicians. Sound post adjustment The position of the sound post inside the violin is critical, and moving it by very small amounts can make a substantial difference in the sound quality of an instrument. The thickness of the post is important as well. Sound post adjustment is as much art as science, depending on the ears, experience, structural sense, and sensitive touch of the luthier. Moving the sound post has very complex consequences on the sound; in the end, it is the ear of the person doing the adjusting that determines the desired location of the post. Here are some rough guides to how sound post placement influences the sound quality of the instrument: If the sound is too thin and shrill, the post may be too near the f hole or too tight, or the post may be too thin. If the sound is weak and there is a loss of power (especially in the lower register), the post may be too near the center of the instrument. If there is a loss of overall power and tone, the post may be too far behind the bridge, or the post may be too thick. Schools The traditional path into violin making is through apprenticing under an experienced luthier. However, there are also schools, and classes within universities, which may focus on different areas of violin making or repair, and