Violin construction and mechanics
A violin consists of a body or corpus, a neck, a finger board, a bridge, a soundpost, four strings, and various fittings. The fittings are the tuning pegs, tailpiece and tailgut, endpin, possibly one or more fine tuners on the tailpiece, and in the modern style of playing, usually a chinrest, either attached with the cup directly over the tailpiece or to the left of it. There are many variations of chinrests: center-mount types such as Flesch or Guarneri, clamped to the body on both sides of the tailpiece, and side-mount types clamped to the lower bout to the left of the tailpiece.
Body
The body of the violin is made of two arched plates fastened to a "garland" of ribs with animal hide glue. The ribs are what is commonly seen as the "sides" of the box. The rib garland includes a top block, four corner blocks a bottom block, and narrow strips called linings, which help solidify the curves of the ribs and provide extra gluing surface for the plates. From the top or back, the body shows an "hourglass" shape formed by an upper bout and a lower bout. Two concave C-bouts between each side's corners form the waist of this figure, providing clearance for the bow.The best woods, especially for the plates, have been seasoned for many years in large wedges, and the seasoning process continues indefinitely after the violin has been made. Glue joints of the instrument are held with hide glue since other adhesives can be difficult or impossible to reverse when future repairs are in order. Parts attached with hide glue can be separated when needed by using heat and moisture or careful prying with a thin knife blade. A well-tended violin can outlive many generations of violinists, so it is wise to take a curatorial view when caring for a violin.
Top
Typically the top is made of quarter-sawn Norway spruce, bookmatched at a strongly glued joint down the center, with two soundholes precisely placed between the C-bouts and lower corners. The soundholes affect the flex patterns of the top and allow the box to breathe as it vibrates. A decorative inlaid set of three narrow wooden strips, usually a light-colored strip surrounded by two dark strips, called purfling, runs around the edge of the top and is said to give some resistance to cracks originating at the edge. It is also claimed to allow the top to flex more independently of the rib structure. Some violins have two lines of purfling or knot-work type ornaments inlaid in the back. Painted-on faux purfling on the top is usually a sign of an inferior violin. A slab-sawn bass bar fitted inside the top, running lengthwise under the bass foot of the bridge, gives added mass and rigidity to the top plate. Some cheaper mass-produced violins have an integral bass bar carved from the same piece as the top. Ideally the top is glued to the ribs and linings with slightly diluted hide glue to allow future removal with minimal damage.Back and ribs
The back and ribs are typically made of maple, especially Norway Maple or Sycamore Maple, most often with a matching striped figure, called "flame." Backs may be one-piece slab-cut or quarter-sawn or bookmatched two-piece quarter-sawn. Backs are also purfled, but in their case the purfling is less structurally important than for the top. Some fine old violins have scribed or painted rather than inlaid purfling on the back. The small semicircular extension of the back known as the "button" provides extra gluing surface for the crucial neck joint and is neglected when measuring the length of the back. Occasionally a half-circle of ebony surrounds the button, either to restore material lost in resetting the neck of an old instrument, or to imitate that effect.The ribs, having been bent to shape by heat, have their curved shape somewhat reinforced by lining strips of other wood at the top and bottom edges. The linings also provide additional gluing surface for the seams between the plates and the rib edges.
Neck
The neck is usually maple with a flamed figure compatible with that of the ribs and back. It carries the fingerboard, typically made of ebony, but often some other wood stained or painted black. Ebony is considered the preferred material because of its hardness, appearance, and superior resistance to wear. Some very old violins were made with maple fingerboards carrying a veneer of ebony. At the peg end of the fingerboard sits a small ebony or ivory nut, infrequently called the upper saddle, with grooves to position the strings as they lead into the pegbox. The scroll at the end of the pegbox provides essential mass to tune the fundamental body resonance and provides a convenient grip for spare fingers to brace against when tuning one-handed. Some "scrolls" are carved representations of animal or human heads instead of the classical spiral volute most normally seen. The maple neck alone is not strong enough to support the tension of the strings without distorting, relying for that strength on its lamination with the fingerboard. For this reason, if a fingerboard comes loose, as may happen, it is vital to loosen the strings immediately. The shape of the neck and fingerboard affect how easily the violin may be played. Fingerboards are dressed to a particular transverse curve and have a small lengthwise "scoop" or concavity, slightly more pronounced on the lower strings, especially when meant for gut or synthetic strings. The neck is not varnished, but is polished and perhaps lightly sealed to allow ease and rapidity of shifting between positions.Some old violins have a grafted scroll or seam between the pegbox and neck. Many authentic old instruments have had their necks reset to a slightly increased angle and lengthened by about a centimeter. The neck graft allows the original scroll to be kept with a Baroque violin when bringing its neck to conformance with modern standard.
Bridge
The bridge is a precisely cut piece of maple, preferably with prominent medullary rays, showing a flecked figure. The bridge forms the lower anchor point of the vibrating length of the strings and transmits the vibration of the strings to the body of the instrument. Its top curve holds the strings at the proper height from the fingerboard, permitting each string to be played separately by the bow. The mass distribution and flex of the bridge, acting as a mechanical acoustic filter, have a prominent effect on the sound.Tuning the violin can cause the bridge to lean, usually toward the fingerboard, as the tightening of the strings pulls it. If left that way, it may warp. Experienced violinists know how to straighten and center a bridge.
Sound post and bass bar
The sound post or "soul post" fits precisely between the back and top, just to the tailward side of the treble bridge foot. It helps support the top under string pressure and has a variable effect on the instrument's tone, depending on its position and the tension of its fit. Part of adjusting the tone of the instrument is moving the sound post by small amounts laterally and along the long axis of the instrument using a tool called a sound post setter. Since the sound post is not glued and is held in place by string tension and being gently wedged between the top and back, it may fall over if all the strings are slackened at once.Running under the opposite side of the bridge is the bass bar. While the shape and mass of the bass bar affect tone, it is fixed in position and not so adjustable as the sound post. It is fitted precisely to the inside of the instrument at a slight angle to the centre joint. On many German trade instruments it used to be common fashion not to fit a bass bar but to leave a section of the front uncarved and shape that to resemble one. During the baroque era, bass bars were much shorter and thinner.
Tailpiece
The tailpiece may be wood, metal, carbon fiber, or plastic, and anchors the strings to the lower bout of the violin by means of the tailgut, nowadays most often a loop of stout nylon monofilament that rides over the saddle and goes around the endpin. The endpin fits into a tapered hole in the bottom block. Most often the material of the endpin is chosen to match the other fittings, for example, ebony, rosewood or boxwood.Very often the E string will have a fine tuning lever worked by a small screw turned by the fingers. Fine tuners may also be applied to the other strings and are sometimes built into the tailpiece. Fine tuners are usually used with solid metal or composite strings that may be difficult to tune with pegs alone; they are not used with gut strings, which have greater flexibility and don't respond adequately to the very small changes in tension of fine tuners. Some violinists, particularly beginners or those who favor metal strings, use fine tuners on all four strings. Using a fine tuner on the E string or built-in fine tuners limits the extent to which their added mass affects the sound of the instrument.
Pegs
At the scroll end, the strings ride over the nut into the pegbox, where they wind around the tuning pegs. Strings usually have a colored "silk" wrapping at both ends for identification and to provide friction against the pegs, as well as protect the windings. The peg shafts are shaved to a standard taper, their pegbox holes being reamed to the same taper, allowing the friction to be increased or decreased by the violinist applying appropriate pressure along the axis of the peg while turning it. Various brands of peg compound or peg dope help keep the pegs from sticking or slipping. Peg drops are marketed for slipping pegs. Pegs may be made of ebony, rosewood, boxwood, or other woods, either for reasons of economy or to minimize wear on the peg holes by using a softer wood for the pegs.Attempts have been made to market violins with machine tuners, but they have not been generally adopted primarily because earlier designs required irreversible physical modification of the pegbox, making violinists reluctant to fit them to classical instruments, and they added weight at the scroll. Early examples included large geared pegs that required much larger holes and/or bracing bars and additional holes, and tuning machines resembling those on a double bass, with metal plates screwed to the sides of the pegbox. Recent advances in machining technology have allowed the creation of several types of internally geared pegs the same size as the usual wooden pegs, requiring no more modification than would be seen in any peg replacement.