A machine head, also called a tuner, tuning peg, or tuning machine, is part of a guitar or similar instrument, an apparatus for tensioning and thereby tuning a string, usually located at the headstock. A headstock has several machine heads, one per string.

Construction and action

Traditionally, a single machine head consists of a pin, mounted at the centre of a pinion gear, a knob or "button" and a worm gear that links them. The pin has a hole through the far end from the gear, and the string is made to go through that hole, and is wrapped around the pin. To complete the string installation, the string is tightened by turning the pin using the tuning knob. The worm gear ensures that the pin cannot turn without a movement on the knob; it also allows precise tuning.

The guitar player adjusts the tension of the various strings using the knobs so that they are correctly tuned: a higher tension yields a more treble sound, a lower tension a bassier sound. Typical tensions for steel-string acoustic guitars with "light" tension strings are 10.5 kgf (23.3 lbf, 103 N) to 13.8 kgf (30.2 lbf, 135 N).

Varieties

Normally, worm gears provide a gear ratio of 14:1, though versions with 18:1 gear ratio also exist. They provide better accuracy in fine tuning, though are somewhat slower for initial string winding.

Several kinds of machine head apparatus exist:

• on classical guitars (with nylon strings), the worm gears are generally exposed; the strings are wound on the pins inside grooves in the head;
• on steel-string guitars, including "folk" acoustic guitars and electric guitars, the worm gears are generally placed in sealed enclosures with permanent lubrication; several machine head placements are possible, depending on the shape of the headstock:
  • rectangular head, 2 rows of 3 pins (or 6 pins for 12-string guitars): found on most "folk" guitars and on Gibson Les Paul guitars;
  • a single diagonal row of 6 pins: found on Fender Telecaster and Stratocaster guitars;
  • one diagonal row of four pins and one diagonal row of two pins: found on Music Man guitars;
• on bass guitars, string tension is extremely high and particularly heavy-weight and big machine heads are used; tuning knobs are also generally a lot bigger than guitar ones; also gear ratios of 20:1 are used often.

  Since 1950s, guitar performance techniques evolved, and aggressive usage of tremolo arm became widespread. However, the original machine heads couldn't withstand the rigors of constant string tension changing, and strings got out of tune after using tremolo several times. Several manufacturers, namely Grover, introduced a new design, commonly named locking machine heads nowadays: a machine head with additional mechanism to lock it in place and stabilize tuning while playing and using tremolo. However, such machine heads reached limited success, mostly because of their price: as of 2006, locking ones are about 50% more expensive than original. Many break strings when tension is increased while the mechanism is locked and later unlocked, which frequently happens in music stores.

  Note that on some guitars, such as those with Floyd Rose bridge, string tuning may be also conducted using microtuning tuners located at guitar bridge. In this case, main machine heads at headstock may be missing entirely, as well as the headstock itself.

  Notable designs

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  Several manufacturers established well-known designs of knobs and whole machine heads. These designs are subject to copy and reference:

  • Rodgers
  • Grover-style
  • Schaller-style
  • Kluson-style
  • Wilkinson-style
  • Fender-style
  • Gibson-style
  • Speedwinder

  References

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  There are several US patents on machine heads, mostly covering various aspects of locking:

  String instruments | Guitar parts and accessories