Editing Machine head (section)

== Varieties ==
Several kinds of machine head apparatus exist:
* on [[classical guitar]]s (with nylon strings), the worm gears are generally exposed; the strings are wound on the pins inside grooves in the head;
* on modern steel-string guitars, including "folk" [[Steel-string guitar|acoustic]] and [[electric guitar]]s, the worm gears are generally placed in individual sealed enclosures with permanent [[lubrication]], although budget models may have exposed gears fixed on plates housing a row of gears. Vintage and vintage-reproduction guitars frequently have individual open-gear tuners, enclosed tuners not having become common until after WWII. 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" and "Jazz" guitars and on [[Gibson Les Paul]] guitars;
** a single diagonal row of 6 pins: found on [[Fender Telecaster]] and [[Fender Stratocaster|Stratocaster]] guitars;
** one diagonal row of four pins and one diagonal row of two pins: found on [[Music Man (company)|Music Man]] guitars;
* on [[bass guitar]]s, where string tension is extremely high, larger, heavier-duty machine heads than those used on guitars are used. Bass tuners generally feature larger knobs than guitar tuners as well; often these are distinctively shaped, and known as "elephant ears".  Gear ratios of 20:1 are used often. Exposed gears are much more common in premium bass guitars than in six-string non-bass instruments.
[[File:Classical guitar head gears DSC06945.jpg|thumb|The machine heads on a classical guitar. Note the exposed gears and the decorations.]]
[[File:MartinEB18Headstock.jpg|thumb|A Martin EB18 bass guitar headstock, showing Martin open-type machine heads]]
[[File:Folk guitar head DSC06938 reverse.jpg|thumb|right|The reverse of the machine heads on a "folk" steel-string acoustic guitar. Note the enclosed gears.]]
<!--irrelevant?: Since the 1950s, guitar performance techniques evolved, and aggressive usage of a [[vibrato bar]] ("tremolo") became widespread. However, the original machine heads couldn't withstand the rigors of constant string tension changing, and strings could go out of tune after using a vibrato mechanism several times. -->

On some guitars, such as those with [[Floyd Rose]] bridge, string tuning may be also conducted using ''microtuning'' tuners incorporated into the guitar bridge.

Likewise, 'headless' guitars and basses, notably those designed by [[Steinberger]] and their licensed imitations, such as the [[Hohner]] Jack Bass, and unlicensed imitations such as the [[Washburn Guitars|Washburn]] Bantam, have the machine heads at the body end. [[Steinberger]]s and [[Hohner]]s require specialist double-ball end strings, whereas the Washburn Bantam can take regular strings.

Presently, most worm-gear tuners provide a [[gear ratio]] of 14:1. In older designs, 12:1 was common, and lower ratios as well. Lower ratios allow a replacement string to be brought more quickly up to pitch, though with less precision for fine-tuning. Lower ratios are also more forgiving of imperfect machining, and of factors that might compromise the gear surfaces (corrosion, grit, poor lubrication).

As increased precision of milling became more cost-effective, higher ratios appeared on the market, with 14:1 being the modern standard, trading accuracy against slower initial string winding. More recently, versions with an 18:1 gear ratio are available (particularly from Grover), and the Gotoh 510 offers 21:1.

===Locking tuners===
The term "locking tuners" has two meanings. Presently, it refers to some sort of mechanism in the string peg (usually a cam or screw) that locks the string in place, preventing slippage. With the popular increase of extreme [[Vibrato systems for guitar|vibrato-arm]] usage in the 1980s, several manufacturers introduced a modified design, commonly called ''locking machine heads'', where the individual tuner has an additional mechanism to lock the string in place and stabilize tuning, primarily intended for musicians who make regular use of the vibrato. Some designs increase string breakage at the point they grip the string.

The term "locking" is much older, possibly originating with Grover, and refers to an "anti-[[Backlash (engineering)|backlash]]" design of the gears, which greatly reduced the slippage of the basic [[Gear#Worm|worm-and-gear system]]. The gear's teeth are shaped to lock into those of the worm, with the string tension insufficient to overcome the friction between the gears. Such a design is called '''self-locking'''. Grover Rotomatics and similar designs from other manufacturers are rightly called "locking tuners".