Adjust Action (Set-up)The term "action" basically refers to the way an instrument is adjusted and how well it plays. Action adjustments are made to improve the feel of the instrument, decrease pressure on your fingertips which can be severe when the action is too high, avoid buzzing and generally just get the best sound out of an instrument. Most instruments are set-up at the factory with higher action then necessary. High action on a brand new instrument may be the result of settling (all that tension on a newly built instrument is bound to change it's shape a bit), a change in it's environment (factories assemble instruments under closely controlled temperatures and humidity) or simply because many factories agree that it's easier to drop the action than it is to raise it. Raising action can require replacement of the nut and saddle, a more costly undertaking than merely cutting them both lower.
Things that may directly affect your instruments action are:
Humidity (or lack thereof) Moisture causes the woods of an instrument to swell, loss of moisture will cause them to shrink.Most will find that during the summer or times of high humidity the top may swell and lift the strings higher off of the fingerboard making it more difficult to play. On the other hand, instruments that have been left without proper humidity will often become dry, which can cause the top to drop and create buzzing problems. You may also encounter sharp fret ends that are now exposed due to the shrinking of the fingerboard. During times of low humidity it is essential that you keep your instrument properly humidified. Read more about humidity.
Wear and TearThe grooves of the nut and/or bridge saddle will wear as the strings pass over them. As the strings pull to and fro across the nut and saddle they are slowly but surely deepening the groove.Excessive wear in the nut slots may cause the strings to buzz when played open since they are now too close to the frets. Grooves in the saddle can affect intonation and cause strings to break.
TensionIt is particularly common for the action on flat top instruments to raise over time due to the tension placed on the top. The strings continual pull on the bridge and top can create a slight arching which raises the action over time. While a slight arch is quite normal, greater changes in the tops shape may be and indication of structural problems such as loose braces or a warped or cracked bridge plate.
String gauge If you change the gauge of strings you are using, be it heavier or lighter, there will be a change in tension on the top and neck of the instrument. When setting up an instrument you must choose what gauge of string you will be using so that the action can be adjusted accordingly. Changing the string gauge will affect your set up. Read more.
Playing StyleThere is no such thing as a "cookie cutter set-up" in my book. While you will find many references and measurements as to string height above the frets these are basically a means to communicate with others and set certain standards whereby to make comparisons. While measurements help to put you in the ballpark of a good set up there are differences which will factor into each instruments ideal set up. The action on an instrument played by an aggressive strummer or flatpicker will vary greatly from that for a jazz player or fingerpicker.
Structural Problems Loose braces, loose bridges, loose necks, cracks and other structural problems may first become apparent when a player notices a significant change in an instruments action.
Depending the abilities of the instrument and the needs of the player adjustments can be made to improve the instruments action and increase the comfort of playing. I like to have my customers play a little for me, even if they're just beginning. The opportunity to communicate and watch someone's playing style goes along way in helping me to get it just right.
Setting Up An Instrument
Typical adjustments that improve action are:
Correct Action at the Nut The nuts slots require:
Correct overall string spacing to prevent the outer strings from rolling off of the fingerboard edges
Correct string to string spacing
Correct angle on the bottom of the slot to provide sustain and clarity
Correct width to keep the strings from binding in the slots
Correct slot depth to provide the appropriate gap between string and fret
Correct Action at the Saddle Saddle height is a major factor in the overall string height (action) of the instrument. Raising or lowering the saddle will have a direct affect on the instruments action and the height of the strings above the fingerboard. Saddle radius or contour also affects the instruments action.
Correct Neck Relief (Bow)Appropriate relief (bow) in the neck gives the strings amble room to vibrate without hitting the frets and affects the action more so towards the center of the neck.
Level & Well Dressed Frets Frets should be level, have a nicely formed crown and ideally, be free from deep grooves or heavy scratches.
Correct Intonation If you are a beginner or 1st position player, correct intonation may be of little consequence to you now, but as you begin to play up the neck, poor intonation becomes terribly apparent. The further up the neck you play the more out of tune the instrument is. Adjustments to intonation are always done after all set up work and tweaking is complete.
How high/low do I want the strings? Well this is a difficult area to be all encompassing and absolute about since there are no cookie cutter set-up's, not all instruments play the same with the identical set-up and a player's pick attack or style will dictate certain aspects, so.......with all that in mind, please bear in mind that this is a general scale for accessing your instruments action.
You'll need a ruler that reads 32nd's to keep up.
Place a ruler on top of the 12th fret (see below) and read the point at which the bottom of the bass E string lies. Most factories choose 3/32" to be a good starting point for most flat top acoustic guitars. Though some aggressive strummers or bluegrass players will enjoy an action closer to 1/8", you will rarely find reason for it to be that high. And at 5/32" you'll be thinking of taking up the drums! Ugh, moocho painful! Gentle pickers, jazz musicians and fingerpickers can often squeak by with less but so much depends on the instruments ability and your style. You will find that ideally this measurement will decrease in very small increments as you move towards the treble strings, ending with just a bit over 2/32 at the treble E string. The tiny treble strings do not require as much height from the fingerboard as their vibration pattern is smaller.
5/32" at 12th fret Yowee! Where are those drum sticks? While I consider this action far too high to serve anyone but a slide guitarist, I've actually seen them higher than this. High action makes for painful playing and awful intonation.
