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Setting Up a Guitar
One of the most important factors in the playability of a guitar, the way it feels when you fret with your left hand, how much force it takes, how clean your hammer-ons and pull-offs feel, is the set up of the guitar. In the simplest terms, the set up is the distance that the strings are above the frets.
The higher the strings are above the frets, the higher the action is, the "higher" or "harder" the set up is. The lower the strings are above the frets, the lower the set up is and the softer it is.
The set up is key in these factors:
a. The feel of the guitar: How hard is it to fret b. The compensation (a lower action requires less compensation c. The "speed" of the fretboard, how quickly you can change pitches d. The cleanness of your hammer-ons and pull-offs
Most people find these factors very important in the quality of their playing and how it feels to play.
Most people, most of the time, want the action "as low as possible without buzzing". Some flat-pickers like to dig in pretty hard and may prefer a higher action.
Key to a low, clean action is good fretwork. I level the frets of every guitar prior to doing the set up. This entails leveling the crowns with a dead-flat file, then re-crowning the frets with another special file and then smoothing them with a special file to round the fret ends, and successive grades of sandpaper through 0000 steel wool to make the frets very smooth and make them shine.
After preparing the guitar for set up by leveling the frets, I then make the nut and saddle (typically from bone). When they are fitted to their respective slots, I shape their tops to the right radius to match the fretboard radius, and start the nut slots with a micro saw and then a very fine file (at the correct spacing of course; the string spacing at the saddle is set by the bridge hole locations).
Setting up the Nut
The first step in setting up is filing the nut slots to the correct height. I bring the strings down very close to the frets. If you fret the string between the second and third frets (tight to the second fret) and then hammer down with a finger close to the first fret (not right over the fret). You should hear a distinct "ping". If you look at the string from the side, you should see very little motion, more or less no motion at all as it goes to the first fret (except for the lowest string -- that one I often leave just a bit higher, so you can see the motion a little). But you must have that "ping". The ping means you have bare clearance at the first fret, which is all you need. (I learned this method from Cat Fox in Seattle.)
Setting up the Saddle
After setting the string height at the nut, I check to make sure it's tuned to pitch and then begin work on the bridge saddle. I measure the string height above the 12th fret (the 12th fret is approximately halfway between the nut and the saddle -- approximately because it's a bit further from the 12th fret to the saddle than from the 12th fret to the nut. This is "compensation" which I discuss below.) I first bring the saddle down (shorten it) to bring the string height reasonably close to the final height; but not all the way there.
I then re-tune (every time you make an adjustment at the nut, the tuning the of string changes and must be retuned; and to adjust at the saddle, you have to detune the string to remove the saddle). I then check the bow of the neck (you can see how this is done in the video, linked below). Generally, for acoustic guitars, it's best to have a slight forward bow to the neck (bare clearance on the high e string and a slight clearance (a few mils) at the low E string). I then adjust the truss rod if needed to get the correct neck bow.
Once the neck bow is correct, I then take a final measurement of the string height at the 12th fret and adjust the saddle to get the desired string height. After re-tuning, I make one final check to ensure all is as intended. Then it's time to give it a test-drive!
I normally set up the guitar a tiny bit higher than desired at the first set up. This is because the nut, saddle, and the rest of the guitar sometimes continue to "settle in" during the first few weeks after it's strung up. (Generally this is no more than 1/64th inch at the 12th fret, so you are unlikely to notice anything.)
The table below shows my typical set-up string heights at the 12th fret. These are determined by a search of the available sources for this information and also experience playing guitars of various set ups. If you want a specific set up height, I can usually do that for you. (If you want it exceptionally low, that can have other consequences, which we can discuss.)
Here's a video where I explain some about set up
Dan Luedtke, a local Minneapolis guitar teacher interviewed me in 2012 about my guitars and also some information on how to set up a guitar. (Click on the photo for a link to the video.) The video is: 9:23 (9 minutes, 23 seconds). The set up parts starts at 6:02.
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A Few Words About Compensation
Compensation is the extra bit of distance that it provided between the 12th fret and the bridge saddle (generally, the 12th fret is used as the reference point for both the set-up and for compensation, although the principle applies for the whole fretboard1.) It is a bit further (something between 0.050 and 0.15 inches at the high e string, depending -- everything depends with compensation!) from the saddle to the 12th fret than it is from the 12th fret to the nut. (The 12th fret is nominally the middle point of the free string from the nut to the saddle.)
One of the prominent features on a steel string guitar is the slanted bridge saddle. It is slanted because, on steel string guitars, there is a big difference between required compensation for the high e string and the low E string (and all the other strings in between). You may also have noticed that for most bridge saddles, the B string location has the break point on the saddle set further "back" (away from the sound hole) compared to the rest of the strings, which generally follow the slant of the saddle. Each break point is set to make the compensation "good" for each string -- each string behaves differently: Mainly each one has a different amount of tension in it and each one has a different stiffness. Both of these factors affect the compensation required.
Bridge Saddle for a Right-Handed Guitar
Bridge Saddle for a Left-Handed Guitar
Why is compensation needed?
Compensation is needed because as you fret a note, you are stretching the string. This is just like a string bend; but smaller in scale. In order to make the string sound in the correct pitch, you must add a small amount of extra string length to the free portion of the string (between the fret and the saddle). This bit of extra length is the compensation. As noted above, and shown in the photos above, the correct compensation is different for each string (on steel-stringed and electric guitars).
What affects compensation?
The most important factors affecting required compensation are: Scale length Action height String type String gauge
Most brands and models of steel strings behave quite similarly to each other; and therefore one is safe using a well-tested compensation scheme, which will produce correct (enough) tones over the entire fretboard for a wide range of strings.
Classical guitar strings generally require less compensation (they are less stiff) compared to steel strings. And the various strings within a set are usually so similar in their stiffness and tension that one compensation value suffices for all (which is why classical guitars generally do not have a slanted saddle.)
What is the correct compensation?
The "correct" compensation provides "close enough" pitches over the entire fretboard. By close enough, I mean pitches true enough for almost all listeners to find them correct and consonant. Most people will not notice a difference of 5 cents on a pitch (5% of a half-tone). (Although players with absolute pitch ("perfect pitch") may wish to have additional or special compensation.)
For all my usual designs, I know how much compensation is needed. Many of my customers have told me that my guitars are the best compensated of all those that they have owned.
Generally, when I fret a note at the 12th fret on my guitars, it comes up as right on when measured using conventional tuners, such as a SnarkTM tuner. (I like SnarkTM tuners.) They are always within 5 cents, and usually within 1 to 3 cents. Almost all players will find that this sounds very good.
For a more experimental design (unique scale length for instance), I have built a universal compensation testing machine. With this machine, I can find the correct (exact at the 12th fret) for any combination of scale length, action height, string type and gauge. So, if you want something really unique, I will make it sound great!
My Universal Compensation Testing Machine (click on the image)
Does "Perfect" Compensation Exist?
It does not, except in theory. In order to make each string perfectly compensated for each pitch (open and at each fret), you would have to make each fret segment for each string independently adjustable. Instruments like this have been conceived and built; but they are not very practical. This is because of the myriad factors that affect compensation: String type, string gauge, action height, scale length, etc. The practical result of that is: Every time the temperature or humidity changes, every time you change strings, every time you adjust the action, you would have to go through the entire set of fret segments (and the saddle) and adjust them. For a 20-fret instrument with 6 strings, that is 21 X 6 = 126 individual adjustments. Not too many people would tolerate that level of hassle to achieve "perfect" compensation -- which most people can't hear anyway.
Click here for a video of this type of guitar (every fret adjustable for each string).
Further reading: http://en.wikipedia.org/wiki/Guitar#Bridge http://www.lmii.com/scale-length-intonation http://www.lutherie.net/saddle_angle.html
See how I build guitars: Steel String Guitar Construction
These may also be of interest:
Violin construction
1 The compensation works up and down the fretboard because closer to the nut, the compensation is a smaller percentage of the total free string length; and, at the same time, the string height to the fretted note is also less (than further up the neck). This means that the string is stretched less (your are pressing it down a smaller amount) and the compensation matches well. |
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