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A classical and acoustic guitar setup guide.

I’ve tried here to compile all that I’ve been able to learn regarding classical and acoustic guitar setups into an article for my students at Hart’s Guitars Co. Ltd. You may not need to read the entire article because you only need to fix one issue. Below, I have color-coded simple questions that can help you navigate quickly to the part of the process you need to jump to. Welcome to Hart’s Guitars’ classical guitar setup guide!

Which type of strings are best for my instrument and my playing style?

If you’re going to go through the setup process, chances are you also want new strings. I wrote a little piece about string choice recently. Believe it or not, your choice of strings can make a yuge difference in the guitar’s playability. Do you have one guitar that is much more of a joy to play than the others. You might wanna think about trying a different type of strings on the instruments that aren’t fun to play (obviously, in addition to the setup itself). Strings by mail is a great website rabbit hole of all things strings. Find your string type suggestions there (and learn a lot about strings)!

For the newbie: Parts of the guitar

In case you are new to the world of DIY guitar setup, the illustration below can help you locate the words you might not understand related to the guitar. .

The basic Tools you’ll Need

If you can’t acquire these things, don’t fret. I’ll tell you how to make it through the setup using ordinary items instead. You won’t be able to attain the accuracy I describe, but you’ll be in the neighborhood.

Materials you may need


If you are experiencing or have one of these issues, go ahead and plan to replace the nut:

Plan to replace the saddle if you have one that is:

Section 1

Step 1. Check the neck’s “Relief”

This section is mostly for steel string acoustic readers because to adjust relief, the guitar’s neck must have a truss rod. However, some classicals and nylon crossovers have truss rods so stay with this step if you do. Look under the soundboard from above the sound hole and back towards the fretboard. Does your guitar have a little bolt under there that looks like it could be turned with an Alan wrench or some other similar tool?

If you answered YES, you have a truss rod. So, stay here and read on. If there is NO truss rod in your guitar, skip to the Action at the 12th fret section.

Guitars need to have a bit of a bow under the force of the pull the strings have between the headstock and the bridge. Total string tension on classical guitars is 80+ lbs. On steel string guitars it’s 180 lbs. for medium gauge. This tension is enough to give the neck a little bit of a bow. But, too much of a bow will make for bad action and you’ll be less likely to play your guitar. Notice the big difference between the tension classical and steel string acoustic strings? The much higher tension require a truss rod.

  1. Put a capo on the 1st fret
  2. Hold down the low E string at the 14th fret.
  3. Use a business card to check the string’s height (distance between the top of the fret to the bottom of the string) at the 6-7th fret. Try to slide the card under the string at that area.
  4. Does the card slide under the string with considerable space left under the string? If YES, that means the relief is too severe. Tighten the trust rod by moving it only 1/4 turn clockwise. Repeat the 1st three steps and re-check, repeat as needed until the string’s height is just enough to slide the card under.
  5. Does the card not slide under at all? but hit’s the string instead? If YES, the neck does not have enough relief. Loosen the truss rod in only in 1/4 turn increments, re-checking and repeating as necessary until the card just slides under the string in the 6-7th fret area. Keep notes as you go and notice the changes. Try to sneak up on the perfect setting with slow, patient decisions.

With the relief set, move on to the Action at the 12th fret section if you are not changing the nut on your guitar. If you need to install a new nut proceed below.

Section 2

If you don’t need to install a new nut, skip to section 3

Making and installing a new nut

Believe it or not, the nut will make or break your guitar’s playability in some ways. In this picture, while it may look neat, the nut slots on the high strings (to the left in the pic) are too deep .
This one is much better, but the slots are still a little too deep and maybe too wide in some areas..
Ideally, half of the string should be in the slot and half above the slot.

Steps for Making a new Nut.

  1. Acquire a nut blank that is at least the width of the beginning (1st fret) of your fretboard.
  2. Mark the middle of the nut. (use your milimeter ruler or digital micrometer to find the width and divide by two to place your mark spot on). It may be helpful at this point to label the nut’s front face.
  3. Center the nut by aligning it to the center of the fretboard. Again, use accurate measuring implements.
  4. Using a sharp pencil, mark on the nut where the left and right sides of the fretboard end.
  5. Sand the nut at both ends down to the lines marked in step #4. Try to sneak up on making it perfectly flush by sanding, fitting, the re-sanding until it feels smooth on both sides.
  6. With your nut sanded flush to the fretboard on both sides, use a very flat straight edge lain across the lower frets and extended out to the nut and mark a line with a sharp pencil where the straight edge butts up against the front face of the nut. Make a mark on the left and then the right and connect the two with a very precise line. If you have a radiused (curved) neck, you’ll need to mark it carefully at intervals all the way across the nut. If you have feeler agues, stack any combination of them to reproduce the exact height of the 1st fret then use the same stack against the nut to trace a line across its entirety.
  7. Using the marks you made into a line in step #6 on the nut, file and/or sand the nut down to where it meets the line (or a curve for radiused necks). This is called roughing-in the nut and it will give you a great starting point.
  8. For classical guitars, mark a line on the nut for the high E string exactly 13/64″ from the edge of that side of the nut and another at 5/32″ for the low E string. For acoustic guitars, those marks will be respectively at 1/8″ and 5/32.”
  9. Use a file to make a shallow groove dead-on center on the lines you marked for each string. It should be just deep enough for the string to sit in place. In the pic below, notice how different size files are used to make the slots. If you don’t have the ability to acquire a nut slot file set, look for other types of files (such as in manicuring fingernail products) to make slots of different thicknesses that closely match the width of your strings..
  10. Measure the distance between the centers of those two grooves and divide by five. For example, if the distance between the centers of each grove (at the low E and high E) is 45mm, then dividing by 5 will give a string spacing of 9mm. Use this number to mark with a sharp pencil the centers of strings 2-5.
  11. Before filing those same grooves for strings 2-5, make tiny adjustments to the spacings so that wider strings are not compacted. To do this, placing the strings across the nut and with tension added to make them perfectly straight may give a visual aid in making those micro adjustments. Make new marks on top of your previous ones to indicate where the changes are.
  12. With the new proportionally spaced marks across the nut, use a file to make a shallow groove in the same fashion as step #9. If you used the feeler gauges method, you can butt the stack of gauges up against the nut and then file the groove for each string down to the height of the stack, which will act as a safety barrier because your file will not be able to go any lower than that. Place the strings into the grooves and bring up to tension so that they’re in tune. Congrats, you have roughed in the shape of the nut. Now, go on to section 3 to rough in the height of the saddle.

Some illustrations to help you visualize these concepts.

For a more calculated approach to “roughing-in” the nut, study this image.

Below is a list of good and bad ways for strings to sit in the slots at the nut

A nice illustration of all the things that can go wrong and right with the nut end of the fretboard.

3. adjusting string height (Action) at the 12th fret

Your expensive guitar is sort of worthless if it’s annoying to play. There is a range of ideal height for your guitar strings depending on your playing style. The guitar’s action is a term that’s used to describe its playability. Saying a guitar has great action is a very subjective statement. Someone who plays lead acoustic in a bluegrass band needs an action that is very different from the needs of a person who plays jazz, chord melody, blues style, or other fingerpicking styles. My focus will be on setup for nylon stringed guitars, whether used for classical, jazz, singer songwriter, etc.

The guitar’s action is measured using, among other things, the strings’ height at the 12th fret. There’s also a 13th fret school of thought which involves putting a capo on the 1st fret and checking the strings’ height at the 13th fret. Whichever you choose, the string’s height is: the distance between the top of the fret and the bottom of the string. You’ll need a precision measuring tool to check the height of the strings at the 12th fret. Get yourself one of these:

If you don’t have one of these, order one. Until it arrives, use any ruler with metric system millimeters.
One day, I might do an illustrated book on the complete building process of a classical guitar .

Setting the action on your string when they are too high at the 12th fret.

  1. Using your measuring tool, check the distance between the bottom of the 6th string (Low E) and top of the 12th fret. It should be around 3.5 mm (.13″).
  2. Is it too high? Record the difference. For example, if your gap measures 4.2 mm make a note that there is a .7mm difference between the goal and what you have (4.2 – 3.5 = 0.7) Check the remaining strings. Look at the example below of the saddle’s height overage at the location of each string.To understand why you’d bring the saddle’s height down 6.4 mm instead of 3.2 mm, keep reading…..
  3. Make a list of the amount you’re over on each string. Make a rough drawing of the saddle’s shape, label the Low E side and High E treble side, and list the overages across it as you check them. (see illustration above ). In the illustration above, all of the strings are too high at the 12th fret, so they will need to come down by removing height from the saddle. In the drawing all strings are 3.2 mm too high or more, so it follows that 3.2 mm may be removed across the entire saddle. But wait….
  4. Think of your string as the hypotenuse of a triangle. In this case, the three sides of the triangle are: a) the flat surface of the soundboard, b) the saddle standing up is at a right angle (90 degrees), and c) the string sloping down back towards the flat pane. The sloping string is the hypotenuse. Because the 12th fret is located at exactly ½ of the length of the hypotenuse (see illustration below), you need to remove double the amount from the saddle’s height to achieve the change in height at the 12th fret you desire. (Quick Example: If you want to remove .8 mm at the 12th fret, you need to bring down the height by 1.6 mm at the saddle).
  5. Again, we are still at the stage of removing a uniform amount of height from the saddle all the way across because all of the strings’ height is still too high. Do this by sanding the bottom of the saddle, making sure to hold it at a 90 degree angle. Before sanding, think!! Do I need to remove height from ALL of my strings at the 12th fret? If your answer is yes, continue. If your answer is no, skip to #6. Use a flat/true to sand the bottom of the saddle. It’s a good idea to turn the saddle around every few strokes across the sandpaper to make sure you do not sand an angle into it. No matter how straight you might think you’re sanding it, even the best luthier’s inevitable have a bit of bias toward one side when sanding.
  6. Once you remove enough material that at least one string is at the optimum height, you’ll need to address the other strings’ height individually. Make a light mark on tight up against either side of the string (see illustration below). For the sake of reinstalling the saddle correctly when removing and reinstalling, label either side in some way that will help you orient it correctly when putting the saddle back in the slot. To make adjustments for individual strings’ height at the 12th fret, Use the same listing process as in step #2. With a sharp pencil, make a mark on the saddle’s front side, measuring down from its TOP at each string’s location. The mark you make is the amount you need to remove (remember the triangle/hypotenuse) to make the string reach the perfect height at the 12th fret. So, if your Low E string is still .7mm too high at the 12th fret, you need to make a mark down 1.4 mm from the top below that string’s spot. Repeat this process across the rest of the saddle. You’ll end up with a saddle that looks sort of like this:
  7. Connect the markings and this will make, usually, an arc that will end up being the shape of your saddle.
  8. Use a file, sandpaper, or belt sander if you have one to remove the material from the top of the saddle down to the pencil mark. Round over the corners lightly so they are not sharp (if left sharp they can break the string).!!
  9. Reinstall the saddle into its slot and bring strings back up to pitch.
  10. Check the height at the 12th fret for all the strings and repeat all the steps as necessary until every string is at optimum height. This will take time, don’t be in a hurry (especially if it’s your first go at this, oy vey!).

Make adjustments to the saddle until all strings’ heights measure in the range you want (see illustration chart above for my suggested string heights).

4. Setting action at the nut

Having the strings’ height set correctly around the 12th fret, it’s now time to take a close look at the string height at the nut. The nut is the slotted piece of bone or other dense material where the strings cross over from the tuners/headstock into the scale length beginning at the fretboard. There is an ideal height for this area as well. If you’re serious about getting your setup to professional standards, you need files of various gauges.

The slots at the nut for each individual string need to be filed according to the gauge of the string. For example, if the string’s gauge is .32 you need to use the file from your set that is one size above .32.”

Don’t skimp on this. These nut files will make tuning your guitar smooth as silk and will prevent other problems like rattling. There are many nut file sets out there. Find the one that fits your needs.

The ideal height for the strings at the nut is also somewhat subjective. I have been to many, many forums, websites, and videos. In simple, laymen’s and very effective terms, here is the best way to set the height of your strings at the nut:

  1. With the strings tuned to pitch, use a finger above fret #1 to push down on the Low E string until it touches the fret and then allow it to rise back up. Do this several times. Does the string move so much that you can visibly see it going up and down when you push on it? If YES, that particular string action at the nut is too high.
  2. Loosen and remove the string from the slot.
  3. Use the appropriate gauge nut file to remove a little bit of material from the slot (no more than a couple of decent scrapes with the file) and then tighten string and repeat the finger push test you did in #1. Knowing how much of a tiny bit of material to remove from each slot will take time. Start with two passes and note the difference. Then, try three passes and note the difference and then four. Always be aware at how much of a change there is in the string push test.
  4. Make tiny incremental adjustments until the finger push test reveals barely noticeable movement in the string.
  5. Move on to the next string.
  6. Repeat #1-4 for every string.

This can take a long time when you’re just beginning to do this. DON’T EXPECT TO MAKE IT PERFECT IN THE 1ST SITTING! Remember, you are making your guitar reach its maximum playability comfort zone and if it takes several days to a week of careful adjustments, so be it.

I recently finished a guitar was able to set the nut action in about 2 hrs. and felt like I had become a pro. Later, I went back and checked earlier guitars I made and was able to fine tune the string height at the nut a great deal on some I thought were near-perfect when I did them. This learning curve is long. Be patient if you are a beginner.

5. Intonation

With everything about your guitar playing nicely, checking the intonation is next. If your instrument has been fretted properly, you may notice a slight increase in sharpness of each note as you ascend the fretboard. That is because as strings are depressed on the fingerboard, the various thicknesses of the strings will affect the downward distance the string travels before hitting the fingered fret. So, each string’s resulting length is partially dependent on that distance. Saddle compensation helps normalize effective string length. It’s not a perfect solution, but intonation is improved noticeably. This thickness/downward distance interplay challenge is best solved by having a compensated saddle length where the bass side of the saddle is moved back in relation to the other (treble side). You may notice that your saddle sits at an angle and that is because the bass side scale is extended relative to the treble.

  1. If you have read all the previous sections and fixed the issues, where needed, and are ready for the last tidbit of a professional setup, continue to follow these steps:
  2. Using a tuner app or device, bring all the strings up to pitch.
  3. Play a 12th fret harmonic (lightly touching the string but not pushing it down all the way to the fingerboard) on the low E string.
  4. Play that same string’s fretted note at the 12th fret (in this case you actually push the string down to touch the 12th fret). Is the fretted 12th note is a bit sharper than the harmonic you played in step 3? If the fretted note is sharp, then the break point of the saddle needs to be moved back. (if the fretted note is extremely sharper, then you have a more serious problem of incorrect fret location, saddle location).
  5. Use a piece of scrap guitar string a few inches long (from the high E ideally if you still have some pieces from restringing your guitar). If you don’t have any guitar strings you can cut a scrap piece from, find any sort of wire, fishing line, etc that relatively matches the thickness of that high E string.
  6. Beginning with the low E, release the tension of the string down enough so that you can place the scrap piece of string along the top of the saddle under the Low E (see illustration).
  7. Play a 12th fret harmonic (in tune, of course).
  8. Then play the note at the 12th fret using your finger.
  9. Is the note a little bit sharp? If yes, pull the piece of scrap string back (opposite direction/away from the headstock) just a tiny amount so that it remains on the saddle but is farther away nonetheless. Play the note at the 12th fret again. You’ll notice that it’s closer to pitch this time.
  10. Is it still a bit sharp? If YES, repeat the process of moving the scrap piece back until the fretted note plays in tune with the open harmonic. If your string happened to be a little flat, then move it in the opposite direction (towards the headstock).
  11. When the open harmonic and the note match perfectly, use a very sharp pencil to score a line on both sides of the scrap piece. Make your pencil as sharp as possible and score the line with its point butted up as precisely as possible against the string.
  12. Repeat these steps for all strings.
  13. With all of your markings done, release the tension on your strings until you can slide the saddle out of the slot.
  14. With the saddle out of the slot, use a file to remove material from the saddle in the direction of your pencil markings on both sides. This will establish the new break-point for your strings and they will play in tune in the higher frets.
  15. Round-over this new peak so that it’s not too sharp otherwise it will not be good to your strings. This is the new break angle for that individual string. Repeat this process for all strings.
  16. Congratulations! You have adjusted the intonation of your guitar!

Please help me help you. Give me a little quick feedback?

Final Thoughts

The first time I adjusted a guitar’s action, I felt like I had added $400 to its value. The difference was remarkable. I felt like a magician. But, guess what? It ain’t rocket surgery, as my friend Nichols used to say. Simply follow the sequence of steps I describe in this article and you’ll be able to feel the same thing I did when the owner played that guitar whose action I had just adjusted, her mouth open wide and eyes even farther. “It’s like a whole new guitar;” the best words any fledgling luthier could ever hear.

Bring your guitar to me if you need it to play well again but you don’t have the time to do it yourself. This process can take some time to develop. A year or so after I began researching the process and doing that first setup, I can go back and see my initial work with a fondness of those early days and excitement around learning this stuff. I was able to tweak those 1st instruments I worked on to make them better. Don’t expect perfection the 1st go! Best of luck!

Classical and acoustic guitar setup guide at Hart’s Guitars.

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