Introduction: Acoustic Guitar Setup
Thanks to cheap labor and mass manufacturing in China, there is a surprisingly wide variety of acoustic guitars available for around $100. So what separates these cheap guitars from those costing five or ten times as much? Modern manufacturing can maintain a relatively high build quality, so the extra money mainly goes towards using rare woods and the additional hand labor for precise set-up. It is my opinion that inexpensive guitars sound fine but can be a little awkward to play . With a little time and care though, it is possible to setup one of these inexpensive guitars with the playability of one costing ten times as much. Here are the adjustments that usually need to be made.
Step 1: Adjust the Truss Rod
The truss rod is used to provide counter tension against the strings to keep the neck in the proper position. It is not used for adjusting the action, this is done in later steps at the nut and bridge. The head of the truss rod is accessed at the top of the neck or from within the sound hole depending on the guitar.
To check the tension on the neck, first make sure the guitar is properly tuned. Then place a capo on the first fret and press down the first string at the 14th fret. Now check the clearance at the 6th fret. You should be able to just fit a piece of heavy card stock (index or business card) under the string at the 6th fret. Tighten the truss rod to decrease the clearance. Loosen the truss rod to increase the clearance
The diagram was found at: http://www.taylorguitars.com/global/pdfs/truss_rod_adjustment.pdf
Step 2: Check the Neck Angle
Most setup guides that I have referenced seem to skip over this crucial step. Ideally the neck should be mounted onto the guitar body with a very slight angle; with no tension in the strings and the guitar laying on its back, the neck should be angled slightly downward so that the top of the fretboard is on the same plane as the guitar body. With a straight edge against the body of the guitar, the neck should decline until the top of the fretboard is inline with the straight edge right before the nut.
Step 3: Check the Neck Angle
Here is the neck angle on a $80 guitar I picked up recently. It does have a slight angle, but in the wrong direction
Step 4: Correcting the Neck Angle
With the proper neck angle, the plane of the fretboard should intersect the top of the bridge. This can also be confirmed with a straightedge. The image shows an example of how a poor neck angle affects the alignment with the bridge.
***I should confess that I didn't decide to put together the instructable until the project was underway. The image shows the bridge after I had already started sanding it (which is no secret from the way it looks). Originally it was even higher.
Step 5: Correcting the Neck Angle
Since we can’t easily change the plane of the neck, the only option is to adjust the bridge. I sanded off about 1/8 of an inch to get the bridge inline with the fretboard.
Since the thickness of the bridge can affect the sound of the guitar, I decided to cut a few string grooves behind the saddle to minimize the amount I lowered the entire surface.
***I've had a few questions about why it is necessary to lower the bridge in addition to lowering the saddle. Here is an answer I posted:
The other reason (maybe more obvious) is that if the neck is misaligned you could shave the saddle all the way down to the groove it sits in and still not have the action low enough. In the case with the guitar pictured, I ended up sanding down the saddle to a point below the original plane of the bridge. If I didn't sand down the bridge the saddle wouldn't have even risen out of the groove!
Step 6: Adjusting the Nut
After fixing any problems with the truss rod or neck angle you can start adjusting the action at the nut. This is done by pressing each string down after the second fret and checking the clearance above the first. The clearance should be adjusted to the thickness of an index card:
Step 7: Adjusting the Nut
Reduce the clearance by carefully filing down the string grooves with a thin needle file:
Step 8: Adjusting the Nut
Once the nut is adjusted I recommend lubricating the grooves with a teflon based machine oil. This will prevent the strings from burrowing down further into the nut as they are tuned. It also prevents burrs from forming and catching against the string, causing it to break when tuning the guitar.
Step 9: Adjusting the Saddle
The height of the saddle is the main component in determining the action. Only begin adusting the action at the saddle after you have completed all of the other steps. It is adjusted by removing material with sandpaper and a sanding block.
The top should be slightly contoured to allow the thinnest strings to sit a little lower. The overall action varies based on preference but a clearance of 3/16” above the 12th fret is a typical rule of thumb. I recommend buying a few acoustic guitar saddles (I found them online for $1.50 each) to allow the freedom to experiment and find the best setup.
Step 10: Finishing Up
If you change the gauge of your strings you should double check the truss rod and bridge. Thicker strings will produce more tension and will need a bit more force to counter it. Also, they require greater force against the fretboard so you may want to lower the action at the saddle to compensate. If you plan to try a new string gauge then you should plan on ordering a new saddle also.
Going through these steps may take some time but it will be worth the effort. Now that you know what to look for, the next time you walk through a guitar shop check these parameters on a few guitars and you will be surprised at how variable the factory setup can be. It will put a smile on your face when you compare the playability of your properly adjusted $80 guitar to some costing several hundreds of dollars but still in need of a little work.
The image shows the final result with the saddle mounted and a fresh coat of varnish over the bridge.