So I have a cheap acoustic guitar that I bought a while back. The action is very low and the frets buzz pretty bad when played. I would like to fix it by myself, not taking it to a guitar shop because I've already spent too much money repairing it and I bought a replacement. So what could I do to fix the neck?
sigs suck
Such a guitar offers a great oppertunity to hone your DIY skils. It's cheap, crappy and yours, while a good replacement is already at hand. Perfect.
I'd check the neck curvature first, especially if your guitar didn't have a low action initially. Hold the fat E down on the first and the 20th or so fret and look underneath. Nowhere should the string touch other frets. The string should hover about a millimeter over the top of the fret halfway between where you hold it down. If the neck is bent backwards (all the frets are touched, no gap is visible), release the truss rod tension (if of course we're talking steel string guitars here, not nylon string for these rarely have a truss rod) Normally this shouldn't be necessary, but if you doubt the quality of your truss rod, release the strings first before you twist the rod. Go about in quarter turns between measurements (measure when tuned back to pitch) and always use a quality allen key; crappy tools wreck things rather than fix them.
Then see if the lower most frets (i.e lower in musical tems, not geometrically) are not worn beyond their limit. Flattened frets can cause fretbuzz higher up the neck and should be replaced (tricky job. Turn to this forum again if you find this has to be done)
Finally look for frets that are not rested properly in their slots, so they protrude higher than the adjecent frets. Such frets should be pushed in their slots. (you may gently tap them in place with a hammer, but never let metal touch metal and always support the neck underneath the place where you apply force. Using a piece of hard wood dampen the blow is always a good trick when hammering on delicate parts.
Only if all the above has been checked and corrected you can turn your attention to the bridge piece. The only adaquate way to correct low action is to replace the bridge piece, but a junk yard (or a third world) mechanic may try to put a few strips op carton underneath, or better a thin strip of wood of.
Finally, and most important; proceed carefully and enjoy it. If you stop enjoying, turn to your good guitar for a while till you get back in a good mood.