Setting Up a 12 String Acoustic For Better Action.

Filing the nut for the thicker gauges.

Filing the bridge down for the thicker strings.

I recently bought this late 70's Yamaha 12 string acoustic for about $70, which was a steal.  I think the shop I bought it at didn't realize the quality of the guitar because it did look as if it had been neglected for years and the action and playability was like a boxing match with Muhammid Ali for 9 rounds.  A constant struggle.  The Strings were too high to start with.  This was an easy fix.  I simply sanded down the bottom of the bridge and adjusted the trust rod, to my liking.  The other real problem was that the nut and the bridge were level and straight.  This causes a real problem when you want to fret a pair string pair.  The thicker string ends up being higher than the thinner gauged string.  Makes for clumsy fret work when playing.  So, to put the string at the same level point from the top, I stared with the nut.  I simply filed down and widened each thicker string gauges slot until the strings were level.  Next up, the bridge.  I slotted down each point were the thicker string ran across the bridge.  The playability really improved.  However, I ran into one last problem, the thicker strings were barely touching the bridge at this point.  The contact point was a little too low.  To fix this and to keep the action low, I filed out part of the bridge base were the string runs into the bridge pin.  Making the strings angle over the bridge contact much sharper, keeping the string snuggle over the bridge.  These adjustments took a bit of adjusting and time playing between each change to get everything just right.  It paid off.  I'm surprised these adjustments aren't standard on all 12 strings, considering the uniqueness the instrument poises. 

Routing the thicker strings lower in the bridge.