Acoustic Guitar Straight Pull Conversion

Straight pull means that the strings, when viewed from directly above, come over the guitar nut and drop to the tuner shafts without an divergence to the left or right.  Fender electrics often have this arrangement, but it's far less common on 3+3 style headstocks.  And I'll show you why.

For what purpose do I wish to do this?  I've seen differing opinions, some of them strong.  And the person in that link has a point.  In any case, when the guitar nut is viewed as a dimensionless line, the string is only going in one direction:  either it goes over the nut and straight "down" to the tuner, or it goes over the nut and "left/down" or "right/down" to the tuner.  That's a fact.  But to my mind, that misses a couple of points:

1. Straight pull just seems like it ought to be better, facts be damned
2. I like how it looks
3. The argument fails to take into account the actual geometry of the guitar nut, which is a vertical slot cut into the nut material.  A string that goes straight "down" lays naturally in this slot.  A string that goes left or right as well angles down into the slot from the front edge of the nut, then makes another angle from the back of the nut slot to the tuner.

Anyhow I'm doing it.  If I screw this all up I'll simply saw off the headstock at the scarf joint and glue on another piece, or something.

First job is to determine the natural lie of the strings.  I haven't been able to figure out a good way of doing this, really.  I figure close is good enough for this cheap acoustic.

No, wait.  The first job is to plug up the four holes that will be moved.  I used 3/8" oak dowel glued in with that same hardcore two part epoxy I used to do the fiberglass layers on my electric.

Then I put tape across the last inch of the end of the headstock, put the bridge pins in place, made a loop in a piece of string, hung it around each of the bridge pins in turn and ran it through the correct slot in the nut, and eyeballed a line on the tip of the headstock.  When the lines were pretty close to evenly spaced, I figured they were pretty close to correct (proportional string spacing or not).

Then I used a little piece of brass tubing from the torch tip cleaner kit that was almost the same diameter as the wrapping portion of the tuner shafts to mark the desired locations of the new holes.  This is hard because each of these 3/8" holes will interrupt valuable grain in the headstock material, inevitably weakening it.  So I staggered the hole locations.  

Drilling simple holes when you don't have a drill press can be an adventure as well.  Drill bits wander from starter holes; verticality becomes an issue.  I solved the wandering problem by making a template from a piece of steel stock:

Yes, really.  Then I measured from the holes to the desired edge of the headstock based on providing enough clearance for the tuner buttons to rotate.  I then made a silly flowing profile and attacked it with a coping saw, because a tilt-back guitar headstock is not easily amenable to cutting on a bandsaw.  Nice filled holes, huh?  This guitar is looking better and better every second.  

There are a million little holes on the back of the headstock where the old tuner mounting screws were removed, and where I misplaced the new tuner locator pin holes a million times.  Since strength is an issue here, I'm going to fill all the small holes with raw epoxy puddles.  I guess that should be strong, unless it's not.  I have the option of finishing the edge and face of the headstock with veneer to cover  up all the mess, but in order to do that I'd have to take away native grain and that concerns me.  I think this is just going to be an ugly guitar.