There is a tool called the SaddleMatic that is designed to show you precisely where to locate the saddle of an acoustic guitar for proper intonation. This is a fine tool and it is available at Stewart MacDonald for about $40. I have a problem with it though. Namely, spending the $40!! So, as usual, I set out to make my own, with one major improvement over the original.
First, let me explain the use of this tool. It has a sliding block which has a groove cut across it's bottom.
This groove is placed directly on the 12th Fret. The other two grooves are there because presumably you can check this distance with the strings on the guitar. The jig is then adjusted so that the larger, fixed block is resting against the front edge of the nut. This gives you the distance from the nut to the 12th fret. There are no graduations denoting measurement on this tool. You are simply getting a distance between two points, whatever that distance may be. Note: In the shots below I have left the strings on the guitar. You would most likely be using this tool with the guitar un-strung.
The tool is locked into this position by tightening the screw on the small sliding block. The tool is then turned around 180 degrees. The small block is again placed on the 12th fret and the indicators on the large block give you the compensated distance from the 12th fret to the center of the saddle.
On the original Saddlematic these indicators are little points that you adjust in and out by hand. There are set screws to lock them in place. The instructions tell you that a good choice for most scale lengths is 2/32" on the treble side and 5/32" on the bass side. Getting these little points adjusted correctly is an excersize in futility. I found it difficult to get the points adjusted exactly.
My version uses two 8-32 screws instead of the points. Since there are 32 threads per inch on these screws it is very easy to adjust them. One full turn=1/32 of an inch.
The very edges of the screws are flat and quite thin. These should rest on the centerline of the saddle. Here's another area where I disagree with the instructions included with the original Saddlematic. They tell you that their points should lie at the very leading edge of the saddle. By measuring to the centerline of the saddle you have more room to fine-tune the compensation if needed.
Here's a comparison shot of the business end of the two jigs:
The business end of my homemade jig:
You can make this out of any hardwood or, as I did, aluminum. 1/2" square aluminum stock is available at any decent hobby shop. I think hardwood would be a lot more accessible to most people and would be easier to machine using standard woodworking tools and techniques. The rod is 3/16" music wire (very consistent in diameter across it's length). I picked it up at my local treasure-trove called True Value Hardware.
It's nice to have a good, clean, neat shop to work in:
And, of course, it helps to be comfortable while you're working:
If you have any questions about this jig, please email me.