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Fig. 3. Tracing the bridge’s contours onto the saddle blank.
Once you have the saddle sanded to the correct thickness, place it in the slot and trace along the top of the bridge with a mechanical pencil (Fig. 3). The resulting line will give you a template illustrating where to carve the open ends and also provide a baseline for the saddle height.
Fig. 4. Measuring fretboard radius.
The next step is to determine the fretboard’s radius. This is a critical measurement because the saddle must match this radius for the action to be correct across all six strings. You need a radius gauge to take this measurement (Fig. 4). Various types of radius gauges are available from luthier supply companies, and if you search online you’ll also find free plans for crafting your own.
Fig. 5. Transferring the fretboard radius to the saddle blank at the height required for the new action, which is calculated during the initial evaluation. In this case, the new saddle will measure 4/64" on the treble side and 5/64" on the bass side.
This Martin’s fretboard has a 14" radius. Knowing I wanted an action of 4/64" on the 1st string and 5/64" on the 6th, I added 2/64" to the height of the original saddle and then marked a 14" curve on the new blank (Fig. 5). Adding 2/64" to the original numbers gave me 1/64th" extra height to work with, a slight margin that would allow me to confidently shape and file the saddle down to my target specs.