Installing a new saddle is not “drop in” situation. Sometimes just a thin ebony shim under the saddle is satisfactory. Each saddle is custom fit to the existing saddle slot in each individual instruments bridge and should fit so as to be snug, definitely not loose. The bridge saddle slots vary in width by as much a .005″ (.13mm) but the saddle should fit to within 001″ (.02mm). Not over tight or wedged in but tight enough to almost need pliers to aid removal. This is very important so as to transmit the string vibrations directly to the bridge and top without tonal loss. The saddle and bridge area is definitely one of the most important for tone!
The saddle also needs to be adjusted for each instrument as to the correct treble and the correct bass height. So just sanding evenly off from the bottom is hit or miss in achieving the correct action height. We like (after the correct relief) .070″ (1.82mm) treble and .094″ (2.41mm) bass to the top of the 12th fret.
I recommend leaving the action on the slightly high side and going slowly when lowering otherwise tone can be diminished even before buzzing occurs.
When installing the strings and tuning up for the first time with a new saddle, tighten the strings about half way and adjust the strings for even spacing over the saddle top and inline with the relief slots behind the saddle. Otherwise the strings will set into the saddle with an uneven spacing and will be always forced to set unevenly because the strings notch the top of the saddle the first time they are tightened.
Usually the reason someone wants a new saddle is that the action was lowered too far causing unpleasant buzzing to occur! Sometimes releasing tension on the truss rod of a neck (one that is too straight or flat) will be all that is needed to correct buzzing. A neck with the proper relief will allow the bass strings to oscillate without damping and buzzing and also makes the higher notes easier to fret. This is because the higher the note and the shorter the string, less relief (slightly) from the fretboard is necessary. Find out more about action height on our Guitar Care page.
The other reason a saddle is needed is because the instrument has been dangerously dried out too much in low humidity causing the top to drop down and perhaps go concave and lowers the stings toward the frets. If there are sharp edges on the frets and buzzing of the strings on the frets which didn’t happen previously the instrument has been over dried! An over dried instrument can crack and must be re-humidified to at least 40% relative humidity. Find out more about humidity on our Guitar Care page.