Replacing a Mandolin bridge

Q: I have a harmony mandolin made around early 60s. the bridge collapsed and broke. i bought a replacement bridge, being way to high for the action I cut it down so the action is close to what is was before. my problem now is I cant get it tuned again. i have an electric tuner, every thing is flat. nothing is even close. any ideas what i should do, what I'm doing wrong.

Any help would be a help.
Thank you, Roy

A: Play the first harmonic by touching a string at its exact center and plucking it. Then play that same string at the twelfth fret. If the harmonic is sharp to the fretted note, move the bridge toward the fingerboard. If the harmonic is flat to the fretted note, move the bridge toward the tailpiece. The proper string length is different for each course, or pair of strings. The top of most mandolin bridges is staggered so that all the strings can be properly compensated, and play perfectly in tune, and the bridge be pleasingly straight. Some of the old Harmonys and some of the cheapest new replacement bridges are not compensated. With these you split the difference. Some courses will be slightly flat and some slightly sharp.

It is of the utmost importance that the bottom of the bridge fit the top exactly. Take the strings off. Put sticky backed 180 grit sandpaper on the mandolin where the bridge goes. Place the bridge and mark the placement on the sandpaper with black magic marker. The approximate placement will be double the measurement from the nut to the twelfth fret plus 1/16". The sliding method, above, will give you the exact placement. Scrub the bridge back and forth until there are no gaps between the feet and the top. It is very easy to "rock" as you sand. This rounds the bottom of the feet. Stewart-MacDonald sells a wheeled stabilizing mechanism that solves this problem and saves a lot of time. You can also use a scraper to cut off the roundness. There are more pounds per square inch on the heel of a woman's high heeled shoe than on the foundation of the Empire State Building. If the bridge bottom fits the top perfectly the weight of the strings is properly distributed. The mandolin sounds it's best and everyone is happy. An unfitted bridge focuses all the weight on the spots where the bridge does touch the top. The top can be dented, deformed or cracked. A slick trick with an adjustable bridge is to replace only the broken top and reuse the old bottom that fits.

On a 60s Harmony you are probably also due for fret filing, or even a plane and refret or a neck reset. The warp of the neck and the action set can also effect your intonation. Remember to use fresh strings for sliding the bridge. Old strings vibrate unevenly and will give you a false bridge placement.

Steve Mason