Intonation correction is the process of positioning the contact point for each string on the bridge's saddle so that the string notes (intonates) properly at each of the frets up and down the neck. Different gauges of strings require slightly different string lengths because thicker strings tend to change pitch more quickly than thinner strings when they are pressed and stretched to the fretboard. (The string is being "choked" as it is pressed down and that causes its pitch to increase.) So, as the gauge increases, the "string scale" (not the "fret scale") needs to be increased slightly. This is why you see the small saw-tooth stepping on the top of the bridge saddle for each set of strings.

The bridge saddles on most solid-body guitars feature adjustable contact points for each string so that the optimum intonation can be fine tuned. But mandolins and banjos feature fixed intonation points and are basically an average contact point for several gauges of strings. In fact, they are actually the average contact points for the same gauge of strings.

If that last sentence confuses you, you may or may not be aware that a particular wound string gauge in one brand may be comprised of different components than the same gauge in another brand. Wound strings are comprised of a core wire with an outer wire wrapped around it. And, there are several ways to make a wound string. As this diagram shows, a .034˝ string (for example) can be made with a .014˝ core wire and .010˝ wrap wire or a .016" core wire with a .009˝ wrap wire or a .018˝ core wire with a .008˝ wrap wire. And, of course, there are many more combinations for this and other gauges of strings.

If you have a bridge that intonates perfectly for a brand of one set of mandolin strings and you change to another brand that has different core/wrap wire combinations on its wound strings, the bridge may intonate differently.

One question that often arises is "If the intonation position moves back as gauges get larger, then why is the intonation point for the third pair of strings (D) - which has a larger gauge than the second pair of strings (A) - closer to the nut?" Good question! While the third pair of strings (D) is a larger overall gauge, the third and fourth strings are wound strings in which the core or center wire is actually a smaller gauge than the plain (A) strings, so the intonation point must be closer to the nut.

We have two scale lengths at play here: the string scale and the fretting scale. The string scale is predicated on a particular gauge of string's intonated length; the fretting scale is predicated on the fret locations. For example, the F5 mandolin has a 13-15/16" string scale but a 13-7/8" fretting scale. With guitars and mandolins, the string scale is usually based on the second string's length, and the fretting scale is based on the first string's length.

Why don't fiddles have an intonated bridge? Another good question. First of all, the violin (fiddle) bridge wins the medal for the ultimate bridge design. In the violin bridge, there is no direct route of the strings' energy to the soundboard. The energy of each string is attenuated by an opening between the string's contact point at the top of the bridge and the bridge feet. But aside from bridge design, the intonation of the strings on a violin is controlled by the location of the musician's fingers. In the absence of frets, the musician locates and perfects the strings intonation as each note is played.

Some banjo bridges are made with intonation correction notches. For those banjo players who choose straight, non-intonated bridges, they usually turn the bridge slightly counterclockwise to create a pseudo-intonation correction.

Around 1918, Gibson engineers began working on bridge saddles with adjustable contact points. These were made in the form of inserts that fit into a groove on the top of the bridge and could be interchanged or turned around to achieve the ideal intonation. Aside from the fact that the parts were fragile and occasionally got misplaced, the movable insert system presented the musician with too many options, and frustration in using it caused the design to be very short lived in Gibson's accessory line.

We've done some interesting things with our bridge saddles and have tested many different ways of making them. One major change we made is that the intonation notches, as a group, are positioned on the centerline of the saddle to keep the saddle from cocking at an angle on the bridge's posts.

The most critical job of inlaying the rosettes into an F or A model mandolin with an oval soundhole is cutting the channel. This is a delicate and tedious process. The second most critical part of the job is getting the rosette clamped securely to the soundboard when gluing in place. One of the key problems that arise in the gluing process is getting a sufficient number of clamps onto the rosette to press it securely into the channel. Unfortunately, there is just not a lot of room to get regular C-clamps into the soundhole opening so some other clamping method is called for.

For gluing rosettes, we've made a series of small C-clamps from U-shaped aluminum channel. We cut ½" wide pieces from ¾" channel stock and then drilled and cut an 8-32 thread into one lip into which we threaded some small thumb screws.

We can get six or seven of these clamps to fit easily around the soundhole, and we use a small wood caul between the clamp and the rosette. To ensure that the cauls do not accidentally get glued in place we use thin strips of wax paper between the cauls and the rosette. The clamps are small, effective, easy to make, and inexpensive.

By the way, we've just finished a new instruction sheet for inlaying rosettes. Since it won't be posted to our web site for several weeks, I'd be glad to send you a free PDF file of it if you email me (siminoff@siminoff.net) and put ROSETTE INSTRUCTIONS in the subject line.