Saddle Radius Planner

What this tool is for

Calculate relative saddle-center targets from radius, string spread, action, and gauge. Geometry tools apply explicit models to named measurements. A coordinate or angle must still be checked against a physical drawing, real hardware, tolerances, and material behavior.

Use it when you can describe the current state and need a defensible next check. It is not a shortcut around inspection: preserve the starting state, change one variable, and verify the result under the same conditions.

Before you begin

Record fretboard radius model, reference positions, bridge location, string count and spacing, desired per-string action, and real diameters. Use one named vertical datum.

• Use a stable, tuned instrument unless the page specifically investigates tuning.
• Name the physical reference, unit, and test condition beside every important number.
• Keep the original measurements so any reversible change can be returned to baseline.

Input guide

Fretboard radius

supplies a measured geometric quantity whose datum and resolution should be written down.

Radius model

supplies a measured geometric quantity whose datum and resolution should be written down.

Optional compound end radius

supplies a measured geometric quantity whose datum and resolution should be written down.

Compound reference length

supplies a measured geometric quantity whose datum and resolution should be written down.

Radius measurement position

supplies a measured geometric quantity whose datum and resolution should be written down.

Bridge position from reference

provides a measured or counted input; confirm the allowed range and repeat the reading before relying on it.

Number of strings

provides a measured or counted input; confirm the allowed range and repeat the reading before relying on it.

Adjacent string spacing

provides a measured or counted input; confirm the allowed range and repeat the reading before relying on it.

Desired action per string

supplies a measured geometric quantity whose datum and resolution should be written down.

String diameters

records the actual string dimensions or supported set rather than a visual estimate.

Input and display unit

sets the interpretation and display unit; do not mix units elsewhere in the same run.

Input labels describe evidence, not targets. A placeholder demonstrates format only; it is never a recommendation for a particular guitar.

How the result should be read

Read offsets relative to the stated datum and verify with strings tuned. Adjust one saddle reversibly, retune, and check action and radius together.

Read priorities from top to bottom, but stop as soon as new evidence contradicts an earlier assumption. Save or print the result ticket with the entered conditions so another person can reproduce the decision.

Method and logic

Circular arc offsets are calculated at each string center, then combined with entered action and gauge terms as relative saddle-center targets. Compound radius is interpolated only over the declared reference.

The page keeps calculation and diagnostic claims deliberately bounded. Display rounding improves readability, while the underlying logic uses entered values; descriptive branches report relative tendencies and the evidence needed to confirm them.

Worked example

On a six-string 12-inch model, outer string centers sit higher on the arc than the center. Different desired actions further change saddle tops, so copying a bare 12-inch gauge is only a starting comparison.

The example demonstrates reasoning, not a universal setup specification. Substitute real measurements and repeat the final test before accepting the next action.

Assumptions and limitations

Bridge mechanics, fret wear, string stiffness, neck relief, compensation, and manufacturer saddle geometry are not solved here. The output is not a machining drawing.

Instrument design, service history, measurement error, and player technique can outweigh a calculator or checklist. Where manufacturer instructions exist for the exact hardware, use those instructions and record the revision consulted.

Safety and stop conditions

Stop for abnormal resistance, cracking, heat, odor, electrical sensation, moving wood or joints, a measurement that cannot be repeated, or any step that would remove material without a confirmed cause. Secure strings and stored mechanical energy before hardware work. Refer structural, fret-cutting, mains-powered, or uncertain repairs to a qualified technician.

Related workflow

• Fretboard Radius Matcher — Recover a circular radius from measured chord width and center sagitta, with error sensitivity.
• String Action Converter — Convert string height between millimetres and common inch fractions.
• Geometry Measurement Definitions — Name every datum before entering a number.

Open the related page that answers the next unresolved question; do not run every tool as if every system needs adjustment.