A micrometer screw converts thimble rotation into axial movement. Use the screw lead and thimble divisions to calculate the nominal scale interval and travel; instrument accuracy is a separate specification.
Micrometer Lead and Graduation Calculator
Enter screw lead, equal thimble divisions and signed divisions moved. The worksheet converts scale motion into turns, angle and ideal axial displacement; it does not predict measurement accuracy.
Equation Used
- One thimble revolution directly produces one screw revolution.
- Screw lead is constant and thimble divisions are uniformly spaced.
- The screw rotates relative to a fixed nut, producing axial movement along its guide.
- Backlash, pitch error, zero offset, force, elastic deformation, temperature and reading error are excluded.
Screw lead divided by thimble divisions gives the nominal scale interval. Actual measurement accuracy also depends on the instrument and its calibration.
Screw lead and thimble graduations
A micrometer screw converts thimble rotation into axial spindle motion. With direct coupling, one revolution advances the spindle by the screw lead. Uniform marks around the thimble subdivide that revolution, so one division corresponds nominally to lead divided by the number of divisions.
This kinematic increment is a scale interval. It does not establish how accurately a real instrument realizes or indicates that motion.
A scale-motion worksheet
Use the calculator to convert divisions into turns, angle and ideal axial motion. Real measurement requires the exact instrument's range, graduation, permissible error, measuring force, zero setting and calibration procedure.
Lead and scale conversion
Positive and negative m reverse the rotation and axial-motion signs under the stated convention.
Graduation example
For a 0.50 mm/rev lead and 50 equal divisions, the nominal scale interval is 10 micrometres per division. Moving +1 division is +0.020 turn, +7.2 degrees and +10 micrometres of ideal axial motion.
Scale interval is not instrument accuracy
Manufacturer documentation lists graduation and maximum permissible error separately and recommends periodic accuracy checks. A fine scale interval does not by itself establish backlash, repeatability or measurement uncertainty.
Micrometer scale questions
Is 10 micrometres per division the accuracy?
No. It is the nominal scale interval only.
What does a negative division count mean?
Rotation and axial travel are reversed relative to the positive sign convention.
Does the worksheet include sleeve turns or a vernier?
No. It models one direct thimble subdivision relationship only.
Manufacturer and metrology references
- Mitutoyo micrometer user manual: separate graduation, reading method, maximum permissible error and maintenance guidance.
- Mitutoyo Micrometer Heads: product-specific 0.5 mm spindle pitch and 0.01/0.001 mm graduations.
- Mitutoyo Micrometer Heads catalog: graduation, spindle pitch and accuracy listed as distinct specifications.
- NIST SP 250, Calibration Services Users Guide: micrometer calibration by comparison with gage blocks and special screw tests.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
