Good News for Guitarists — Automated Sander Finishes Frets Fast

A novel motion-control scheme on a custom woodworking sander has automated the precision finishing of fret boards for highquality guitars. C F Martin & Co. Dual sanding belts and a swinging workholder on the machine are controlled by a combination of linear and rotary servomotor axes. Formally, fret boards at guitar maker were made by hand, relying on the know-how of highly skilled technicians. They operated a special swinging jig that held the fret board and presented it to a motorized sanding belt. But particles tended to clog the belts and cause vibration, often forcing fret boards to undergo a second sanding for the right finish. A better method came from machine-builder , Bangor, Pa., which helped devise a more-controlled sanding process which removed material in small increments by means of rough and smooth sanding belts. The company worked with , Fort Smith, Ark., on a motion-control architecture that employs six axes of motion to automate the sanding process. Two Baldor vector motors power the rough and smooth sanding belts. Two servomotor axes with ball-screw jacks raise the belts once the workpiece has moved across the sanding faces. The swing-arm jig that holds the fret board is powered by two axes of motion: a servomotor to swing the fret board in an arc, plus a linear-motion axis that moves the swinging arm across the sanding belts. A linear motor with cog-free action handles the linear motion, the most critical of the axes. The motor sits in a stiff aluminum mounting frame and employs a special layout of the magnetic elements that eliminates any ripples of movement that can otherwise arise as the motor transitions between magnetic poles. The sanding scheme exploits the width of the sanding belts to aid uniformity and minimize the clogging effects of sawdust particles. Different woods also