The Truss Rod: A Curved Rod That Straightens a Guitar Neck

McHugh's main objects are "to provide an improved neck for stringed instruments, which is so constructed that it is not likely to spring or warp under the strains to which it is subjected in use, and one which should it become warped, may be straightened", and one "which may be adjusted or sprung to adjust or regulate the distance of the strings from the keyboard." The neck has a channel 4 in its upper side whose bottom 5 "is upwardly curved". "I arrange a truss rod 6 in the channel, the truss rod being curved to correspond to the bottom of the channel." Recesses 7 and 8 at the ends receive washers and nuts 9 and 10 threaded on the rod "so that it may be tensioned and adjusted"; a filler strip 11 covers it and a removable plate 13 gives access to nut 10. "The pull of the strings tends to swing the outer end of the neck upward thereby swinging the fingerboard away from the strings"; the truss bows the neck the other way. He adds that it lets wood be used "which has not been heretofore considered satisfactory for the manufacture of necks".

Capo the guitar at the first fret and hold the low E string down at the last fret where the neck meets the body. Measure the gap between the string and the top of the 7th or 8th fret with feeler gauges: that is the neck's relief. Slacken all strings and measure again: the relief shrinks as the strings' moment is removed. On a guitar with an adjustable rod, turn the nut an eighth of a turn at most and re-measure after the neck settles — never force it.

**Thaddeus J. McHugh** of Kalamazoo, Michigan, assignor to the **Gibson Mandolin-Guitar Company**, filed US 1,446,758 on 5 April 1921; it was granted on 27 February 1923. **Honest limits.** The string tension, neck section and offsets in the notebook are examples; a real neck is tapered and made of more than one material.