Relly low action

[Roger Häggström]

Working on the Levin acoustic with a floating bridge. The customer plays with a hard plectrum and wants the lowest action possible. Mensur 63 cm, 10" radius and a set of 0.11 strings.

As it is now the action at 12th is 1.4 mm (0.056 inch) for treble e and 2.4 mm (0.095 inch) bass E. The guy wants lower. I have a very small relief in the middle of the fretboard and a nice curve on the top of the frets, about 0.05 mm (0.002 inch) in the middle of the fretboard. The relief is made for the whole length of the fretboard. No slope off.

The action at the 1th fret is a tad higher than from a zero fret. The fretboard plays fine until around the 9th fret.

I can increase the relief sanding on top of the frets (no trussrod) or I can make a "slope off" or flatten the frets from the 9th fret to the last making the problem frets lower.

Any thought about what relief to use for an insane low action? Is a "slope off" needed for this?

[Christopher Parker]

Almost zero relief is appropriate for very low action (somewhere between .05mm and .13mm). It's best if the nut or zero fret is exactly as high as the first fret. "Slope off" under string tension is not necessary. A consistent relief is okay, but relief that slightly flattens out higher up the neck (under string tension) is ideal. Obviously, imperfections in fret/fingerboard levelness will manifest as buzzing and dead notes more readily with low action. Therefore a precise fret job is imperative.

[Roger Häggström]

Thanks a lot. It seems that I got most of the parameters right then. I need to flatten out the relief beyond the 9th fret.

[steven gallagher]

You mentioned you had a custom sanding beam made with relief built in. I don't think that helps.

If you've got a friend with CNC equipment, why don't you have him make you some compound radius leveling beams? That would help with reducing the amount of relief you need and getting lower action.

[Roger Häggström]

The beam I use helped me get a really small and even relief along the fretboard. The customer don't bend strings but wants to have clean fretted notes all the way using a hard pick. As I understand it compound radius is great for bending strings without fretting out.

[steven gallagher]

A compound radius, which really means a conical section, is the only way to get all the strings parallel to the fretboard, unless you have a flat fingerboard or the strings are all parallel to each other.

The difference between a fixed and compound radius is small, but is greater the smaller the radius of the fret tops is. A 10" radius is on the small side, IMO.