Scale length, adjustable bridges, and saddle placement

[Hardrock]

Hi again. I'm building my first guitar (lap slide).

I've decided on a 25-1/2 inch scale and an adjustable bridge. How should the scale be measured, from the inner side of the nut:

- to the mid-range of the travel of the individual string saddles?
- to some other point within the range of travel of the individual saddles?
- to the front of the adjustable bridge (per some plans)?
- other?

Thanks a heap, again, for helping a newbie
-jbb

[charles Tauber]

The "scale length" generally refers to the theoretical vibrating string length and is used to calculate the fret positions. Usually, it does not include compensation.

Many makers compensate the nut position by moving the nut 1/2 a fret slot closer to the first fret - they cut the end of the fingerboard centered on the "zero" position.

The amount of compensation at the saddle varies with a variety of factors including string diameter and string height (if depressing the strings to fret them). It is common to add about 2 to 3 mm for the high E string and 4 to 5 mm for the low E string. It makes sense to centre the adjustment of individual adjustable saddles on those measurements. In doing so, note that the B string will generally require about 2 mm more compensation than its neighbouring strings - unless the G string is unwound. Your bridge placement should accommodate that.

[Talldad]

The 25 1/2” measurement goes from this side of the nut to a line, parallel to the nut on the soundboard. That is your scale length.

Typically a top e string needs around 2mm extra length and a bottom E needs 6mm extra length. This is called compensation and is why saddles are built diagonally.