Inconsistent inter-letter spacing could improve immensely if the same slope for lettering , was maintained for ligatures. Although italic letters may be well formed, the spacing may be irregular. If the same slope line is followed with your ligatures, the letter spacing will largely take care of itself.
In the first example, I’m using ‘under-linking’ where the ligatures join to the next letter about half way up. In the second version I’m using ‘over-linking’ where the ligatures join to the next letter over a top curve, anticipating the upper curve of the letter ‘n’ which follows.
With the two styles of joining, neither is better than the other - they are both equally valid. Although the letters are basically the same size and shape, the first version is shorter because the under-linking creates narrower spaces than the second over-linked version.
It’s quite possible to use this grid to help with letter spacing even if you don’t use ligatures, by lifting the pen at the bottom of each letter and ‘feeling’ the space as your nib travels up the slope line, without touching the paper. The under-linked first version, is particularly effective for this.
